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TL;DR: A cold-climate heat pump will heat a custom home in eastern Idaho and Teton Valley through a normal winter, and on most of our builds it is now the primary system. But I still put a furnace or a boiler behind it on anything above about 6,000 feet, because our design temperature runs near -10°F and a single point of failure at -10°F is not a design, it is a gamble. The honest answer for 2026 is usually both: a cold-climate heat pump doing 80 to 90 percent of the hours, with gas or propane backup for the rest.

Heat pump or furnace: which one belongs in an Idaho custom home?

If you are building new in eastern Idaho or Teton Valley, a cold-climate heat pump should be your starting assumption, and a furnace should be the thing you add on purpose rather than the thing you default to. That is a real change from how I was speccing houses even five years ago, and it is not because of a rebate or a trend. It is because the equipment finally got good enough at low temperatures to be the primary heat in a well-built house at 6,000 feet.

Here is the part most articles skip. A heat pump is not a different kind of furnace. It is an air conditioner that can run backwards. In summer it moves heat out of your house. In winter it moves heat from the outdoor air into your house, which sounds impossible when it is 5°F outside, but cold air still holds heat energy. The machine just has to work harder to find it. That is the entire argument in one sentence: a heat pump moves heat, a furnace makes heat. Moving is cheaper than making, right up until it gets cold enough that moving gets hard.

So the question is never really “which one is better.” It is “at what outdoor temperature does the cheap option stop being the cheap option, and what happens the night it does.” Everything below is me answering that for the specific valleys we build in.

Will a heat pump even work when it is below zero here?

Yes, if you buy the right one, and no, if you buy a standard one. That distinction is the single most expensive thing a homeowner can get wrong on this decision, and almost nobody explains it.

A standard air-source heat pump has no low-temperature performance requirement at all. None. It can meet its efficiency rating entirely on mild-weather performance and fall off a cliff at 20°F, and it still gets to be called a heat pump. A cold-climate unit is a different product held to a different bar.

To carry the ENERGY STAR Cold Climate designation, an air-source heat pump has to deliver a coefficient of performance of at least 1.75 at 5°F, hold at least 70 percent of its 47-degree heating capacity down at 5°F, and hit HSPF2 of 8.1 ducted or 8.5 non-ducted along with SEER2 of 15.2. Those thresholds are published in the ENERGY STAR key product criteria for air-source heat pumps, and that capacity-retention number is the one that matters most here.

Translate it: a cold-climate unit at 5°F still has roughly three quarters of the output it had at 47°F, and it is still producing about 1.75 units of heat for every unit of electricity it draws. A standard unit at the same temperature might be at 40 percent of capacity and barely better than a resistance coil. Same category, same marketing word, completely different machine.

Now the local number. The 99 percent winter design temperature we calculate to in Teton Valley runs right around -10°F, and on the Idaho Falls and Rigby side it is milder, closer to -5°F. Design temperature means the house has to hold temperature in weather that cold, not that it never gets colder. It does get colder. We have all watched the thermometer go past -20°F in Driggs.

At those temperatures even a cold-climate heat pump is losing capacity and its efficiency is approaching break-even against straight electric heat. That is not a failure of the technology. It is physics, and it is exactly why I do not leave a house with only one heat source. For more on what our winters actually do, I wrote up the eastern Idaho climate year-round in detail.

What does a heat pump cost compared to a furnace?

I am going to be careful here, because there are two different kinds of numbers and mixing them is how people end up angry.

SwagerBuilds does not publish an equipment rate card. Our custom home pricing starts at $400 per square foot and goes up on the Idaho and Teton Valley side, and starts at $1,000 per square foot and goes up on the Jackson Hole side, and mechanical is inside that, specified to the house we actually design with you. What I can give you is third-party market data so you can see the relative shape of the decision. The ranges below are 2026 national market figures from HomeGuide, not SwagerBuilds pricing and not a quote:

System (2026 market data, installed)	Typical range	Notes
Ducted air-source heat pump	$10,000 – $25,000	$20,000 – $32,000 on homes over 3,500 SF
Ductless mini-splits	$2,000 – $17,000	Scales with the number of indoor zones
Gas furnace, 80-89% AFUE	$3,800 – $6,200	Needs a flue; not what I would install new
Gas furnace, 90-95% AFUE	$5,200 – $8,800	Condensing, PVC venting
Gas furnace, 96%+ AFUE	$7,500 – $12,000	Where new construction should start

Read that table correctly. The furnace line looks cheaper because it is only half a system. A furnace heats and does nothing in July. A ducted heat pump is your heating and your air conditioning in one box, and air conditioning is no longer optional in this valley the way it was when I started. Smoke season alone has made a sealed, filtered, conditioned house a comfort item people will not give up. If you are comparing a furnace price to a heat pump price, the fair comparison is furnace plus air conditioner against heat pump alone, and the gap closes most of the way.

The second half of cost is the part nobody quotes: what it costs to run. That depends almost entirely on what fuel you can actually get at your lot, which brings us to the thing that decides this more than any brand or SEER rating.

Why propane changes the whole math in Teton Valley

There is no natural gas service in Driggs, Victor, or Tetonia. None. If you are building in Teton Valley, combustion heat means a propane tank on your property, delivered by truck, at a price that moves with the market and with how far up a snowy road your house sits. Idaho Falls, Ammon, Rigby, and Rexburg do have natural gas, and that single utility fact flips the recommendation.

Natural gas in Idaho Falls is cheap, stable, and piped. A high-efficiency furnace burning natural gas is genuinely hard to beat on operating cost at deep-winter temperatures, and I will spec one without hesitation on a Bonneville or Jefferson County build. Propane is a different animal. It carries a tank, a delivery schedule, a seasonal price swing, and a real failure mode where the truck cannot get up your driveway in February. When the alternative fuel is propane, the heat pump’s running-cost advantage gets much wider, and the case for making it the primary system gets much stronger.

Where you are building	What I usually lead with	Why
Idaho Falls, Ammon, Rigby, Rexburg	Cold-climate heat pump with a 96%+ natural gas furnace as dual-fuel backup	Natural gas is piped and cheap, so backup costs almost nothing to own and run
Driggs, Victor, Tetonia, Alta	Cold-climate heat pump as primary, propane furnace or boiler sized as true backup	No gas service; propane is the expensive fuel, so you want to burn as little as possible
Jackson Hole side	Heat pump plus hydronic or propane backup, engineered per lot	Colder design temps, bigger houses, stricter review; the load calc drives it
Off-grid or weak-service lots	Combustion primary, heat pump only after the electrical service is confirmed	A heat pump is an electrical load; if the service cannot carry it, nothing else matters

That last row is not theoretical. Electrical service capacity has killed more heat pump plans on rural Idaho lots than cold weather ever has, and it is one of the things we check during site evaluation rather than discovering at rough-in. If you are starting from raw ground, that whole category of problem is covered in how to prepare land to build a house in Idaho.

What is a dual-fuel system, and is it the safe middle?

Dual-fuel means one system with two heat sources and a thermostat smart enough to pick between them. The heat pump runs whenever it is the cheaper option. Below a crossover temperature you set, the furnace takes over. One set of ductwork, one thermostat, two ways to make the house warm.

On most of our builds this is the answer, and I will say plainly why: it removes the argument. You get heat pump economics for the vast majority of winter hours, because the vast majority of winter hours in eastern Idaho are above 20°F, not below zero. And you get a combustion appliance standing by for the week in January that makes the news. You are not betting your house on a single machine at -15°F, and you are not paying propane prices in October.

Where I set the crossover matters. Set it too high and you burn expensive fuel on mild days for no reason. Set it too low and you run the heat pump into its inefficient range and your electric bill spikes. On a natural gas house the crossover usually lands lower, because gas is cheap enough to hand off earlier without much penalty. On a propane house it lands higher, because every gallon you avoid burning is real money. That is a tuning decision, not a product decision, and it is one of the things I stay on top of through the first winter after you move in.

Do mini-splits make sense in a custom home?

In the right places, yes. As a whole-house strategy on a $2 million custom home, usually no, and I will tell you that even when a client has read that mini-splits are the efficient choice.

Ductless mini-splits are excellent at conditioning a specific space independently. Where they earn their keep on our builds is a bonus room over a garage that the main system fights, a detached office, a shop space, a guest suite that needs its own setpoint, or a great room with a wall of glass and a load nothing else wants to carry. Those are real problems and a mini-split solves them cleanly.

What I do not like is a custom home with eight wall cassettes hanging in eight rooms. You get indoor heads on your walls in a house where you paid for the millwork and the window detailing, you get eight filters nobody remembers to clean, you get refrigerant lines run all over the building, and you get no central filtration, which matters more every smoke season. A ducted system with a properly designed distribution layout gives you hidden equipment, one filter rack that can take a real MERV filter, and balanced air in every room. On a custom home, that is worth more than the handful of efficiency points.

The honest exception: a small, very tight, open-plan house can be heated well by two or three mini-splits and it is a legitimately good solution. It is just not what most people building a $1 million-plus custom home are describing to me.

I want radiant floors. Does that settle it?

No, and this is the most common mix-up I untangle in design meetings. Radiant floor heat and a heat pump are not competing choices. Radiant is a delivery method. A heat pump is a heat source. You can absolutely have radiant floors fed by an air-to-water heat pump instead of a boiler.

What radiant does not do is cool, dehumidify, filter, or ventilate. So if you want radiant floors, you still need an air system for summer and for air quality, and now you are buying and maintaining two distribution systems in one house. That is a legitimate choice. It is comfortable, it is quiet, and in a high-ceilinged mountain great room it feels different in a way people who have lived with it will not give up. It is also meaningfully more money, both up front and in maintenance, and it does not replace the decision in this article. I broke the economics down separately in what radiant floor heat costs in Idaho.

The pattern I see work best: radiant in the spaces where you will feel it every day, meaning primary bath, mudroom, and the main living floor, with a ducted heat pump handling the rest of the house, the cooling, and the filtration. Not radiant everywhere out of principle.

Why the house decides this before the equipment does

Here is the thing I wish every homeowner understood before shopping for equipment: a heat pump works better in a better house, and “better house” is not a vague compliment. It is insulation, air sealing, and glazing, and it is decided in design, months before anybody orders a condenser.

Idaho enforces the 2018 IECC with state amendments, effective January 1, 2021, which you can confirm through the Department of Energy’s state code status page for Idaho. In our climate zone that means roughly R-49 at the ceiling, R-22 in the walls or R-13 plus R-5 continuous, R-19 or R-15 continuous at basement and crawl walls, a U-0.30 window maximum, and an air-leakage target of 5 air changes per hour at 50 pascals. That is the legal minimum. It is not a target I am proud of hitting.

Why it matters for this decision: a tighter, better-insulated house has a smaller heating load, and a smaller load means the heat pump’s reduced capacity at 0°F is still enough to cover it. Build loose and you force the system into its weak range on exactly the nights you need it, then blame the heat pump. Build tight and the same equipment coasts. The envelope decision and the mechanical decision are the same decision made twice, and if you only have budget to upgrade one of them, upgrade the envelope. It lasts fifty years; the equipment lasts fifteen.

That is why these posts connect: spray foam versus blown-in insulation, whether triple pane windows are worth it in Idaho, basement versus crawl space versus slab, and the broader list of energy efficient custom home features worth paying for. Every one of them changes the size of the machine you need.

What is Manual J, and why will I not spec a system without one?

Manual J is the room-by-room heating and cooling load calculation for a house. It takes your actual plan, your actual window schedule and orientation, your actual insulation assemblies, your actual air-tightness target, and your actual design temperature, and it produces the number of BTUs each room loses on the coldest night. The ACCA Manual J standard is the ANSI-recognized method for this and national codes require it.

What happens without it is that somebody sizes your system off square footage and a rule of thumb, rounds up to be safe, and you get equipment that is too big. Oversizing is not harmless. An oversized system short-cycles, which means it blasts, satisfies the thermostat fast, and shuts off before it has evened out the house or pulled moisture out of the air. You get hot and cold rooms, more wear on the equipment, and worse comfort than a correctly sized smaller system would have given you. On a heat pump it is worse, because these systems are at their most efficient running long and steady at part load, which is exactly what oversizing prevents.

So on a SwagerBuilds build, the load calc comes before the equipment selection, and the duct design comes from the load calc, not from wherever the joists happened to leave room. That coordination with the mechanical engineer is part of what we handle in-house during design. You are not expected to go hire an engineer and bring us a spec. That is covered under our custom home design services and the design and engineering side of the business, and it is the main reason we lock scope before we lock a construction price. I wrote about why that order matters in the design phase and getting a real number before signing.

Where does fresh air and ventilation fit in?

If you build the house tight, and you should, you have to bring fresh air in deliberately. A tight house with no ventilation plan holds moisture, cooking odors, and whatever the air inside is doing. The equipment for this is an HRV or an ERV, a heat or energy recovery ventilator, which exhausts stale air and brings in fresh air while recovering most of the heat from the air it is throwing away.

HRV or ERV is a question I get asked as though it is a big fork in the road. In practice the real-world difference is slight. The usual summary from the building-science world, including GreenBuildingAdvisor’s take on HRV versus ERV, is that houses are happiest around 20 to 40 percent relative humidity while people are comfortable from 30 to 70 percent, and either machine, sized and commissioned correctly, will get you there in our dry climate. The thing that actually determines whether it works is whether it was sized right, ducted to the right rooms, balanced, and commissioned. An ERV installed badly is worse than an HRV installed well, every time.

Budget for it as part of the mechanical system, not as an upgrade. In a house hitting modern air-tightness numbers, it is not optional equipment.

Are there still tax credits for this in 2026?

No, and you need to hear that from somebody before you build a budget on a number you read in an old article. As of today, the federal residential clean energy and efficiency credits that used to apply here are gone. The 25C energy efficient home improvement credit is not allowed for property placed in service after December 31, 2025, and the 45L new energy efficient home credit is not allowed for a qualified home acquired after June 30, 2026. The IRS lays this out in its FAQ on energy efficient home improvement and residential clean energy credits.

Practically, that means a 2026 heat pump decision has to stand on its own operating-cost math, with no federal credit propping it up. The good news is that it still does, especially on the propane side of the pass. The bad news is that any quote or comparison you were handed before 2026 was built on assumptions that no longer exist. Same goes for utility and manufacturer incentives, which change on their own schedules. Verify anything you are counting on in writing, in the month you are buying.

What is not included when someone quotes you a number?

Every time a dollar figure shows up in a conversation about mechanical systems, the next honest question is what is missing from it. Usually a lot:

• Ductwork and distribution. Equipment pricing frequently assumes existing ducts. On new construction, the duct design and install is a real line item and it is where comfort is won or lost.
• Electrical service and circuits. A heat pump is an electrical load. Panel capacity, a dedicated circuit, and sometimes a service upgrade ride along with it.
• The backup appliance. If you are going dual-fuel, that is two pieces of equipment, not one.
• Propane tank, pad, line, and permitting where there is no gas service.
• The ventilator. The HRV or ERV, its ducting, and its commissioning.
• Load calculation and engineering. Manual J, duct design, and the engineer’s coordination.
• Commissioning and balancing. The step most commonly skipped, and the one that decides whether the system you paid for performs like the system you paid for.
• Snow and site realities. Outdoor unit placement up off the ground, out of the drip line, and clear of where the roof dumps. I have seen a condenser buried to the top by one slide off a metal roof.

This is the same pattern as every other part of a custom home, which is why I keep writing about it. If you want the full version of that conversation, read the hidden costs of building a custom home in Idaho and why three custom home bids do not compare. Mechanical is the single most common place where two bids look $30,000 apart and are actually quoting different houses. How allowances are written matters too, which I covered in construction allowances on a custom home.

How this actually gets decided on a SwagerBuilds build

I have been in construction 20 years and I am involved in every phase of every build we take, so this decision does not get handed off to whoever shows up to set equipment. The sequence looks like this.

During design, we lock the envelope first: assemblies, glazing, air-tightness target. Then the mechanical engineer runs the Manual J against that actual house, not a square-footage guess. Then we look at your lot: what fuel can get there, what the electrical service can carry, where an outdoor unit can live and survive a Teton Valley winter, and whether snow shed or a long driveway changes anything.

Then, and only then, we pick equipment and design the distribution. Then it gets installed, commissioned, and balanced, and I check the numbers myself rather than taking a startup sheet’s word for it. Then we are back through the first winter under the same workmanship warranty that covers the rest of the build, tuning the crossover point against real weather and your real bills.

Nine times out of ten in eastern Idaho that lands on a cold-climate ducted heat pump with a high-efficiency gas or propane furnace behind it, radiant in a few rooms where you will actually feel it, an ERV or HRV sized to the house, and a filter rack that can handle August. But I am not going to tell you that is your answer before I have seen your plan and your lot, because the whole point of a load calculation is that your house is not the average house.

If you are planning a custom home in Teton Valley, Jackson Hole, or eastern Idaho and want this settled properly instead of defaulted into at rough-in, start a conversation with us. Call the office at (208) 520-0636 or reach out through the site, and we will walk your lot and your plan before anybody talks about equipment.

Our pricing starts at $400 per square foot and goes up on the Idaho and Teton Valley side, and starts at $1,000 per square foot and goes up on the Jackson Hole side, with a fixed design fee quoted per project and a fixed construction price after design lock. You can see how that per-square-foot number behaves in practice in cost per square foot to build in Teton Valley and cost to build a house in Idaho per square foot.

FAQ

Can a heat pump heat a house in Idaho all winter by itself?

A cold-climate heat pump can carry a well-built Idaho house through nearly all of a normal winter on its own. I still install backup heat above about 6,000 feet, because our design temperature is near -10°F and real cold snaps go colder, where capacity and efficiency both drop. On a tight, well-insulated house in Idaho Falls or Rigby, a heat pump alone is more defensible than most people expect. In Driggs or Victor, plan on backup.

Is a heat pump cheaper to run than a propane furnace in Teton Valley?

In most hours of the heating season, yes, and that gap is wider in Teton Valley than almost anywhere else in the state because there is no natural gas service in Driggs, Victor, or Tetonia, so the alternative is trucked propane. The heat pump loses its advantage only in the coldest stretches, which is exactly what a dual-fuel setup with a tuned crossover temperature is built to handle.

What size heat pump do I need for a 3,000 square foot custom home?

There is no honest answer from square footage alone, and anyone who gives you one is guessing. Two 3,000 square foot houses in Driggs can differ by more than 40 percent in heating load depending on glazing area and orientation, insulation assemblies, and air-tightness. That is what a Manual J load calculation exists to answer, and it is run on your actual plan during design.

Do I need air conditioning in a custom home in eastern Idaho?

It is no longer something I would leave out of a new custom home. Summers run hotter than they used to and smoke season has made a sealed, filtered, cooled house something people are not willing to give up. The practical argument for a ducted heat pump is partly this: it is your air conditioning and your heating in one piece of equipment, so cooling stops being a separate purchase.

Are there any federal tax credits left for a heat pump in 2026?

No. The 25C energy efficient home improvement credit does not apply to property placed in service after December 31, 2025, and the 45L new energy efficient home credit does not apply to a qualified home acquired after June 30, 2026. Any article or quote assuming those credits is out of date. Check current utility or manufacturer incentives separately and get them in writing in the month you buy.

TL;DR: Spray foam is not automatically the right answer in Idaho, and blown-in is not automatically the cheap answer. Closed-cell spray foam buys you about R-6.5 per inch plus an air seal and a vapor retarder in one pass. Blown-in cellulose or dense-pack buys you more R-value per dollar in a deep cavity. On the custom homes I build in Teton Valley and eastern Idaho, I use both — foam where air sealing and moisture control matter, blown-in where depth is free.

I have been in construction for 20 years, and insulation is the single most common place I see a custom home get quietly cheapened. Nobody walks through a finished house and says “nice cavity fill.” It is buried behind drywall three weeks after it goes in, it never shows up in a listing photo, and it is the one system you cannot fix later without tearing the house apart. So it is a great place to save money if the goal is to win a bid, and a terrible place to save money if the goal is to live in the house.

This post is the honest version of the conversation I have with owners at the design table. No brand pitch, no “foam is always better.” Just what each material does, what Idaho code actually asks for, where I spend the money, and what I would skip.

What insulation does Idaho code actually require?

Idaho enforces the 2018 IECC with state amendments, effective January 1, 2021, per the U.S. Department of Energy’s code status page. Eastern Idaho and Teton Valley sit in climate zone 6. Here is what that means in numbers, and what I build to instead.

Assembly	Idaho code minimum (zone 6)	What I spec on a custom build	Why
Ceiling / attic	R-49	R-60 blown-in, vented attic	Blown depth is nearly free. The only cost is more material and a taller baffle.
Above-grade wall	R-22, or R-13 plus R-5 continuous exterior	R-21 cavity plus R-5 to R-10 continuous exterior	Continuous exterior insulation kills thermal bridging through the studs. Cavity R-value alone does not.
Rim joist / band	Treated as wall	Closed-cell spray foam, 2 to 3 inches	Worst air leak in the house and almost impossible to seal with batts.
Floor over unconditioned space	R-30	R-30 blown-in with a hard air barrier below, or foam	Batts sag, fall and stop touching the subfloor.
Basement wall	R-19, or R-15 continuous	R-15 continuous rigid or closed-cell spray foam on the concrete	Concrete is a moisture source. Fiberglass against it is a mold experiment.
Crawl space wall	R-19, or R-15 continuous	R-15 closed-cell spray foam, sealed crawl	See the basement vs crawl space vs slab breakdown.
Blower-door air leakage	5 ACH50, tested on a 20% sample of each builder’s homes	Every house tested, target under 3 ACH50	A sample requirement is not a quality program.

Two things in that table deserve a flag. First, Idaho’s amendment softened the national wall number. The unamended 2018 IECC asks for R-20 cavity plus R-5 continuous in zone 6; Idaho will take a straight R-22 cavity with no exterior layer. That is legal and it is also the weaker assembly, because every stud is a thermal short circuit straight through the wall.

Second, the blower-door requirement is a sample. Per the same Idaho summary, beginning July 1, 2021 a minimum of 20% of each builder’s homes must be tested. So four out of five houses in this state can be code-compliant on paper without anyone ever measuring whether they leak. If your builder cannot hand you a blower-door number for your specific address, you do not know what you bought.

Spray foam vs blown-in vs batts: what is the real difference?

Insulation does two separate jobs: it slows heat conduction (that is the R-value) and it stops air movement. Most people only shop the first one. Air leakage is what actually makes a house feel cold and drafty at 10 below, and it is where spray foam earns its price.

Material	R per inch	Air seals?	Vapor behavior	Market cost per SF of surface (2026)	Where it belongs
Closed-cell spray foam	~6.5	Yes, fully	Class II vapor retarder at ~1.5 to 2 inches	$3.00 – $5.00	Rim joists, crawl walls, basement walls, unvented roofs, tight spots
Open-cell spray foam	~3.5 – 3.8	Yes	Vapor open, needs a separate retarder in zone 6	$1.50 – $3.50	Interior sound walls, deep cavities with a vapor plan
Dense-pack cellulose	~3.5 – 3.8	Slows air, does not seal	Vapor open, buffers moisture	$1.00 – $2.80	Wall cavities behind a good air barrier
Blown fiberglass (attic)	~2.2 – 2.7	No	Vapor open	$1.00 – $2.80	Vented attic floors, where depth is cheap
Fiberglass batts	~3.1 – 3.4	No	Vapor open	$1.00 – $2.60	Budget cavity fill, installed perfectly or not at all
Mineral wool batts	~4.0 – 4.3	No	Vapor open, does not burn	$1.50 – $3.80	Walls near a fire-exposed exterior, sound separation

Read that table one more time with the air-seal column in mind. A fiberglass batt and a shot of spray foam can hit the same R-value on a label and perform nothing alike, because air moving through a batt carries heat with it and the label test does not have any wind in it. Closed-cell spray foam at R-6.5 per inch, confirmed in GreenBuildingAdvisor’s spray foam primer, is also the only one on that list that air seals, blocks vapor and adds R-value in a single pass.

That is also why it costs the most. You are buying three products.

Which insulation goes where in a mountain house?

The right answer is almost never one material for the whole house. It is foam where a leak or a wet surface would cost you, and cheap R-value everywhere depth is free. Here is how I split it.

Rim joists get closed-cell spray foam, every time. The rim is where the floor framing lands on the foundation — a long, skinny, interrupted band of exposed wood on every exterior wall. In an older house it is the biggest single hole in the thermal envelope. Two to three inches of spray foam seals it and insulates it at once. I have never regretted that money.

Crawl space and basement walls get closed-cell spray foam or rigid board. Concrete is wet. It stays wet for years after the pour, and it wicks ground moisture after that. Put fiberglass against it and you have built a cold, damp sandwich. Building Science Corporation has been publishing this for two decades; their digest on vapor barriers is the plain-English version. Foam against the concrete keeps the wall warm enough that it never hits dew point on the inside.

Above-grade walls get cavity insulation plus exterior continuous insulation. This is the one most Idaho houses skip. A 2×6 wall framed at 16 inches on center is roughly 23% wood by area once you count plates, headers and jack studs. Wood is about R-1.25 per inch. So a quarter of your “R-21 wall” is actually R-7. Adding a continuous layer outside the sheathing — rigid foam or mineral wool board — is the only way to fix that, and it also keeps the sheathing warmer, which is a moisture win. If you want the framing side of this, I wrote up how stack framing works and why it matters.

Attics get blown-in, deep. In a vented attic, the only cost of more insulation is more material. Going from R-49 to R-60 is a rounding error on a custom-home budget. Blown cellulose or blown fiberglass, installed to a marked depth, with baffles at the eaves so the soffit vents stay open and the insulation does not get wind-washed back off the top plate.

Interior walls get mineral wool or open-cell spray foam for sound. Not for energy. For not hearing the laundry room from the primary bedroom. It is one of the cheapest upgrades on the upgrades-worth-the-money list and it gets cut constantly.

Does spray foam save enough on heating to pay for itself?

Honest answer: on R-value alone, usually no. On air sealing, often yes, and the payback is not only in dollars.

Here is the math problem with foam-everything. Going from R-21 to R-30 in a wall cuts that wall’s conductive heat loss by about 30%. Going from R-49 to R-60 in an attic cuts that attic’s loss by about 18%. Those are real but diminishing. Doubling the R-value never halves the bill, because walls and ceilings are only part of the load — windows, air leakage, ventilation and ground contact are the rest. Our triple pane window post runs the same kind of math on glass.

Air leakage is different. It is not diminishing in the same way, because a leaky house at 10 below is not losing heat slowly through an assembly, it is pumping warm air out the top of the building and pulling cold air in at the bottom. Tightening a house from 5 ACH50 to 2 ACH50 changes how it feels, not just what it costs: no cold floors at the exterior walls, no drafts at outlets, no ice damming from warm air leaking into the attic, and far less dust and pollen coming in through the assembly instead of through a filter.

So the way I think about spray foam is not “what is the payback.” It is “where would an air leak cost me comfort, a moisture problem or a callback.” That is a short, specific list, and spray foam goes exactly there.

One more thing worth saying out loud: a tight house needs mechanical ventilation. If you air seal a house properly and do not install a balanced ventilation system — an HRV or ERV — you have built a bottle. That is not an argument against sealing. It is an argument for doing both, and it belongs in the mechanical design, not in a change order. I cover the rest of the envelope-and-mechanical picture in which energy efficient features are actually worth paying for.

What is the catch with spray foam in a cold climate?

There are four, and a good builder talks about all of them before you sign.

1. It hides what is behind it. Once a cavity is full of closed-cell foam, nobody is ever looking at that sheathing again, and water that gets in cannot dry inward. That is fine if the water management outside is right. It is a disaster if it is not. Which is why I care more about the water-resistive barrier and flashing details than about the insulation — see the best water-resistive barrier for cold-climate Idaho builds and my honest Huber ZIP System review.

2. Installation quality varies more than with any other material. Spray foam is mixed on site, in a truck, at whatever temperature the day gives you. Off-ratio foam can shrink, pull away from framing, smell, or fail to cure. There is no way to inspect a bad batch after drywall. You are buying the installer, not the product.

3. Thickness per pass is limited, and the schedule has to respect it. Closed-cell spray foam goes on in controlled lifts with cure time between them. A crew rushing to beat the drywall truck is how you get foam that shrinks off the stud face in year two.

4. The chemistry changed, and so did the pricing. The industry moved closed-cell spray foam off HFC blowing agents onto low-global-warming HFO agents. Per the Spray Polyurethane Foam Alliance, manufacturing HFC closed-cell systems has been banned nationwide since January 1, 2025, and selling or applying older HFC stock ends January 1, 2028. The HFO products also changed spray technique, pass thickness and wait times. Practically, that means a 2026 foam quote is not comparable to a 2023 one, and an installer who has not retrained on the new formulations is a risk. If a bid looks oddly cheap, ask what product and what blowing agent.

Do I need a vapor barrier behind the drywall?

In climate zone 6, yes — some form of one. The IRC requires a Class I or Class II vapor retarder on the interior side of frame walls in climate zones 5, 6, 7, 8 and Marine 4. Kraft-faced batts and vapor-retarder primer are the common Class II answers. Sheet polyethylene is Class I, and I avoid it, because it lets the wall dry in exactly zero directions.

The useful exception: a Class III retarder — ordinary latex paint — is permitted in zone 6 if the wall has either vented cladding over the sheathing, or continuous exterior insulation of at least R-7.5 over a 2×4 wall or R-11.25 over a 2×6 wall. That is the same exterior insulation layer I argued for above, and this is the second reason to install it. Enough warmth outside the sheathing means the sheathing never gets cold enough to condense, so the wall can dry to the inside through the paint.

Where closed-cell spray foam is involved, the foam itself is the vapor retarder. At roughly an inch and a half to two inches it reaches Class II, which is why you do not put poly over it, and why a flash-and-fill assembly — a couple of inches of closed-cell spray foam against the sheathing, cavity filled with cellulose or batts — handles air sealing, vapor control and R-value in one wall without a plastic sheet in it.

A note on terms, since they get mixed up constantly. A vapor retarder slows water vapor diffusing through a material. An air barrier stops air carrying moisture through holes. They are different jobs, and air leakage moves far more water than diffusion ever will. Get the air barrier right first.

Can I insulate at the roofline instead of the attic floor?

Yes, and on a vaulted-ceiling mountain house you often have to. But an unvented roof assembly in zone 6 has a specific code requirement that gets missed, and when it gets missed the sheathing rots.

Under IRC R806.5, if you insulate an unvented roof with air-permeable insulation in the rafter bays — cellulose or batts — you must also install air-impermeable insulation directly above or below the roof sheathing, at a minimum of R-20 in climate zone 6. That R-20 is not there for energy. It is there to keep the underside of the sheathing above dew point so winter moisture does not condense on it. The code table runs R-15 in zone 5, R-20 in zone 6, R-25 in zone 7 and R-30 in zone 8. The same section adds that in zones 5 through 8, any air-impermeable insulation used has to be a Class II vapor retarder or carry a Class II coating in contact with its underside.

The simpler compliance path, and the one I use, is all closed-cell spray foam against the underside of the roof deck to the full required R-value. One material, no condensation plane, no layered calculation to get wrong. It is expensive. On a vault over a great room with 85 to 100 psf of ground snow load sitting on it, it is also the assembly I trust.

If the ceiling is flat, vent the attic and blow it deep. Unvented roofs are for geometry you cannot vent, not a default.

What do we check before drywall covers the insulation?

Five things. R-value is not what keeps a house warm in Teton Valley. Air sealing and full cavities are. Our standard wall gets 1 inch of closed-cell urethane foam against the sheathing first, then dense-pack cellulose to fill the rest of the cavity. Before the drywall crew is scheduled, these five get checked and photographed.

1. 1 inch of urethane foam on every wall. The foam layer is the air barrier. One missed stud bay is a cold stripe on the drywall every January.
2. Foam sealed at every penetration. Wires, pipes, vents and boxes all get foamed where they pass through the wall. This is where most of a house’s air leakage lives.
3. Cellulose fills every cavity. Dense-pack cellulose is blown in behind netting until the bay is full and firm. A cavity that is half full insulates like a cavity that is empty.
4. No sag at the top of the wall. Cellulose settles if it is packed loose. We check the top of every bay for a gap before the netting is covered.
5. Baffles clear at every eave. The attic has to breathe. Baffles keep insulation from blocking the soffit vents, and a blocked soffit is the start of an ice dam.

The county’s insulation inspection checks that the required R-value is present. It does not check whether the cavities are full or the penetrations are sealed. That is why this list exists.

What does insulation cost, and what is not in that number?

The market ranges in the comparison table above are per square foot of insulated surface — wall area, attic area, crawl wall area — not floor area of the house. That distinction trips up almost everyone pricing this themselves. A 4,000 SF house has far more than 4,000 SF of insulated surface once you count walls, attic, rim and foundation.

What those market numbers do not include:

• Air sealing before insulation. Caulking and foaming every top plate, penetration, bottom plate and window buck is labor that happens before any insulator shows up. It is a line item and it is the one that moves the blower-door number.
• Exterior continuous insulation. Rigid or mineral wool board outside the sheathing also means longer fasteners, furring strips, deeper window bucks and different trim details. It is a wall-assembly decision, not an insulation upgrade.
• Mechanical ventilation. The HRV or ERV a tight house needs, plus its ducting and commissioning.
• Baffles, dams and blocking. Eave baffles, attic access dams, fire blocking, and the barriers around chimneys and flues where foam has to stay clear of heat sources.
• Blower-door testing. Pay for it on every house, not on a 20% sample.

For whole-project budgeting: a SwagerBuilds custom home in Teton Valley and eastern Idaho starts at $400 per square foot and goes up, and in Jackson Hole starts at $1,000 per square foot and goes up. Where a specific build lands depends on the site, the design and the finish level, which is exactly what the design phase is for. Design work is covered by a fixed design fee, quoted per project. If you want the regional cost picture, it is in what you actually pay per square foot in Teton Valley.

What do I actually spec on a SwagerBuilds house?

Here is the default, which gets adjusted for the site and the design but rarely by much:

Where	What goes in	Instead of
Rim joists	2–3 in. closed-cell spray foam	Cut-and-stuff batts
Crawl / basement walls	R-15 closed-cell spray foam or rigid board on the concrete	Fiberglass against concrete
Above-grade walls	R-21 cavity plus R-5 to R-10 continuous exterior	R-22 cavity only
Vented attic	R-60 blown-in, baffled eaves, sealed penetrations	R-49 and call it good
Vaults / unvented roof	Full-depth closed-cell spray foam to code R-value	Batts with an undersized foam layer
Interior partitions	Mineral wool at bedrooms, baths, laundry, mechanical	Empty cavities
Verification	Blower door on every house, number given to the owner	Sample testing

Where a house is in a wildfire-exposed spot, mineral wool moves from the interior partitions to the exterior walls and the eaves, because it does not burn — that reasoning is in wildfire resistant home construction in Idaho. Where we are sealing a crawl space tight, the radon rough-in goes in at the same time, because both are cheap during construction and expensive after; that is the radon mitigation post. And if you are weighing certification, whether a green custom home is worth it covers what the labels actually buy.

I am involved in every phase of every build, and insulation day is one I show up for. Not because I am holding the gun — the foam crews and insulators do that work, and the good ones are better at it than I would be — but because that is the last day the wall is open. Once drywall is on, every shortcut is permanent.

How do I know the installer did it right?

Four checks, and you can do all of them yourself.

Walk the house before drywall. Batts should be cut to fit, split around wiring rather than crushed over it, and fully touching the back of the sheathing with no gaps at the edges. Blown attic insulation should be level to a marked depth ruler, not drifted. Spray foam should be trimmed flush to the studs with no voids behind it and no shrinkage gaps at the framing.

Ask for the blower-door result for your address. A number, in ACH50, on paper. If the answer is that the builder tests a sample of houses, you are not getting a measurement of yours.

Ask what the insulation inspection found. There is a code inspection for this, before cover. It is in the normal sequence I lay out in what inspections happen when you build a custom home.

Ask for the product data sheets. Brand, R-value per inch, installed thickness, and for foam, the blowing agent. A builder who cannot produce that is guessing, and guessing is how you end up with a wall that misses the vapor rule.

The broader point: insulation is a trust question, not a product question, which is the same argument I make in whether a premium custom home builder is worth it. You cannot verify it after the fact, so you verify the builder before.

Frequently asked questions about spray foam and insulation

Is spray foam worth it for a whole house in Idaho?
Usually not for every cavity. Closed-cell spray foam is worth it at rim joists, crawl and basement walls, unvented roofs and hard-to-seal details, where it buys air sealing and moisture control you cannot get another way. For open wall cavities and vented attics, blown-in insulation behind a good air barrier gets you the same R-value for less money, and the savings are better spent on continuous exterior insulation and windows.

How much insulation does Idaho code require?
Idaho enforces the 2018 IECC with amendments, effective January 1, 2021. In climate zone 6, which covers eastern Idaho and Teton Valley, that is R-49 ceilings, R-22 walls or R-13 plus R-5 continuous, R-30 floors, and R-19 or R-15 continuous at basement and crawl space walls. Blower-door testing is required on a minimum 20% sample of each builder’s homes rather than every house.

Can spray foam cause moisture problems in a cold climate?
Closed-cell spray foam itself is a vapor retarder, so it does not get wet. The risk is that it prevents a wet assembly from drying inward, so if water gets past the siding and water-resistive barrier it has nowhere to go. That makes exterior water management and flashing more important on a foamed wall, not less. Open-cell foam is vapor open and needs a separate interior vapor retarder in climate zone 6.

What R-value do I need for an unvented vaulted ceiling?
Under IRC R806.5, if air-permeable insulation fills the rafter bays, you also need air-impermeable insulation above or below the roof sheathing at a minimum of R-20 in climate zone 6 for condensation control. Zone 5 is R-15, zone 7 is R-25 and zone 8 is R-30. The simpler path is all closed-cell spray foam against the roof deck to the full required R-value.

Does a tight house need mechanical ventilation?
Yes. Once a house is air sealed, it cannot rely on leaks to bring in fresh air, so a balanced heat-recovery or energy-recovery ventilator belongs in the mechanical design from the start. Air sealing without ventilation is how you get stale air and high indoor humidity. Budget both together, not as a change order.

Want this done right on your build?

If you are planning a custom home in Teton Valley, Jackson Hole or eastern Idaho and want the envelope engineered rather than bid to the lowest number, that conversation happens in the design phase — plans, structural and mechanical engineering, and the assembly decisions all together, before anyone quotes construction. SwagerBuilds handles that whole path in-house, from drawings through engineering coordination to keys. Call (208) 520-0636 or tell me about your project.

Built different. Built right. Built by SwagerBuilds.

TL;DR: Triple pane windows are worth it in Idaho on the walls you actually live against — big view glass, north and west exposures, bedrooms, and any room with a seat next to the window. On small, sheltered openings the upgrade buys you very little. The comfort gain shows up immediately; the energy savings take years. Decide it on the window schedule during design, not after the walls are framed.

I have been building in eastern Idaho and Teton Valley for 20 years, and windows are the single most argued-over line on a custom home. They are also the one thing on the drawings that is permanent. You can change a countertop in year six. You are not re-glazing a 30-foot view wall because the room turned out cold.

So here is the honest version of the triple pane question, with the numbers that actually drive it and the places where I tell clients to save their money.

What are triple pane windows, and how are they different from double pane?

A double pane window has two sheets of glass with a sealed gap between them, usually filled with argon gas. A triple pane window adds a third sheet and a second gap. That is the whole idea: one more layer of still gas between you and a January morning.

The third pane is not really about the glass. It is about the two insulating cavities and the extra low-emissivity coating, a microscopically thin metal layer that reflects heat back toward the side it came from. More cavities and more coatings mean less heat leaving the room.

The trade-off is weight. A triple pane sash can run half again as heavy as a double, which is why the hardware, the hinges and the frame have to be built for it. This is also why a cheap triple pane window from a manufacturer that mostly builds doubles is often worse than a good double.

Are triple pane windows worth it in Idaho? The short answer

Yes on the glass you live against. No on the glass you walk past.

Teton Valley, Driggs, Victor, Tetonia, Rexburg and most of the upper Snake River plain sit in climate zone 6, the second-coldest zone in the lower 48. Design temperatures here run well below zero. In that climate the difference between a code-minimum window and a good triple pane window is not an abstraction on a utility bill. It is whether the sofa under the window is usable in February.

The reason is surface temperature. A window’s interior glass surface sits somewhere between room temperature and outdoor temperature depending on how well it insulates. On a code-minimum double pane unit at 10 below, that inside surface gets cold enough that you feel your own body heat radiating toward it. People describe it as a draft. There is no draft. You are the draft.

A good triple pane window raises that interior surface temperature by a meaningful margin. The room feels even, the cold pool along the floor under the window mostly disappears, and the condensation that fogs the bottom corners on the coldest mornings stops showing up. That is the real product you are buying. The heating savings are a bonus that arrives slowly.

What do the numbers on a window sticker actually mean?

Every window carries a label from the National Fenestration Rating Council with four or five numbers on it. Manufacturers will quote you the one that flatters them. Here is what each one does.

U-factor is how fast heat escapes through the whole window, frame included. Lower is better. This is the number that matters most in a cold climate, and it is the one code regulates.

Solar Heat Gain Coefficient (SHGC) is how much of the sun’s heat comes through, on a 0 to 1 scale. In hot climates you want it low. In zone 6 you generally want it reasonably high on south-facing glass, because free winter sun is worth having, and lower on west glass, which cooks in July afternoons.

Visible Transmittance (VT) is how much light comes through. Stacking low-e coatings to chase a low U-factor can drag VT down, and a house full of gray-looking glass is a permanent mistake. I would rather give up a couple hundredths of U-factor than live behind tinted-looking windows with a Teton view on the other side.

Air Leakage is how much air the assembly passes. Lower is better and almost nobody checks it.

Condensation Resistance runs 1 to 100, higher is better, and it is the number I actually care about in Teton Valley. It predicts whether the bottom of your glass will sweat and eventually stain the stool and jamb.

What does Idaho code require for windows?

Idaho enforces the 2018 IECC with state amendments, effective January 1, 2021, per the U.S. Department of Energy’s state code status page. In climate zone 6, the prescriptive path caps window U-factor at 0.30 and does not regulate SHGC.

Read that carefully: U-0.30 is the worst window you are legally allowed to install. It is a floor, not a target. A decent double pane unit clears it. Nothing about meeting code means the house will feel good.

For comparison, ENERGY STAR Version 7.0 sets the Northern zone bar at U-0.22 or lower with an SHGC of 0.17 or higher, with equivalent-performance paths that allow a slightly higher U-factor in exchange for more solar gain. You can read the current criteria on the ENERGY STAR windows and doors page. Most cold-climate builders specifying triple pane windows land somewhere in the U-0.17 to U-0.26 range documented by GreenBuildingAdvisor.

So the honest gap is this: code says 0.30, a good triple pane window says roughly 0.20, and the difference between those two numbers is about a third of the heat loss through every square foot of glass in the house.

Where the upgrade pays for itself, and where it doesn’t

I do not spec triple pane windows across the whole house on every build, and any builder who tells you it is all-or-nothing is selling a package rather than solving your problem. Here is how I sort it.

Opening	My call	Why
Great room view wall, large fixed glass	Triple, every time	Biggest area, most heat loss, and it’s where people sit. This is the whole ballgame.
North and west elevations	Triple	North gets no solar gain to offset the loss. West takes the wind and the winter weather.
Bedrooms, especially on an exposed corner	Triple	People sleep next to this glass. Cold radiant surfaces wreck sleep more than cold air does.
South-facing glass under a deep overhang	Either, lean triple if the opening is large	Winter sun offsets some loss, so a high-SHGC double can pencil. Size decides it.
Small bath, pantry, laundry, stair windows	Double is fine	Little area, nobody lingers. Spend the money elsewhere.
Garage and unconditioned space	Double	Not heated. Don’t overthink it.
Egress windows in a basement bedroom	Size for code first, glazing second	The opening dimensions are non-negotiable. See our Idaho egress window requirements.

The pattern is simple. Triple pane windows earn their money where the glass is big, the exposure is harsh, or a human being sits still nearby. Everywhere else, a well-built double pane unit with a good frame and a clean install does the job.

Double pane vs triple pane: a side-by-side

	Code-minimum double	High-performance double	Triple pane
Typical U-factor	Around 0.30	Roughly 0.24 to 0.28	Roughly 0.17 to 0.26
Meets Idaho zone 6 code	Yes, barely	Yes	Yes, with room to spare
Meets ENERGY STAR v7 Northern	No	Sometimes, via the equivalent-performance path	Usually
Interior glass temperature at 10 below	Coldest	Noticeably better	Best by a clear margin
Condensation on cold mornings	Common at bottom corners	Occasional	Rare
Sound from the road or the wind	Baseline	Slightly better	Better, especially with uneven glass thicknesses
Sash weight and hardware demand	Standard	Standard	Heavier, needs hardware built for it
Visible light	Highest	High	Slightly lower, varies by coating package
Where I use it	Nowhere by choice	Small and sheltered openings	View walls, bedrooms, north and west

Notice the middle column. A high-performance double pane window from a manufacturer that builds serious cold-climate units will beat a bargain triple from a company that bolted a third pane onto a builder-grade frame. The label on the box is not the spec. The NFRC number is the spec.

What does the triple pane upgrade cost?

I am not going to hand you a per-window number, because it would be wrong by the time you read it and wrong again for your particular window schedule. What I can tell you is how the cost behaves.

The upgrade is priced as a percentage of the window package, not the house. Window packages scale with glass area, so a house with a 30-foot view wall and a wall of sliders feels this decision hard, and a house with conventional punched openings barely notices it. As one data point, a builder case study published on GreenBuildingAdvisor put the triple pane upgrade at roughly $4,100 on a $30,000 window order, about 14 percent. Treat that as third-party market data from another project, not a SwagerBuilds quote.

Three things move the number more than the third pane does:

• Frame material and manufacturer tier. The jump from a mid-tier line to a premium line usually costs more than the jump from double to triple within the same line.
• Glass area. Fixed picture units are cheap per square foot. Operable units, big sliders and lift-and-slide doors are not.
• Custom sizes and shapes. Every non-standard unit carries a premium, and mountain-modern elevations are full of them.

On a SwagerBuilds project the window schedule gets priced inside the design agreement, before you sign a construction contract, so the glazing decision is made against a real number instead of a guess. Our construction pricing starts at $400 a square foot and goes up on the Teton Valley and Idaho side, and starts at $1,000 a square foot and goes up in Jackson Hole. Design itself is a fixed design fee, quoted per project. For how the window allowance behaves inside a contract, see how construction allowances work and why three bids don’t compare. The window line is one of the most common places two bids quietly differ.

Does the frame matter more than the glass?

Often, yes. The U-factor on the NFRC label is a whole-window number, which means a great glass unit in a bad frame reports a mediocre result. Here is how the common frame materials behave in our climate.

Frame	Thermal performance	What to watch
Fiberglass	Excellent	Expands and contracts at nearly the same rate as glass, so seals last. My default for harsh exposures.
Vinyl	Good	Fine thermally, but wide frames eat glass area and cheap lines sag on large units. Quality varies enormously.
Aluminum-clad wood	Good	The look most Teton Valley clients want. Requires disciplined flashing, since the cladding hides what is happening underneath.
Wood, unclad	Good	Beautiful inside. Exterior maintenance in this climate is real work. I steer clients away for exposed elevations.
Thermally broken aluminum	Fair to good	Works for big modern openings where nothing else spans. Verify the thermal break is rated, not decorative.
Standard aluminum	Poor	Conducts cold straight through. Not a zone 6 product.

Frame choice also interacts with the wall. On a house with continuous exterior insulation, the window has to be set out from the structural sheathing, which changes the flashing detail and the buck construction. That is a drawing decision, not a field decision. We work it out with the wall assembly during design, alongside the weather-resistive barrier and the siding system.

Is there still a tax credit for efficient windows in 2026?

No. The section 25C energy efficient home improvement credit, which covered up to $600 a year for qualifying windows, was terminated for property placed in service after December 31, 2025. The IRS spells this out in its FAQ on the 2025 law changes. The related section 45L new-home credit ended for homes acquired after June 30, 2026.

So if you were counting on a federal credit to close the gap on triple pane windows, that math is gone. Decide the upgrade on comfort and on how long you plan to own the house, not on a rebate. We covered the same shift in our post on whether a green custom home is worth it.

What goes wrong with windows on a mountain build?

In 20 years the failures I see almost never trace back to the glass package. They trace back to four things.

Installation. A premium window set in a sloppy rough opening is a premium leak. The sill pan, the back dam, the sequencing of the flashing against the housewrap, and the air seal on the interior side all have to be right, in that order. Sequencing is what separates a dry wall from a warranty claim in year four.

Snow and grade. Window sills set too low relative to the finished grade and the drift line get buried. Buried sills stay wet. We set sill heights against the actual snow reality on that lot, not against the plan’s elevation drawing.

Interior humidity. A tight house with no balanced ventilation will condense on its windows no matter how good they are. If a house is built to modern airtightness and gets no mechanical fresh air, the glass becomes the coldest surface and takes all the moisture. That is a ventilation problem wearing a window costume. See the ventilation section in our energy efficient custom home features post.

Ordering late. Window lead times on custom sizes and premium lines routinely run months. A window order placed after framing starts is how a house sits wrapped in plastic through a Teton Valley November. The schedule is set by the longest lead item, and it is usually the windows.

How I spec windows on a custom home

The window schedule is settled during the design agreement, before anybody signs a construction contract. That is deliberate. Glazing drives the heating load, the heating load drives the mechanical design, and the mechanical design drives duct routes and soffits. Change the windows in month four of construction and you are re-engineering three other systems.

Here is the order I work in:

1. Orientation and views first. Where the glass goes is an architecture decision. We handle plan development and drawings in-house, so this gets resolved on paper with revisions in days, not weeks.
2. Size and quantity second. More glass than the house needs is the most expensive form of regret. I will push back on a window that exists only because the elevation looked bare.
3. Frame material third. Driven by exposure, maintenance appetite and the look the client is after.
4. Glazing package last. This is where triple pane windows get assigned opening by opening, using the table above rather than a blanket rule.
5. Install detail documented. The flashing sequence goes on the drawings and gets verified in the field, not left to whoever is on the wall that day.

Then it gets priced and locked into a fixed construction contract. No allowance games on the window line, because that line is too big to leave floating. If you want to see how the whole design phase runs, we wrote it up in getting a real number before you sign, and the broader upgrade question in which custom home upgrades are actually worth the money.

If you are planning a build in Teton Valley, Driggs, Victor, Rexburg, Rigby or the Idaho Falls area and want the window package sorted before it becomes a change order, start the conversation here. Built different. Built right. Built by SwagerBuilds.

Frequently asked questions

Are triple pane windows worth it in Teton Valley?
On large glass, north and west exposures, and bedrooms, yes. Those are the openings where the colder interior glass surface of a double pane unit is something you feel every winter. On small, sheltered windows the upgrade is hard to justify and the money does more good in insulation or air sealing.

How much energy do triple pane windows actually save?
Less than most people expect, and the payback on energy alone is usually measured in decades rather than years. The reason to buy them in climate zone 6 is comfort, even room temperatures and the end of winter condensation. Treat the utility savings as a small bonus.

What U-factor should windows have in Idaho?
Idaho’s 2018 IECC-based code caps zone 6 windows at U-0.30, which is a legal minimum rather than a good target. ENERGY STAR Version 7.0 asks for U-0.22 or better in the Northern zone, and most cold-climate triple pane windows land between roughly 0.17 and 0.26.

Do triple pane windows stop condensation?
They dramatically reduce it, because the interior glass stays warmer. They do not fix a house with no balanced ventilation and high indoor humidity. If a tight home has no HRV or ERV moving fresh air, moisture will still find the coldest surface in the room.

Can I mix double and triple pane windows in the same house?
Yes, and on most of my builds we do. Manufacturers build both within the same product line, so the sightlines, colors and hardware match. Put the triple pane windows where the glass is large or the exposure is harsh, and spend the savings on the openings nobody sits beside.

TL;DR: Basement vs crawl space vs slab is really a question about three things: how deep your footings have to go anyway, what the dirt under your lot will let you do, and how much usable square footage you want for the money. In Teton Valley and most of Eastern Idaho the frost line already forces the concrete most of the way down, so a basement is cheaper here, relative to the alternatives, than it is almost anywhere else in the country. That is why I build basements on most custom homes, conditioned crawl spaces when the water table or the rock says no, and slab-on-grade only in a handful of specific situations.

Basement vs crawl space vs slab: which one should you build?

Here is the short version, then the reasoning. On a custom home in Teton Valley, Driggs, Victor, Rexburg, Rigby or Idaho Falls, a full basement is usually the best dollar-per-square-foot buy on the whole project. A conditioned crawl space is the right answer when groundwater, rock or a steep lot makes a basement expensive or impossible. A slab-on-grade is the right answer on a small number of lots where the soil is good, the water is high, and the client genuinely does not want the extra space.

What makes the basement vs crawl space debate different in Idaho than it is in Texas or Arizona is that we are not choosing whether to put concrete in the ground. The code already decided that. We are only choosing what to do with the hole we are required to dig.

What does frost depth have to do with my foundation?

Frost depth is the depth the ground can freeze to in a hard winter. Footings have to sit below it, because soil that freezes swells, and soil that swells lifts concrete. Lift a footing an inch and you crack a foundation wall, rack a door, and split drywall two floors up.

Two real numbers from the counties we build in. Teton County, Idaho requires 32 inches measured from the bottom of the footing to finished grade, along with a ground snow load of 85 psf below 6,600 feet and 100 psf at 6,600 feet and above, seismic design category D-1, and 115 mph wind. The City of Idaho Falls publishes 30 inches from finished grade to the bottom of the footing, a ground snow load of 47.1 psf derived from the city’s 4,710-foot elevation, seismic design category D when soils are unknown, and a 115 mph ultimate wind speed.

Read that again with a tape measure in your head. You are already digging two and a half to three feet down and pouring a footing and a stem wall to get there. A crawl space adds a little more depth. A basement takes that same wall to roughly eight feet and gives you a floor. The concrete and the excavator are already on site either way, and that is the entire economic argument for a basement in this climate.

What does each foundation actually cost?

I am not going to hand you a per-square-foot menu for a SwagerBuilds foundation, because the foundation is not sold separately. A SwagerBuilds custom home starts at $400 per square foot and goes up in Teton Valley and Eastern Idaho, and starts at $1,000 per square foot and goes up in Jackson Hole. What the foundation does is move where you land inside that.

What I can give you is third-party market data so you can see the relative spread. These are national figures published by HomeGuide for 2026, not SwagerBuilds pricing, and they run low for mountain work with engineered footings and deep frost protection:

Foundation type	Market cost range (national, 2026)	Usable space added	Where it fits in Eastern Idaho
Monolithic slab	$6 to $14 per sq ft	None	High water table, flat lot, single-level program
Stem wall with slab	$6 to $18 per sq ft	None	Where frost depth is required but no under-floor space is wanted
Crawl space	$15 to $18 per sq ft	Mechanical and storage only	Rock, high groundwater, steep or tight sites
Full basement, unfinished	$35 to $50+ per sq ft	Full floor of the house	Most Teton Valley and Eastern Idaho custom homes
Finishing a basement later	Adds $30 to $50 per sq ft	Converts storage to living space	Common phase-two move

Here is the part most builders skip. Compare the basement line to the whole-house number, not to the crawl space line. If a finished square foot of your main floor is priced from $400 and goes up, and unfinished basement square footage lands in the range above with finishing later in its own range, the basement is the cheapest square footage you will ever add to that house. It is the only place on the project where you buy floor area at a discount instead of a premium.

For how the rest of the number comes together, see our full breakdown of what it costs to build a custom home in Idaho.

When does a basement make sense in Idaho?

Most of the time, here. The frost depth argument above does most of the work, but there are three more reasons I push clients toward a basement when the site allows it.

Mechanical space. A mountain house at 6,000 feet carries a lot of equipment: boiler or furnace, hot water, HRV or ERV, water treatment if you are on a well, a snowmelt manifold if you have one. Putting that in a basement room instead of a closet on the main floor buys back main-floor square footage you were paying full price for.

Guest and kid space you do not heat year round. A basement stays within a few degrees of ground temperature on its own. It is the cheapest space in the house to condition and the easiest to shut down when nobody is in it, which matters a lot on second homes.

Walkout potential. On any lot with grade, a walkout basement turns below-grade square footage into real daylight living space with windows and a door. That is the single best value move in mountain custom home building and it costs almost nothing extra when the slope is already there.

One rule you cannot skip: any basement bedroom needs a compliant emergency escape opening. We cover the sizes and sill heights in our guide to egress window requirements in Idaho. Plan the window wells at design, not at framing, because retrofitting one through a finished foundation wall is ugly and expensive.

When is a crawl space the right call?

Four situations put us in a crawl space instead of a basement: groundwater within a few feet of the planned basement floor, rock or hardpan that turns excavation into blasting, a lot too steep or too tight to get the dirt out economically, and a client who simply does not want the space and will not pay for it.

When we do build one, it is a closed, conditioned crawl space, not a vented one. This is not a preference, it is building science. Building Science Corporation’s work on vented versus closed crawl spaces lays out the failure mode clearly: put fiberglass batts between the floor joists and vent the space, and the underside of that insulation ends up within a degree or two of ground temperature. Humid air enters through the vents, hits those cold surfaces, and condenses. Wood has to stay below 19 percent moisture content to never rot and below 16 percent to never grow mold, and a vented crawl space in a humid stretch does not reliably hold either line.

A conditioned crawl space is built as a short basement instead. Sealed vapor barrier across the whole soil floor and up the walls. Insulation on the perimeter walls, not in the floor joists. The space is inside the building envelope and gets air from the house. It stays dry, the ductwork and pipes in it are inside conditioned space, and the floor above it is not cold in February.

A crawl space still changes how the floor system gets designed. The span, the beam layout and the post locations all shift depending on what is under them, which is why we settle it in design. See our comparison of TJI joists versus floor trusses for how that plays out.

When does a slab-on-grade actually work here?

Rarely, and I will tell you straight that I talk most clients out of it in Teton Valley. A slab makes sense when the water table is genuinely high, when the program is single-level and the client wants it that way, when the lot is flat enough that a slab does not require a mountain of imported fill, and when radiant floor heat is central to the design. A slab is a very good host for radiant tubing.

What you give up is everything below the floor. Every mechanical run, every plumbing line, every future change is now in the concrete or in the walls. Changing a drain line after the pour means a saw and a jackhammer. On a house you intend to keep for thirty years, that lack of access is the real cost, not the concrete.

And in a climate with a 30 to 32 inch frost requirement, a slab does not save you the footing. You still pour a frost wall around the perimeter. You pay for most of the depth and get none of the space.

Does the basement vs crawl space choice change my radon plan?

Yes, and this is where the basement vs crawl space decision gets practical. Eastern Idaho and Teton Valley sit in an area where elevated indoor radon is common, and the fix is dramatically cheaper before the concrete goes down than after.

On a basement, a passive radon rough-in means a layer of clean gravel under the slab, a sealed membrane, a tee in the gravel, and a pipe stubbed up through the roof. On a conditioned crawl space, the sealed soil vapor barrier you are installing for moisture control is most of the radon system already, and the pipe ties into the same space beneath it. On a slab, it is the same sub-slab approach as a basement. In all three, the rough-in happens during the foundation stage or it does not happen cheaply at all. We walk through the whole thing in our post on radon mitigation in a new Idaho home.

The same logic runs through the rest of the envelope. Foundation insulation, under-slab insulation and the air seal at the sill plate are all decisions made at this stage and expensive to revisit, which is why they show up in our list of energy efficient custom home features worth paying for.

What does the foundation do to resale?

In this market, a finished or finishable basement is an asset buyers look for and a crawl space is neutral. I have never had a buyer’s agent flag a conditioned crawl space as a problem when it is dry and properly built. I have had plenty of buyers in Teton Valley skip a house because there was nowhere to put gear, guests or a shop bench.

A slab is the one that costs you on resale here, and not because buyers dislike slabs in the abstract. It is because a $1M to $5M mountain home without any below-grade space reads as a smaller house than it is. The square footage is all priced at finished rates and there is no cheap space to absorb the overflow.

That said, do not build a basement you do not want purely for resale. If the program genuinely does not need it and the lot fights you, the right answer is the crawl space. We work through this kind of trade-off in our post on which custom home upgrades are actually worth the money.

What is not included in a foundation number?

Any time you see a foundation figure, from us or anyone else, ask what sits outside it. On a typical Eastern Idaho or Teton Valley lot, these are the items that live next to the foundation line and get forgotten:

• A geotechnical soils report where the county or the engineer requires one, and any engineered fill or over-excavation it calls for.
• Rock excavation, which is priced separately for a reason, and hauling spoils off site when there is nowhere to spread them.
• Foundation drainage: perimeter drain, filter fabric, drain rock, and somewhere for the water to actually go.
• Damp-proofing or full waterproofing on the exterior of a basement wall, which are not the same product or the same price.
• Under-slab insulation, under-slab vapor barrier, and the radon rough-in described above.
• Window wells, well covers and their drainage on any basement bedroom.
• Backfill, final grade away from the house, and the driveway and utility trenching that has to be coordinated with it.

Site work is the single most under-budgeted line on custom home projects in this valley. If your lot is raw, read our guide to how to prepare land to build a house and our numbers on well and septic costs in rural Idaho before you set a budget.

How we make this call on a SwagerBuilds build

We settle the foundation during the design agreement, before there is a construction price to sign. That order matters. The foundation drives the floor plan, the floor plan drives the structure, and the structure drives the number. Deciding this after plans are drawn means redrawing plans.

The sequence looks like this. We walk the lot and look at grade, drainage and where the water goes in spring. We get soils information when the site or the county calls for it. We coordinate the structural engineer on footing sizes for snow load and seismic category, which in Teton County means designing to 85 or 100 psf ground snow and seismic D-1. We draw the foundation with the plan set, not after it. Then we price the build against a foundation that is actually designed rather than assumed.

I have been in construction for 20 years and I am involved in every phase of every build, from that first walk on the dirt through the final walkthrough. We handle the plan development, the architectural drawings, the engineering coordination and the permitting in-house or through people I have worked with for years, under a fixed design fee quoted per project. You do not have to go assemble a team to answer this question. That is our job.

Every SwagerBuilds job also runs 24/7 site cameras, so you can watch the footings go in from wherever you are. For what happens after the concrete, see our walkthrough of the inspections on a custom home build, and if you are still at the plan stage, start with custom house plans for Teton Valley and Eastern Idaho.

Thinking about a build in Teton Valley, Jackson Hole or Eastern Idaho? Bring me your lot and your program and I will tell you straight which foundation it wants and why. Call SwagerBuilds at (208) 520-0636 or apply to work with us.

Built different. Built right. Built by SwagerBuilds.

Frequently asked questions

Is a basement cheaper than a crawl space in Idaho?

Not per square foot of foundation, but it is cheaper per square foot of house. Because Idaho frost depth requirements already push footings 30 to 32 inches below grade, most of the excavation and the concrete wall are required regardless. A basement extends that wall and adds a floor, so you buy usable square footage at a fraction of what finished main-floor space costs.

Do I need a vapor barrier in a crawl space in Idaho?

Yes. We build closed, conditioned crawl spaces with a sealed vapor barrier across the entire soil floor and lapped up the walls, with insulation on the perimeter walls rather than in the floor joists. A vented crawl space with batts between the joists is the assembly that rots floor framing in this climate.

Can you build a basement if the water table is high?

Sometimes, with engineered drainage and full waterproofing, but it gets expensive fast and the risk never goes to zero. When groundwater sits close to the planned basement floor, we usually recommend a conditioned crawl space instead. That decision is made from actual site information, not a guess, which is why we look at soils and spring drainage during design.

How deep do footings have to be in Teton Valley?

Teton County, Idaho requires 32 inches measured from the bottom of the footing to finished grade, or as determined by a soils investigation. Idaho Falls requires 30 inches. Both counties also carry significant snow and seismic loads, so footing size is engineered per project rather than taken from a table.

Does a slab foundation hurt resale value on a custom home?

In the Teton Valley and Eastern Idaho market it usually does, not because buyers object to slabs but because a home with no below-grade space offers no inexpensive storage, mechanical or guest area. Buyers in this price range expect somewhere to put gear. On a flat lot with a high water table and a single-level program, a slab can still be the right build.

Short answer: radon mitigation is not required by code in Idaho, but two out of five Idaho homes test above the EPA action level, so I rough in a passive radon system on every house I build. It is cheap while the foundation is open and expensive once the slab is poured. Test after you move in, then add a fan only if the number says to.

What is radon, and why should I care in Idaho?

Radon is a radioactive gas that comes out of the ground as uranium in soil and rock breaks down. You can’t see it, smell it, or taste it. It seeps up through soil and collects inside a house, and the only way to know your number is to test for it.

It matters because the Idaho Department of Health and Welfare reports that two out of five Idaho homes have elevated radon levels. That is not a scare statistic from a company selling fans. That is the state health department describing the ground we build on.

The EPA’s action level is 4.0 pCi/L. At 4.0 or above, you fix it. Between 2.0 and 3.9, the state says consider fixing it. Below 2.0, you’re in good shape. Those are the only three numbers you need to hold onto.

Do I need radon mitigation in a new home?

Nobody can tell you that you need radon mitigation before the house exists, because radon is measured in a finished, closed-up building. A soil test on an empty lot won’t give you a reliable answer. Anyone who quotes you a mitigation system off a vacant lot is guessing.

So the honest answer is this: you don’t know yet, and that’s exactly why you rough it in. The parts of a radon system that are painful to add later are the parts that go in while the ground is open and the slab isn’t poured. The part you might never need is a fan, and a fan takes an afternoon.

That’s the whole decision. Spend a little now so that the expensive version never becomes necessary. I’ve been in construction 20 years, and this is one of a very short list of items where the build-stage version and the retrofit version aren’t even close in cost or in quality of result.

Is radon actually a problem in Teton Valley and eastern Idaho?

Yes, and the EPA’s own mapping says so. The EPA Map of Radon Zones sorts every county into Zone 1 (highest predicted potential), Zone 2, or Zone 3. Here’s how the counties I build in land:

County	EPA radon zone	Towns I build in
Teton	Zone 1 (highest)	Driggs, Victor, Tetonia
Madison	Zone 1 (highest)	Rexburg
Bonneville	Zone 1 (highest)	Idaho Falls, Ammon
Fremont	Zone 1 (highest)	Island Park, St. Anthony
Bingham	Zone 1 (highest)	Shelley, Blackfoot
Jefferson	Zone 2	Rigby, Menan

Read that table again. Almost every county in my service area is in the EPA’s highest radon zone. Our own shop sits in Jefferson County, which is Zone 2, and I still treat Zone 2 as a reason to rough in rather than a reason to skip it.

One thing to keep straight: a zone is a prediction about geology, not a measurement of your house. Two houses on the same road can test very differently depending on how the soil sits, how the foundation was built, and how tight the house is. The zone tells you the odds are worth taking seriously. Only a test tells you your number.

What does a radon system look like in a house that isn’t built yet?

It’s simpler than most people picture. There’s no machinery in your living space and nothing you interact with day to day. A passive rough-in is four things, and all four happen in the ground and in the walls before drywall:

• A gas-permeable layer under the slab. Clean coarse gravel under the concrete, so gas can move sideways to one collection point instead of sitting under the whole floor.
• A sealed barrier. Heavy poly sheeting over that gravel, lapped and sealed, plus caulking at the joints and penetrations where the slab meets walls and pipes.
• A vent pipe from under the slab to above the roof. Usually 3 or 4 inch PVC, teed into the gravel layer, run up through an interior wall chase and out the roof, labeled as a radon pipe at every floor.
• Power roughed in at the pipe, in the attic. An electrical junction near the vertical pipe so a fan can be added later without opening finished walls.

That’s the passive system. It works on stack effect, meaning the warm air rising in the pipe pulls soil gas out from under the slab on its own, with no fan. Sometimes that alone drops a house below the action level. If it doesn’t, the fan goes on the pipe in the attic and the system becomes active.

The EPA publishes builder drawings for exactly this, including a crawlspace version, in its radon-resistant new construction resources. The current standards it points to are ANSI/AARST CCAH-2020 for reducing radon in new homes and ANSI/AARST RRNC-2020 for roughing in the components, both effective December 1, 2023.

Crawlspace instead of a slab? Same idea, different execution. The poly goes over the crawlspace floor as a sealed membrane and the pipe pulls from under it. If you’re weighing basement against crawlspace, the radon rough-in is not the deciding factor, but it is cheaper and cleaner on a slab or a basement than on a vented crawl.

What does radon mitigation cost during the build versus after?

Here are the published figures, and I want to be clear that these are market and agency numbers, not a SwagerBuilds price list. The Idaho Department of Health and Welfare puts radon-resistant features at $300 to $500 when they go in during construction. A professionally installed system in an existing house runs $1,500 to $3,500. A do-it-yourself retrofit kit lands at $300 to $600.

Approach	When it happens	Published cost range (market data)	What you’re buying
Passive rough-in during construction	Foundation and framing	$300–$500 (Idaho DHW)	Gravel layer, sealed poly, vent pipe, power at the pipe. Hidden in the structure.
Adding a fan to an existing rough-in	After testing, any time	Fan and labor, an afternoon of work	Turns the passive system active. No finished surfaces touched.
Professional retrofit, no rough-in	After the house is finished	$1,500–$3,500 (Idaho DHW)	Core through the slab, exterior pipe, fan. Visible pipe outside.
DIY retrofit kit	After the house is finished	$300–$600 (Idaho DHW)	Homeowner labor and no performance testing unless you hire it out.

The gap in that table is the entire argument. Roughing in during construction is the cheapest line on the list, and it’s also the only one that leaves no pipe running up the outside of your house. A retrofit on a finished home means coring the slab, routing pipe along an exterior wall, and living with how that looks on an elevation you paid to get right.

For context on where this sits in a whole project: SwagerBuilds custom homes start at $400 per square foot and go up in Teton Valley and eastern Idaho, and start at $1,000 per square foot and go up in Jackson Hole. A radon rough-in is a rounding error against that. It is one of the highest-return small decisions in the entire build, which is why it shows up on my list of custom home upgrades that are actually worth the money.

Passive or active: which system do I actually need?

You need the passive rough-in. Whether you need the fan is a question your test answers after you move in, and there’s no way to know sooner.

	Passive system	Active system
How it moves air	Stack effect, no fan	Inline fan on the vent pipe
Installed when	During construction	Usually added after a test
Operating cost	None	Fan runs continuously, small draw
Noise	None	Slight, and it’s in the attic
Typical reduction	Modest, sometimes enough	Reliable, and verifiable by retest
Needs a rough-in first	It is the rough-in	Far cheaper if the rough-in exists

The practical sequence is: rough in passive, move in, test, and add the fan only if your number calls for it. If you do add one, retest afterward to confirm the system actually did its job. A fan that’s running is not the same thing as a house that’s below 4.0.

Does Idaho code require a radon system?

No. Idaho’s residential code is the 2018 International Residential Code, and the state’s amendments to it cover things like footing widths, wall bracing, ventilation, and sprinklers. Radon control isn’t in them. No building department I work with in Teton, Madison, Bonneville, or Jefferson County will fail an inspection over a missing radon system, and no inspector is going to bring it up.

That’s worth understanding clearly, because it’s easy to assume that anything important is covered by code and anything not covered must be optional fluff. Code is a floor, not a standard of care. Plenty of what makes a house good to live in sits above it. If you want the full picture of who inspects what and when on an Idaho build, I wrote that up in what custom home inspections actually happen, and the county-by-county permitting paths are on our Idaho building permits by county page.

So radon mitigation in eastern Idaho is a builder-and-owner decision, not a code compliance item. I make it the default on my builds rather than a line item you have to know to ask about. Most people don’t know to ask, and I’d rather not have that conversation in year three.

When do I test, and what happens if the number comes back high?

Test after you move in and the house is being lived in and closed up. Winter is the better season here, because the house is shut tight and the stack effect is strongest, which tends to show you your realistic high end rather than a flattering summer number.

Short-term tests run 2 to 90 days and give you a fast read. Long-term tests run past 90 days and better reflect a true annual average. If a short-term test comes back near or above 4.0, confirm it with a second test before you spend money. Idaho’s health department offers residents a free test kit every two years, and there’s a library lending program with free kits at participating public libraries, though availability moves around.

If your confirmed number is at or above 4.0 and you have a rough-in, this is an easy day. A fan goes on the existing pipe in the attic, and you retest to verify. No slab work, no exterior pipe, no patching. If your number is between 2.0 and 3.9, the state says consider mitigating, and with a rough-in already in place that decision costs you very little to act on.

What’s not included in that number?

Fair question, and one I’d want answered too. The $300 to $500 construction figure covers the rough-in materials and labor. It does not include a fan, the testing itself, or a post-mitigation retest. None of those are large, but they’re real, and I’d rather name them than let you find them later.

Radon also isn’t the same job as sealing your house for comfort and energy, even though the two overlap. Air sealing and a proper water-resistive barrier are their own scope, and I covered those in which energy efficient features are worth paying for. A tight house with no radon path is great. A tight house sitting on unvented soil gas without a pipe is tighter around the wrong thing.

And if your build is rural, radon sits alongside the other below-grade decisions that get made early, like well and septic and the site prep work covered in how to prepare land to build a house. These all land in the same window of the schedule, which is why they belong in design rather than in a panic during excavation.

What I do on every house I build

I rough in a passive radon system on every home, in every county listed in that table, without waiting to be asked. It gets drawn into the plans during the design phase, priced into the construction contract, and installed at the foundation stage. Then I tell the owner to test the first winter they’re in the house, and what to do with the result.

I’m involved in every phase of every build, which in practice means I’m the one making sure the gravel is clean, the poly is actually lapped and sealed rather than thrown down, and the pipe is labeled so a future electrician doesn’t cut into it wondering what it is. A radon system that was installed carelessly is a pipe, not a system, and you won’t find out which one you got until you test.

The reason this is a design-phase item and not a field decision is simple: the pipe needs a chase to run in, and chases are a plan question. We handle plan development and design and engineering in house, so the radon pipe gets a home in the drawings before framing starts instead of being shoehorned into whatever wall is closest. You don’t need to go hire that out. What that phase looks like and what gets locked in it is in the design phase explained, and design is covered by a fixed design fee, quoted per project.

If you’re planning a build in Teton Valley or anywhere in eastern Idaho and you want to know how involved you’ll need to be in decisions like this one, here’s what that actually looks like. Radon is one of maybe forty of these decisions, and handling them so you don’t have to is the job.

Building science items like this rarely make the highlight reel, and they’re the ones that quietly separate a house that performs from one that just looks finished. Same category as wildfire resistant construction and what radiant floor heat really costs, both of which get decided in the same early window.

Want the radon rough-in and the rest of the below-grade decisions handled on your build? Get in touch or call (208) 520-0636 and we’ll walk through your lot and your plans.

Frequently asked questions

Can you test for radon before the house is built?
Not usefully. Radon is measured inside a finished, closed-up building, so a reading on a vacant lot doesn’t predict your house. Soil gas testing exists but isn’t reliable enough to base a decision on. That uncertainty is the argument for roughing in a passive system rather than waiting.

Does a radon system in a new home need a fan?
Not necessarily. A passive rough-in uses stack effect to vent soil gas with no fan, and sometimes that’s enough to stay under 4.0 pCi/L. You test after moving in, and if the number is at or above the action level, a fan goes on the existing pipe in the attic. The rough-in is what makes that easy.

How much does radon mitigation cost in Idaho?
The Idaho Department of Health and Welfare publishes $300 to $500 for radon-resistant features installed during construction, $1,500 to $3,500 for a professional retrofit on an existing home, and $300 to $600 for a DIY kit. Those are agency figures, not a builder’s quote, and the construction-stage option is the cheapest by a wide margin.

Is radon worse in a basement than on a slab?
Basements often test higher because they’re below grade with more soil contact and stronger stack effect. That doesn’t make a slab house safe. Slab-on-grade homes test above the action level regularly in Zone 1 counties, so both get the same rough-in on my builds.

Do I have to disclose radon when I sell an Idaho home?
If you have test results, buyers and their inspectors will ask, and radon testing is common during Idaho home inspections. A documented passive system with a test showing you’re under the action level is an asset in that conversation. No result at all just means the buyer runs their own test and you find out on their timeline.