What a Custom Home Costs in Idaho Falls & Bonneville County (2026)

I’m Bryce Swager. I’ve been building custom homes in eastern Idaho for 20 years, and I grew up in a family that’s been building businesses here for four generations — I’m the first generation to build homes. This page is a straight look at what a custom home actually costs in Bonneville County in 2026 — construction costs, permit fees, plan review, inspections, and the surprises that hit owners mid-build.

No allowance games. Real construction costs, cited fee schedules, and the timeline you should plan around. If you want to talk through your specific project, call me at (208) 520-0636.

The 2026 Pricing Frame

SwagerBuilds custom homes in Bonneville County run $400 per square foot and up in 2026 construction cost, on interior living space. How far up it goes depends on the finishes and fixtures you choose, and that’s your call to make. Once the design and selections are set, your price is fixed. A fixed project price is locked only after a signed design agreement. What moves your number within that range:

• Finish level. Production-grade cabinetry and tile versus custom millwork out of my Rigby shop is the biggest single lever on your number.
• Site complexity. City sewer and water on a flat lot is a different number than acreage with a well, septic, engineered driveway, and long utility runs.
• Structural spans and design. Open spans, vaulted ceilings, walkouts, and heavy timber carry engineering and framing cost a simple rectangle doesn’t.

All-in project cost (land improvements, soft costs, design fee, contingency, financing carry) typically adds another 35–50% on top of construction cost. Where a Bonneville County custom lands above the entry point depends on lot, finish level, and how much site work the parcel demands. Unincorporated sites with well + septic and long utility runs push it up from there. Serviced Idaho Falls and Ammon lots with straightforward plans sit closest to the entry point.

National context: NAHB’s 2024 Cost of Constructing a Home study puts the average single-family construction cost at record levels, with construction accounting for 64.4% of the total new-home price. Their per-square-foot average is roughly $162/SF on the construction cost side — which strips out lot, financing, marketing, and profit. Eastern Idaho custom homes with high-efficiency envelopes, snow-load engineering, and specified (not allowance) finishes run 2.5–6x that baseline depending on scope and finish. Eastern Idaho isn’t cheap anymore; it’s a normal Mountain West market with normal Mountain West costs.

Permit Fees in Bonneville County

Here’s the first honest thing to know: Bonneville County itself does not publish an inline residential permit fee table. The county’s Building Permit & Zoning Fees page routes visitors to downloadable Public Works, Subdivision, and Building fee PDFs, and the residential building permit fee schedule isn’t posted as inline HTML. You get a project-specific fee estimate by calling Planning & Building at 208-529-1350 or Building Inspection at 208-524-7920.

For a Bonneville County resident, whether your permit fee comes from the county or from a city depends on where the lot is. Inside Idaho Falls or Ammon city limits, city fees apply. Outside city limits, the county issues the permit. The city fee schedules are the practical proxy for what most Bonneville County residents pay, because most of the population lives inside Idaho Falls or Ammon.

Idaho Falls Permit Fees

The City of Idaho Falls publishes its current fee schedule as a PDF: the Idaho Falls 2025–2026 Fee Schedule. Building fees are calculated off construction valuation (ICC valuation tables applied to your square footage and construction type), and the plan check fee is typically 65% of the permit valuation for residential construction. Work started without a permit triggers a double-fee assessment. Their Permit Processing page hosts the full submittal checklist and process flow.

Building Division contact: 308 Constitution Way, 208-612-8100. Submit through the city’s Community Development portal.

Ammon Permit Fees

Ammon’s Building Permits page lists review time explicitly at “5–10 business days” and routes all submissions through the BluePrince portal. Current fees are set by Fee Resolution Amendment 2025-002 (Spring 2025). Building Department at 2135 South Ammon Road, 208-612-4000, open Mon–Fri 9–5.

What You Actually Pay

On a typical custom home in Bonneville County in 2026, permit-side hard costs generally land in this range:

Line Item	Typical Range
Building permit fee (ICC valuation × fee schedule)	$3,500 – $6,500
Plan check fee (approx. 65% of permit fee in Idaho Falls)	$2,275 – $4,225
Mechanical permit	$400 – $800
Plumbing permit	$400 – $800
Electrical permit (state)	$300 – $700
Water/sewer connection or well/septic permits	$1,500 – $9,000+
Impact fees (varies by jurisdiction and district)	$0 – $6,000+

Rough total permit-side: $8,000 to $28,000 depending on jurisdiction, whether you’re on city services or well/septic, and how impact fees stack. Confirm exact numbers against the current PDFs linked above before you sign a contract.

Site Work, Setbacks, and Snow Load

Two design constraints hit almost every Bonneville County custom home:

Setbacks. For most single-family residential zones in Bonneville County and adjoining Idaho Falls, the typical standard is a 20-foot front setback from any public street, side yards of 8 inches per foot of building height (minimum 7’6″), and a 25-foot rear yard on interior and corner lots. Verify against the current Bonneville County code or Idaho Falls Title 11 Chapter 3 before you finalize a site plan.

Snow load. This is a big one owners miss. The ASCE 7 ground snow load lookup for Bonneville County returns “Site Specific Location: Case Study Required” — meaning there’s no single county-wide pg value you can plug into a truss calc. Your engineer has to establish a design ground snow load from a site-specific analysis or the University of Idaho 2015 Ground Snow Loads reference. That case study drives truss depth, sheathing, and load path — and it drives cost. Skip it and you’ll get bounced at plan review.

What Actually Drives Cost Per Square Foot

NAHB’s 2024 breakdown gives the cleanest apples-to-apples view of where money goes on a custom build. Per their 2024 Cost of Constructing a Home data:

• Interior finishes: 24.1% of construction cost
• Major system rough-ins (HVAC, plumbing, electrical): 19.2%
• Framing: 16.6%
• Exterior finishes: 13.4%
• Foundations: 10.5%
• Site work: 7.6%
• Final steps (cleanup, driveway, landscape): 6.5%
• Other: 2.1%

Foundations are 11% of construction cost on the NAHB survey — the item you cannot cheaply fix later. On our Bonneville County builds we bid foundations and flatwork through a dedicated concrete contractor that specs air-entrained mixes for our freeze-thaw cycles, so the number goes into the fixed price at real cost, not an allowance.

Notice: interior finishes are the single biggest bucket. That’s cabinets, countertops, tile, flooring, paint, trim, lighting, plumbing fixtures, appliances. It’s also the bucket cost-plus builders bury inside allowances. If your contract has a $65,000 “cabinet allowance” for a house with 42 linear feet of upper cabinets, you’re going to blow through it, and you won’t know until you go select. Get finish selections priced before you sign — the design agreement phase is exactly when this happens.

Timeline

For a typical Bonneville County custom home in 2026, plan on:

• Design + engineering (design agreement phase): 12–16 weeks
• Plan review + permit issuance: 1–4 weeks in Idaho Falls; 5–10 business days in Ammon; project-specific in unincorporated county
• Foundation and framing: 3–5 months
• MEP, insulation, drywall: 2–3 months
• Finishes and closeout: 3–4 months

Total: roughly 9–13 months from signed construction contract to closeout for a straightforward serviced-lot build. Add 1–3 months for unincorporated sites with well and septic, or for owners still making finish decisions after framing starts.

Common Cost Surprises

These are the line items that most often blow up a first-time custom home budget in Bonneville County:

• Snow load engineering. Case-study analysis and heavier trusses on top of a standard package.
• Impact and connection fees. Water, sewer, and district impact fees stack fast on the same permit.
• Well and septic on unincorporated sites. $12,000 to $35,000+ depending on depth, drain field size, and Eastern Idaho Public Health requirements.
• Driveway on longer parcels. Every 100 feet of gravel drive adds real money; asphalt or concrete much more.
• Rock and clay soils. Discovered during excavation, not at bid. A soils report before signing is cheap insurance.
• Finish creep. The single largest driver of owner-side overruns. Every finish upgrade you decide on after framing costs 2–4x what it would have cost at spec — which is why we spec every finish in the design agreement, not in a construction allowance.
• Utility runs on rural lots. Power drops, propane, fiber — check with the utility before you close on the land.

None of those are hidden if you have a builder pricing the actual house, not a stock template. They’re only hidden when the contract runs on allowances.

Fixed-Price After Design Agreement vs. Cost-Plus in Bonneville County

Most custom home contracts in this market are cost-plus with allowances. That’s the honest truth. The reason it’s popular with builders is straightforward: the builder doesn’t have to do detailed spec pricing before signing. The reason it’s expensive for owners is the same reason — nobody actually knows what the house costs when you sign the contract.

SwagerBuilds writes fixed-price construction contracts — but only after a signed design agreement. That means we spec every finish before construction pricing, get real bids from real subs on real materials, and take the risk that our numbers hold. It takes more work up front — the design agreement phase runs 12–16 weeks — but it’s the only contract structure where you actually know your number before you break ground. See custom home design services for how the design agreement phase works.

If a builder gives you a fixed-price bid that materially undercuts everyone else, look closely. Are the finish specs actually written in? Are cabinet quantities and door counts specified, or are they hidden in an “allowance”? A real fixed price is line-item defensible. A “fixed price” that isn’t line-item defensible is just an allowance contract with a friendlier label.

Financing and Draw Schedule

Most Bonneville County custom homes are built on a construction-to-permanent loan through one of the local banks or credit unions. Draws happen at defined project milestones — typically foundation, framing/dry-in, MEP rough-in, drywall, and final. Your bank will require a fixed contract price or a detailed cost-plus budget, along with lien waivers from every sub on every draw.

Interest on the construction loan is a real cost most owners underestimate. NAHB’s 2024 data pegs financing costs at 1.5% of sales price nationally — but that’s a builder-financing figure. On owner-financed construction, plan to carry the loan for the full construction period (9–13 months in Bonneville County), which meaningfully impacts your all-in cost.

How to Use These Numbers

Take your interior living space times the $400 per square foot entry point, then adjust upward for architecture, site, and the finishes you actually want. Add permits. Add lot cost if you don’t own yet. Add 8–12% for engineering, design agreement, and pre-construction. Add another 35–50% on top of construction cost for all-in project cost including land improvements, contingency, and financing carry. That’s a defensible planning number — not a quote.

For a more specific estimate, run my custom home cost calculator. For remodels or additions, use the kitchen/bath remodel calculator. To sanity-check my numbers against how I actually price jobs, read cost reality and the honest guide.

For more context on the broader region, see my eastern Idaho custom home builder page and the Idaho building permits by county pillar. If you’re specifically in Idaho Falls, Ammon, or Rigby, my city pages have finer-grained detail: Idaho Falls, Ammon, Rigby.

What clients say

SwagerBuilds holds a 5.0 rating across 9 Google reviews, all five-star. Three of them, verbatim:

They are very professional and personable. The crews were awesome and the owner was very involved. Biggest key point for me was always having great communication from the company every step of the way.

Hadley Bird — custom project, Google review

Quality work at a reasonable price. Used Swager twice and pleased both times with finished project. Definitely recommend.

Kenneth Deffendall — repeat client, Google review

Bryce did a complete gut and rebuild of our bathroom and it turned out awesome. The work was done in a timely manner and he was very professional. Would definitely hire again.

Josh Holverson — master bath remodel, Rigby ID, Google review

Read all 9 reviews →

Frequently Asked Questions About Custom Home Costs in Idaho Falls & Bonneville County

How much does it cost to build a custom home in Bonneville County in 2026?

SwagerBuilds custom home construction in Bonneville County starts at $400 per square foot of interior living space and goes up based on finishes, site, and design. A 2,500 square foot home at that entry point is about $1M in construction cost and roughly $1.35M all-in. All-in project cost typically adds 35 to 50 percent on top of construction cost.

Why do custom home quotes in Idaho Falls range from under $200 to over $400 per square foot?

Because builders measure on different bases. Some quote finished square footage including garages and unfinished space, some price a stock or semi-custom plan with allowances, and some quote construction only while others quote all-in. SwagerBuilds quotes construction cost on interior living space only, with finishes specified, and fixes the price after a signed design agreement. Before you compare numbers, ask every builder the same three questions: what square footage is counted, what is an allowance, and what is excluded.

How much are building permit fees in Idaho Falls and Bonneville County?

On a typical custom home, permit-side costs including the building permit, plan check, mechanical, plumbing, electrical, utility connections or well and septic permits, and impact fees usually land between about $8,000 and $28,000. The spread depends on whether the lot is in Idaho Falls, Ammon, or the unincorporated county, and whether it is on city services. Confirm against the current city or county fee schedule before you sign.

Does it cost more to build outside Idaho Falls city limits?

Often, yes. Unincorporated Bonneville County lots usually need a well and septic system, which commonly run $12,000 to $35,000 or more, plus longer driveways and utility runs. Serviced Idaho Falls and Ammon lots with straightforward plans sit closest to the entry point.

What does the $400 per square foot include?

Construction cost on interior living space, meaning finished, heated space. Unheated garages, covered outdoor space, and unfinished areas price separately, and land, design, and permits sit outside the construction number. The design agreement pins down scope and finishes before the construction price is fixed.

How long does a custom home take in Bonneville County?

Design and engineering take 12 to 16 weeks. Plan review runs 1 to 4 weeks in Idaho Falls and 5 to 10 business days in Ammon. Construction runs roughly 9 to 13 months on a serviced lot, plus 1 to 3 months for unincorporated sites with a well and septic.

Is fixed-price or cost-plus better for a Bonneville County custom home?

Fixed-price after a complete design is the only structure where you know your number before you break ground. Cost-plus with allowances is common in this market, but every allowance miss lands on the owner. If a fixed bid is far below the others, check whether finishes are actually specified or hidden in allowances.

Do Bonneville County homes need site-specific snow load engineering?

Yes. The ASCE ground snow load lookup flags Bonneville County as site specific, so there is no single county-wide design value. An engineer sets the snow load for your lot, and that drives truss and structural cost. Plans without it get bounced at review.

Start a Real Conversation About Your Number

The fastest way to turn a range into a real number is a 45-minute discovery call. Fill out the intake form or call me at (208) 520-0636.

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About the Author

Bryce Swager, Founder — 20-year Rigby custom home builder. BuildZoom score 94. Idaho Contractor Registration RCE-57499. Direct: (208) 520-0636. More about Bryce.

SwagerBuilds LLC · 4510 E 168 N, Rigby, ID 83442 · (208) 520-0636 · Idaho Contractor Registration RCE-57499