TL;DR: A mudroom in an Idaho house gets sized by bench bays, not square feet. Figure 12 to 16 inches of wall per person, 36 inches of clear floor in front of the bench, and a path that runs garage, mudroom, kitchen without crossing a living space. Hooks at 48 inches for kids and 60 to 66 for adults. Bench seat 17 to 18 inches high, 16 to 18 deep.
Hanging closets want 24 inches of depth, which is the same number the National Electrical Code uses when it defines closet storage space. Pantry shelves want 14 inches and never more than 16. The laundry is limited by one thing most owners never hear about: how far the dryer can push air. Below is how I lay the whole storage program out, and which parts of it the state of Idaho actually inspects.
Contents
- How big should a mudroom be?
- Where does the mudroom actually go in the floor plan?
- What goes in the mudroom, and at what heights?
- How deep does a closet have to be?
- Why can’t I put the light fixture I like in my closet?
- Can the electrical panel go in my mudroom or a closet?
- How deep should pantry shelves be?
- Where can the laundry room go, and what limits it?
- What does Idaho’s building code actually cover here, and what does it not?
- How do you store ski and snow gear without the house smelling like a locker room?
- When are mudroom and storage decisions due on my build?
- What does this cost, and what is not included?
- Who handles the mudroom and storage design on your build?
- Frequently asked questions
How big should a mudroom be?
A mudroom should be sized off the number of people who come through it, not off a square footage number somebody read in a magazine. The working unit is the bay: one person’s bench seat, hooks above it, a cubby below it and a shelf over the top. Give each bay 12 to 16 inches of wall width, and give the room 36 inches of clear floor in front of the bench so somebody can sit down and pull a boot off without blocking the door.
That math lands most Teton Valley houses in the same place. Here is what I build to.
| Household | Bench bays | Bench wall length | Room depth I want | What usually gets added |
|---|---|---|---|---|
| Couple, no kids, second home | 2 | 3 to 4 ft | 6 ft | Ski and boot wall instead of a third bay |
| Couple plus two kids | 4 | 5 to 6 ft | 7 ft | Closed upper doors so the mess does not show |
| Family of five or six | 5 to 6 | 7 to 8 ft | 8 ft | A second bench run on the opposite wall |
| Full-time house, dogs, ski family | 6 plus | 8 to 10 ft | 9 to 10 ft | Dog wash, drying closet, floor drain |
Note what the table does not say. It does not say 8 by 10. A mudroom that is 8 by 10 and shaped wrong is worse than one that is 6 by 9 and shaped right, because the thing that makes a mudroom work is the length of the bench wall and the width of the walk-through, not the area. I would rather give you a long, shallow mudroom than a square one every time.
And here is the part nobody tells you: the mudroom is the room owners regret shrinking more than any other room in the house. When a budget conversation gets tight during design, the mudroom is the first place people cut, because it is not a room guests see. Three winters later it is the room they are mad about. If something has to give, take the square footage out of a guest bedroom.
Where does the mudroom actually go in the floor plan?
On the path you use, not the path guests use. In a Teton Valley house that means the garage, because almost nobody in this valley walks in the front door. The sequence I want is garage, mudroom, then kitchen or pantry, in that order, with no detour through a living space.
Three placement rules I hold to:
- The mudroom goes between the garage and the kitchen, not off the hallway. Groceries and gear both arrive from the garage. If the mudroom is off a hall and the kitchen is on the other side of the house, you will carry wet bags across finished floor for thirty years.
- Do not make the mudroom the only path to the laundry. If every load of laundry has to walk through the boot pile, both rooms get worse. Adjacent is good. Shared is a compromise. Stacked on top of each other is usually a mistake.
- Keep the mudroom off the exterior corner if you can. A mudroom buried on an inside corner of the plan has two fewer cold walls, and on a house where the garage wall is already a thermal break, that matters. See how we insulate and air seal the garage-to-house wall for why that assembly gets special treatment.
One more thing about placement in snow country. If the mudroom shares a wall with the garage, and the garage is held at 45 to 55 degrees for frost protection the way most of ours are, that wall still has to be built as an envelope wall. Idaho’s energy code is explicit that a garage heated for frost protection or intermittent use is not conditioned space, so the mudroom side of that wall is where your insulation and air barrier live. I wrote the whole argument out in the post on heating a garage in Idaho.
What goes in the mudroom, and at what heights?
This is the part that gets decided badly, because it usually gets decided from a drawing instead of from the people who will use it. Heights are not a style choice. A hook set at the wrong height is a coat on the floor.
| Element | Dimension I build to | Why |
|---|---|---|
| Bench seat height | 17 to 18 in | Same as a dining chair. Lower and adults struggle to stand up with a boot in hand. |
| Bench seat depth | 16 to 18 in | Deep enough to sit square. Deeper and the back of the bench becomes a junk shelf. |
| Hook height, kids | 48 in | A seven-year-old can reach it. A four-year-old needs 40. |
| Hook height, adults | 60 to 66 in | Coat hangs clear of the bench seat instead of sitting on it. |
| Upper shelf | 66 to 72 in | Helmets, hats, bins. Above the adult hooks, below the ceiling clutter zone. |
| Open boot cubby | 12 to 14 in high, 16 in deep | A size 12 pac boot is about 13 inches tall and 13 deep. Measure yours. |
| Bay width | 12 to 16 in | 16 for adults in ski shells. 12 works for kids. |
| Clear floor in front | 36 in minimum | One person seated, one person walking past, at the same time. |
Two details that earn their keep. First, put a receptacle at bench height, not just at the appliance wall, because every family ends up charging something in the mudroom and the alternative is a cord across the floor. Second, put solid blocking behind every bench, hook rail and shelf before the drywall goes on. Anything that will later be screwed to the wall needs wood behind it, and after the rock is up it is a change order. That is one of the items on my pre-drywall walkthrough list, and it is the cheapest insurance in the whole build.
On material: a mudroom bench sits in standing snowmelt six months a year. Do not let anyone put MDF there. MDF takes paint beautifully and turns to oatmeal when it gets wet. Poplar at the bench and the base, and a real wood species anywhere you want stain grade. I go into the species-by-species version of that in the post on interior doors and trim.
How deep does a closet have to be?
Twenty-four inches, and you do not have to take my word for it, because the electrical code already settled the number. When the National Electrical Code needs to define the volume of a clothes closet so it can keep light fixtures out of it, Section 410.16(A) describes the clothes closet storage space as the volume bounded by the sides and back closet walls and by planes “parallel to the walls at a horizontal distance of 600 mm (24 in.) from the sides and back of the closet walls,” running from the floor up to 6 feet or to the highest clothes-hanging rod, whichever is higher.
That is the code, written by electricians, independently arriving at the same 24 inches a cabinet shop would tell you. A shirt on a hanger is about 22 inches wide at the shoulder. Twenty-four inches of closet depth clears it with room for the door to close. Anything shallower and the clothes press against the back wall; anything deeper is floor area you paid for and cannot reach.
| Closet element | Dimension | Note |
|---|---|---|
| Hanging depth | 24 in | Matches the NEC 410.16(A) storage-space definition. |
| Reach-in closet depth | 24 to 26 in finished | 26 if you want a door jamb and a shelf cleat without crowding. |
| Walk-in, hanging one side | 24 in hang plus 36 in walkway = 60 in interior width | 48 in works and feels tight with a drawer bank. |
| Walk-in, hanging both sides | 24 + 36 + 24 = 84 in interior width | 7 feet. Below that, two people cannot pass. |
| Double-hang rods | Lower 40 to 42 in, upper 80 to 84 in | Doubles capacity for shirts and folded pants. |
| Single long-hang rod | 66 to 70 in | Dresses, coats, ski shells. |
| Shelf above the rod | 12 to 14 in deep | The code treats the shelf width as part of the storage volume. |
One subtlety worth knowing because it changes a primary closet layout. NEC 410.16(A) adds that for a closet that permits access to both sides of a hanging rod, the storage space also includes the volume below the highest rod extending 12 inches on either side of the rod, along the entire length of the rod. In plain English: an island rod you can walk around counts as storage space on both faces, and that is the geometry a light fixture has to stay clear of.
Why can’t I put the light fixture I like in my closet?
Because the code has opinions about closets and fire. NEC 410.16(C) is blunt about it: “Incandescent luminaires with open or partially enclosed lamps and pendant luminaires or lamp holders shall not be permitted.” That rules out the bare-bulb keyless fixture, and it rules out the small pendant that looks great in the photo of somebody’s primary closet.
What is permitted under 410.16(B) is surface-mounted or recessed incandescent or LED luminaires with completely enclosed light sources, surface-mounted or recessed fluorescent luminaires, and surface-mounted fluorescent or LED luminaires specifically identified as suitable for installation within the storage space itself.
And then 410.16(D) sets how far the fixture has to stay from that 24-inch storage volume:
- 12 inches for a surface-mounted incandescent or LED fixture with a completely enclosed light source, on the wall above the door or on the ceiling.
- 6 inches for a surface-mounted fluorescent fixture, same locations.
- 6 inches for a recessed incandescent or LED fixture with a completely enclosed source, in the wall or ceiling.
- 6 inches for a recessed fluorescent fixture, in the wall or ceiling.
Put those two things together and you get a design constraint, not a trivia question. In a reach-in closet that is 24 inches deep, the storage volume is the whole closet. A surface-mounted enclosed LED needs 12 inches of clearance from it, which is why that fixture ends up on the ceiling outside the closet line or on the wall above the door. There is an exception: a surface-mounted fluorescent or LED fixture may sit inside the storage space where it is identified for that use. That is the listed LED strip, and on a walk-in it is usually the right answer anyway, because a strip under the shelf lights the clothes instead of the top of your head.
Can the electrical panel go in my mudroom or a closet?
Mudroom yes. Clothes closet no. NEC 240.24(D) keeps overcurrent devices out of the vicinity of easily ignitible material, and the code names clothes closets as the example. A panel surrounded by hanging fabric is exactly the condition that rule exists to prevent.
This comes up more than you would think, because a panel has to go somewhere and a designer looking at a plan sees a closet as free wall. It is not free wall. What works instead, and what I spec on most builds, is the mudroom, the garage wall or a dedicated utility space, with the working clearance in front of it kept clear of shelving and bins for the life of the house. If you want the sizing side of that conversation, including what an EV charger adds, read what size electrical panel a new Idaho house needs.
While we are here: a utility sink in the mudroom changes the electrical rules around it. Idaho adopted the 2023 National Electrical Code and then rewrote the ground-fault rules fairly heavily, including deleting the laundry-area requirement outright. But amendment (e) replaced NEC 210.8(A)(8) with ground-fault protection for “Sinks – located in areas other than kitchens where receptacles are installed within one and eight tenths (1.8) meters (six (6) feet) of the inside edge of the sink.” So the sink pulls the requirement back in even where the laundry-area rule went away. I laid out the full Idaho amendment table in the pre-drywall walkthrough post rather than repeat it here.
How deep should pantry shelves be?
Fourteen inches, and never more than 16. This is the single most common storage mistake in a custom house, and it is always made with good intentions.
An 18 or 24 inch pantry shelf looks generous on a plan and holds twice the cans. What it actually does is create a back row you cannot see. Cans go in the back row, get forgotten, and two years later you are throwing out expired food you paid for. A 14-inch shelf holds one row of everything and you can read every label from the aisle. The capacity you lose in depth you get back by adding shelves, because a 14-inch shelf can be spaced closer vertically without becoming a cave.
- Shelf depth: 14 in for dry goods, 16 in maximum for appliances and bulk.
- Shelf spacing: 14 to 16 in for tall items, 10 to 12 in for cans and jars. Make at least half of them adjustable.
- Bottom shelf: keep it 6 to 8 in off the floor so a mop reaches under, or make it a drawer base.
- Walk-in pantry: 5 by 7 feet is the honest minimum with shelving on two walls and a 36-inch aisle. Below that build a wall of cabinets instead and spend the money on depth of drawers.
- Counter in the pantry: if you can give it 24 inches of counter and a receptacle, the coffee maker and the mixer leave the kitchen and never come back. This is the highest-value 4 square feet in the house.
On a two-level house, remember the pantry door swing and the pantry light both have to be resolved before framing, because a pocket door needs a clear wall cavity with no wiring, plumbing or blocking in it. That decision belongs in the door schedule, which is covered in the interior doors and trim post.
Where can the laundry room go, and what limits it?
The dryer limits it. Not the plumbing, not the floor framing, not the square footage. How far the dryer can push wet air through a duct is what decides whether the laundry can sit where you want it, and almost no owner hears this during design.
The residential code’s specified-length method caps the exhaust duct at 35 feet from the connection at the dryer’s transition duct to the outlet terminal, and every fitting in that run eats into the 35 feet:
| Fitting | Counts as this much duct |
|---|---|
| 4 in radius mitered 45 degree elbow | 2 ft 6 in |
| 4 in radius mitered 90 degree elbow | 5 ft |
| 6 in radius smooth 45 degree elbow | 1 ft |
| 6 in radius smooth 90 degree elbow | 1 ft 9 in |
| 8 in radius smooth 45 degree elbow | 1 ft |
| 8 in radius smooth 90 degree elbow | 1 ft 7 in |
| 10 in radius smooth 45 degree elbow | 9 in |
| 10 in radius smooth 90 degree elbow | 1 ft 6 in |
Read that table twice. A laundry buried in the middle of a floor plan with four tight mitered 90s to get out to a wall has already spent 20 of its 35 feet before a single straight run. Specify long-radius smooth elbows instead of mitered ones and the same four turns cost about 7 feet. That one substitution is often the difference between a laundry where you want it and a laundry where the duct allows it.
The rest of the rules that matter on a real build: the duct is smooth-interior rigid metal not less than 0.0157 inch thick, which is No. 28 gage. Joints get mechanically fastened and no screw may protrude more than 1/8 inch into the duct, because every protruding screw is a lint hook. The flexible transition duct from the dryer to the rigid duct must be a single listed length not longer than 8 feet, and it is never concealed in construction. The duct terminates outside with a backdraft damper, and screens are not installed at the termination. A screen at a dryer vent is a lint trap on the outside of your house.
Two more constraints on where a laundry can go. The first is ceiling height, and it works in your favor. A laundry room is one of the few spaces the residential code lets you build lower than 7 feet. R305.1 requires habitable space and hallways to have a ceiling height of not less than 7 feet, while bathrooms, toilet rooms and laundry rooms are allowed not less than 6 feet 8 inches. The City of Boise prints the same figures on its R305 handout. That exception is how a laundry fits under a stair landing when nothing else will.
The second is plumbing. The washer box, standpipe and trap in Idaho are built to the Idaho State Plumbing Code, which is the 2015 Uniform Plumbing Code with state amendments, not the plumbing chapters of the residential code. Your plumber knows this. Your floor plan should respect it.
If the laundry is upstairs, put it in a pan with a drain, and put the drain somewhere a failure can go. That is not code. That is twenty years of watching supply lines fail at two in the morning.
What does Idaho’s building code actually cover here, and what does it not?
This is the part of the run that surprised me, and it changes how you should think about everything above.
Idaho’s building code rules adopt the 2018 International Residential Code, but not all of it. IDAPA 24.39.30, Section 600.03 adopts “Parts I, II, III, and IX of the 2018 Edition for one (1)- and two (2)- family dwellings, with the following amendments.” Parts I, II, III and IX are administration, definitions, building planning and construction, and referenced standards. Part V, the mechanical chapters, is not on that list. Neither are the plumbing or electrical parts, and those have their own homes: plumbing at IDAPA 24.39.20, which adopts the 2015 Uniform Plumbing Code as the Idaho State Plumbing Code, and electrical at IDAPA 24.39.10, which adopts the 2023 National Electrical Code with a long list of Idaho amendments.
So the 35-foot dryer duct limit I just walked you through is in Chapter 15, which sits in Part V. It is not in the part of the residential code that Idaho’s building code rules adopt statewide. Where does it bind? Two places. The appliance manufacturer’s installation instructions, which are enforceable as part of the appliance listing, state a maximum equivalent duct length that is usually in the same range and sometimes shorter. And whatever mechanical provisions your local jurisdiction has adopted on its own, which in Teton, Jefferson, Bonneville and Madison counties is a question to ask at permit, not a question to assume.
There is one interesting exception that proves the point. Idaho’s own amendment (h) to the residential code deletes Section R303.4 and replaces it with a requirement that dwelling units be provided with whole-house mechanical ventilation in accordance with Section M1505.4. M1505.4 is in Part V. Idaho reached into the mechanical part it did not adopt and pulled one section back in by reference, which tells you the omission of the rest was deliberate. If you want the ventilation side of that, I wrote it up in the whole-house ventilation post.
| What governs it in Idaho | Which rule | What it covers in your mudroom and laundry |
|---|---|---|
| 2018 IRC, Parts I, II, III, IX | IDAPA 24.39.30 Sec. 600.03 | Ceiling height, garage separation, fire blocking, structure, egress |
| 2015 Uniform Plumbing Code, amended | IDAPA 24.39.20 Sec. 600 | Washer box, standpipe, trap, utility sink, drains |
| 2023 National Electrical Code, amended | IDAPA 24.39.10 Sec. 600.01 | Receptacles, closet light clearances, panel location, ground fault |
| Manufacturer instructions and local adoption | Appliance listing plus county | Dryer duct length, makeup air, appliance clearances |
None of this is a reason to build it loose. It is a reason to put the numbers in the drawings rather than hoping an inspector catches them. An inspection is a floor, not a standard. That is the same point I make in the post on what inspections happen when you build.
How do you store ski and snow gear without the house smelling like a locker room?
You give the wet stuff a place to dry with air moving across it and a floor that can get wet. Every mudroom failure I have been called back to in this valley is the same failure: gear went into a closed cabinet wet and stayed wet.
What works, in the order I would spend the money:
- Open storage for anything wet. Hooks and open cubbies for shells, gloves and boots. Closed doors are for the things that are already dry. If you want doors for the look, make them louvered or leave the bottom open.
- A hard floor with a drain, if the mudroom sits on slab. Tile over a slab with a floor drain is the single best mudroom floor in snow country, and it is nearly free to add while the slab is being formed and impossible to add later. Your foundation type decides whether this is even on the table, which is one more reason to settle basement, crawl space or slab early.
- Heat in the floor. A mudroom is the highest-value radiant zone in the house per square foot, because it is the one room where the floor is doing work: it dries the boots. Radiant floor heat in a 60 square foot mudroom costs very little next to the rest of a system and you feel it every single day.
- A drying closet with air actually moving through it. A small closet with a boot dryer, a hanging bar and a dedicated exhaust fan on a timer, or a transfer grille to a return. Without air movement it is a wet box.
- A dog wash, if you have dogs. Thirty inches wide, a hand shower on a hose, a curb, and a tile surround that goes up high enough to survive a shaking dog. Plumb it while the walls are open.
A note on the stuff that will not fit indoors no matter how well you plan: skis, bikes, sleds and the rooftop box. That belongs in the garage on a wall system, not in the mudroom, and the garage wall you hang it on needs blocking too. People spec garage storage last and then discover every wall is either door, window or panel.
When are mudroom and storage decisions due on my build?
Earlier than almost anyone expects, because storage is framing, not finish. The bench looks like a finish item. The wall it attaches to, the blocking behind it, the duct behind that wall and the receptacle at bench height are all framing-stage decisions.
| Decision | Due by | What it locks | Cost of changing it later |
|---|---|---|---|
| Mudroom location and size | Schematic design | The whole garage-to-kitchen path | A redraw and, past permit, a resubmittal |
| Floor drain and slab slope | Before the slab is formed | Whether a wet mudroom floor is possible | Effectively impossible after the pour |
| Laundry location and dryer duct route | Before framing | Where the laundry can legally and practically go | Reframing, or a relocated laundry |
| Radiant zones | Before the slab or topping pour | Mudroom floor heat | Not retrofittable in that floor |
| Blocking for benches, shelves, hooks | Before drywall | What can be screwed to a wall for 30 years | Change order, open the wall |
| Closet rod and shelf layout | Before drywall for lighting, before cabinets for the rest | Light fixture clearances under NEC 410.16 | Moving a fixture and patching |
| Millwork species, finish, door style | With the rest of the selections | Shop schedule and lead time | Delay, because the shop has already started |
These dates do not float. They sit inside the broader selections calendar, which I walk every client through in the post on when finish selections are due, and they are part of the reason a 14 to 18 month build stays on schedule or does not.
What does this cost, and what is not included?
I am not going to publish a per-square-foot number for a mudroom, because it would be useless to you. Storage millwork is the most variable line in a house. Two mudrooms the same size, one in paint-grade poplar with open cubbies and one in stain-grade walnut with inset doors and integrated lighting, are not the same scope and are not within sight of each other on price.
Here is what I will tell you. SwagerBuilds custom homes start at $400 per square foot of conditioned space and go up on the Teton Valley and Eastern Idaho side, and start at $1,000 per square foot and go up in Jackson Hole. That is construction cost on conditioned square footage, fixed price after design lock. Site work, permits, landscape and furnishings land on top of it. The full version of that math, with one worked example, is in the honest cost to build in Teton Valley.
What a storage or millwork allowance in somebody’s bid usually does not include, and what you should ask about by name:
- Blocking and any framing changes to carry the bench, shelving or a wall-hung system
- The receptacles and lighting inside the closets, pantry and mudroom
- Closet shelving systems, which fall between the cabinet bid and the trim bid and get missed by both
- Floor drain, slab slope and the tile curb at a dog wash
- Radiant tubing or an electric mat in the mudroom floor
- Door hardware for closet and pantry doors, which is a separate line from the doors
- The drying closet’s exhaust fan, its duct and its control
Vague allowances are how custom home budgets fall apart, and storage is the category where it happens most, because nobody can picture what a millwork allowance bought until it shows up. How construction allowances work and why builders set them low is worth ten minutes before you sign anything.
Design is sold as the design agreement, at a fixed design fee, quoted per project. No numbers on a custom project come out before that is signed, because an honest number requires a drawn plan.
Who handles the mudroom and storage design on your build?
We do, start to finish, and that is deliberate. The mudroom is exactly the kind of room that falls through the cracks when a homeowner is holding a separate architect, a separate interior designer and a separate cabinet shop together by themselves. The bench is a cabinet decision, the blocking is a framing decision, the floor drain is a concrete decision and the closet light is an electrical decision, and all four have to agree.
On a SwagerBuilds project the design agreement is where the storage program gets locked: how many bays, where the laundry sits, what the pantry holds, whether there is a dog wash. Plan development and the drawing set are coordinated in-house, so a change to the mudroom wall comes back revised the same week rather than waiting on an outside firm’s calendar. Engineering coordination runs through people I have worked with for twenty years.
Interior selections, including the millwork species and the door style, get sequenced so they do not blow the schedule. And the cabinetry and millwork are milled in our own shop in Rigby, in alder and walnut, which is why a locker bay can be built to a 14-inch module instead of whatever a catalog offers.
I am involved in every phase of every build, and there are 24/7 cameras on every job, so if you want to see the blocking go in behind your bench, you can watch it happen. What the design phase actually produces and the nine stages of a build both go deeper on how that works.
Built different. Built right. Built by SwagerBuilds.
Frequently asked questions
How big should a mudroom be in an Idaho house?
Size it by bench bays, not square feet. Allow 12 to 16 inches of wall width per person, plus 36 inches of clear floor in front of the bench. A couple needs about 3 to 4 feet of bench wall, a family of four about 5 to 6 feet, and a full-time ski family with dogs 8 to 10 feet plus a drying closet and a floor drain. Room depth of 7 to 9 feet covers most Teton Valley houses. A long, shallow mudroom beats a square one of the same area every time.
How deep does a clothes closet need to be?
Twenty-four inches of hanging depth. A shirt on a hanger is about 22 inches across the shoulders, and the National Electrical Code uses the same 24 inches when Section 410.16(A) defines clothes closet storage space as the volume extending 24 inches from the sides and back walls. A walk-in with hanging on one side wants about 60 inches of interior width, and 84 inches if you hang both sides, so two people can pass.
Can I put a light fixture or the electrical panel in my closet?
A fixture yes, with limits. A bare or partially enclosed incandescent lamp and any pendant or lampholder are not permitted in a clothes closet under NEC 410.16(C). Enclosed LED and fluorescent fixtures are, and 410.16(D) requires 12 inches of clearance from the storage space for a surface-mounted enclosed LED and 6 inches for recessed and surface fluorescent types, unless the fixture is specifically identified for installation inside the storage space. The electrical panel is a flat no: NEC 240.24(D) keeps overcurrent devices out of clothes closets. Put it in the mudroom, the garage or a utility space.
How far can my laundry room be from an outside wall?
The dryer duct decides. The specified-length method in the residential code caps the exhaust duct at 35 feet from the dryer’s transition duct to the outlet, and fittings count against it: a 4-inch mitered 90-degree elbow counts as 5 feet, while a long-radius smooth 90 counts as little as 1 foot 6 inches. Four cheap elbows spend 20 of your 35 feet. Note that Idaho’s building code rules adopt only Parts I, II, III and IX of the 2018 residential code, so the mechanical chapter is not state-adopted; the limit binds through the appliance manufacturer’s instructions and whatever your county adopted. Design to it either way.
Can a laundry room have a lower ceiling than the rest of the house?
Yes. IRC Section R305.1 requires habitable space and hallways to have a ceiling height of not less than 7 feet, but allows bathrooms, toilet rooms and laundry rooms a minimum of 6 feet 8 inches. That exception is how a laundry fits under a stair landing or in a lowered bay when nothing else will. The plumbing in it still follows the Idaho State Plumbing Code, which is the 2015 Uniform Plumbing Code with state amendments.
Get a real number on your build
If you are planning a custom home in Teton Valley, Driggs, Victor, Tetonia, Eastern Idaho or Jackson Hole and you want the storage program designed into it instead of bolted on at the end, call me at (208) 520-0636. Bring your plan if you have one and the number of boots that come through the door. I will tell you straight whether the mudroom you have drawn will work in February.