Small Barndominium Floor Plans in Washington State

A small barndominium, roughly 600 to 1,200 square feet of living space, is often the first building on a Washington acreage, a downsized retirement home, or a cabin on a parcel in the woods. Small plans are simple to frame, but the rules around them do not shrink with the floor area: the septic system has a minimum size, the permit still needs proof of water, and a vaulted open plan under a steel roof has to meet the same state energy code as a large house. On the wet side of the Cascades a small plan also has to find room for a place to shed rain gear; on the dry side, for a snow and dust lock.

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What actually changes with this feature

The look is the easy part. These are the decisions that follow from it.

Septic sizing has a floor

Washington's on-site sewage rule, WAC 246-272A-0230, sets the minimum design flow for a single-family residence at 120 gallons per bedroom per day, and never less than 240 gallons per day. A one-bedroom cabin is designed for the same 240 gallons as a two-bedroom house, and the local health jurisdiction can ask for more. A small plan saves on concrete and steel, not on the drainfield.

A vaulted open plan still meets the energy code

Washington's residential energy code, chapter 51-11R WAC, requires every new house to earn additional energy-efficiency credits on top of its insulation minimums. A dwelling under 1,500 square feet of conditioned floor area with less than 300 square feet of fenestration, the code's term for windows, skylights and glazed doors, is a small dwelling unit and needs 5.0 credits; cross either line and it needs 8.0. In a small vaulted plan, keeping the glass under 300 square feet is one of the cheapest efficiency choices on the drawing.

West of the Cascades, keep a covered entry

In a small plan every square foot counts, and the covered entry is the one most owners in western Washington are glad they kept. A roofed stoop deep enough to stand under, a bench and boot tray inside the door, and a hook wall for rain gear keep a small open plan from being the room where everything dries. Deep roof overhangs on the gable ends do the same job for the walls.

East of the Cascades, plan the lock and the roof

On the dry side the same entry works as a snow and dust lock, and a small building's roof is still drawn to the ground snow load the county sets in its own design table, which can be far higher in the mountains than in the Columbia Basin. A simple gable that sheds snow away from the door and the driveway is worth more than a dormer.

The tiny-house appendix

Under 400 square feet, Washington's code has its own appendix

Washington's residential code, chapter 51-51 WAC, adopts the 2021 International Residential Code and states that Appendix AQ, Tiny Homes, is included in that adoption. The appendix defines a tiny house as a dwelling unit of 400 square feet or less in floor area, excluding sleeping lofts, and lets habitable space in it have a ceiling height of 6 feet 8 inches, with bathrooms and kitchens at 6 feet 4 inches. Lofts in a tiny house follow Washington's own loft section, R333. Above 400 square feet, a small barndominium is simply a house under the full residential code, with the ordinary 7-foot ceiling rule for habitable rooms.

Common ways to build this

Three common ways to lay this out. Yours does not have to match one exactly — this is a starting point for the conversation, not a catalog.

One-room tiny house

16' x 24' / 384 sq ft / sleeping loft above

A single open room with a kitchen along one wall, a bathroom at one end and a sleeping loft over it, drawn under Appendix AQ at 400 square feet or less. The loft follows Washington's R333, and the entry gets a roofed stoop.

One-bedroom cottage

24' x 36' / 864 sq ft / covered porch on the long side

One bedroom with its own escape window, one bath, an open kitchen and living room under a vaulted ceiling, and a laundry by a mudroom entry. On the west side the porch runs along the long wall; on the east side it faces away from the prevailing winter wind.

Two-bedroom starter with a single bay

30' x 36' / 1,080 sq ft living / 400 sq ft enclosed bay under the same roof

Two bedrooms at one end and the living space at the other, with a single vehicle or equipment bay at the end of the building. Enclosed, the bay is a garage and needs the dwelling-garage separation from Table R302.6; open on at least two sides, it can be a carport.

Ways to build this

This layout can go together several ways. These are the service lines most relevant to it.

Barndominium Kits

Barndominium kits and shell kits for Washington State land: frame, panels and drawings, sized to the design values your city or county sets for the site.

Custom Plans

Custom barndominium plans for Washington State: floor plans and permit drawings with the energy code credits and your site's design values built in.

Pole Barn Homes

Pole barn homes and pole barn house kits for Washington State: post-frame buildings with a shop and living space, designed to your county's snow load.

Small Barndominium: common questions

6 questions worth settling before this plan is drawn. If yours is not on the list, put it in the survey.

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Is there a separate code for tiny houses in Washington?

There is an appendix rather than a separate code. Chapter 51-51 WAC includes Appendix AQ, Tiny Homes, in Washington's adoption of the International Residential Code. It covers dwelling units of 400 square feet or less, excluding sleeping lofts, and allows lower ceiling heights than a full-size house. Above that size the ordinary residential code applies.

Does a one-bedroom house need a smaller septic system?

Not below a set minimum. WAC 246-272A-0230 designs a single-family system on 120 gallons per bedroom per day, with a minimum design flow of 240 gallons per day, so one bedroom and two bedrooms start from the same number. The local health jurisdiction issues the permit and can require a larger design flow.

Can I put a small barndominium next to my existing house?

Whether a second home is allowed is a county or city zoning question, and rural zones differ from county to county, so start with the planning office. On the septic side, WAC 246-272A-0230 lets one additional dwelling share a system, designed at 120 gallons per bedroom for the second home on top of the first.

What ceiling height does a small barndominium need?

Under the 2021 International Residential Code as Washington adopts it, habitable rooms and hallways need at least 7 feet, and bathrooms, toilet rooms and laundry rooms at least 6 feet 8 inches. A tiny house of 400 square feet or less under Appendix AQ may have 6 feet 8 inches in habitable space and 6 feet 4 inches in bathrooms and kitchens.

What is the smallest practical barndominium footprint?

Most small barndominium plans start around 24 by 30 feet. Below that, fitting a bathroom, a kitchen, a laundry and a bedroom with a code-compliant escape window gets tight, and the escape window alone needs a clear opening of at least 5.7 square feet, or 5 square feet at grade level.

Do I still need to prove water for a small house?

Yes. RCW 19.27.097 requires every building permit applicant for a building that needs potable water to show evidence of an adequate water supply, such as a water purveyor's letter, a water right or, in many areas, a well report. In some river basins that evidence must also meet a specific streamflow rule. Size does not change the requirement.

Where this plan fits in Washington

West of the Cascades a plan answers to rain and seismic design; east of them, to snow, sun, dry acreage and wildfire. These are the areas this layout suits best.

Clallam County

A small house with a big covered entry suits the wet, windy north coast of the Olympic Peninsula.

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Mason County

Wooded rural parcels where a compact footprint keeps clearing, the drainfield and the well in proportion.

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Stevens County

East-side acreage where a small first house often comes before the shop, drawn for the county's snow load.

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Okanogan County

Remote dry-side land where a tight, simple plan is easier to heat, supply and protect from wildfire.

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Keep reading

The pages that answer the next question this one raises.

What size can your budget build?

How floor area, finish level and site work trade off before a small plan is chosen.

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Want this drawn for your program and your parcel? That is where a build actually starts.

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Sources

Code references on this page are to the 2021 International Residential Code as amended by Washington (chapter 51-51 WAC) and the 2021 Washington State Energy Code, Residential (chapter 51-11R WAC), in force since March 15, 2024. The State Building Code Council has scheduled the 2024 editions to take effect May 3, 2027; the edition your permit is reviewed under governs.

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Tell us what you want to build and we will draw this for your program, then confirm what it looks like on your parcel, which office permits it, and a realistic budget range. That conversation costs nothing.

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