Tiny house laws by state: Appendix Q, wheels and the 400-square-foot line

Build a 300-square-foot house on a trailer to the RV or park model standard and take it to Maine, and state law calls it a “tiny home,” a vehicle that towns must allow wherever a single-family house is allowed. Drive the same house to New Mexico and the state residential code says it is a recreational vehicle for as long as the axle stays on. Take it to New Hampshire after September 13, 2026, and a new law says a tiny house on wheels built for living in is not a camp trailer or RV at all.

Those three answers come from three states that have actually thought about the question. Most have not. We checked the residential code adopted in every state for the national tiny house appendix and for any law on tiny homes on wheels. Only 19 states have written the appendix into a code they apply statewide. Two of those quietly changed the 400-square-foot limit that defines a tiny house: Hawaii raised it to 500 and New Hampshire to 600.

Three states, three answers

The reason a tiny house is hard to regulate is that it sits on the border between categories the law already has. On a foundation it is a small house, so the residential building code applies. On a trailer it looks like a recreational vehicle, which is built to an industry standard and regulated mostly as a vehicle. Factory-built on a steel chassis and bigger than 320 square feet, it can meet the federal definition of a manufactured home. Each category comes with a different inspector, a different label, a different set of zoning rules and a different answer to the only question most owners care about: can I live in it full time?

• Maine defines a tiny home as a living space of no more than 400 square feet, permanently built on a frame or chassis, designed for permanent living, built to the park model (ANSI A119.5) or RV (NFPA 1192) standard and without its own engine. Since 2021 30-A MRSA §4363 says a town “shall permit” one on any lot where single-family homes are allowed, or as an accessory structure, subject to the same land use rules.
• New Mexico rewrote the appendix in its 2021 Residential Building Code (14.7.3.28 NMAC). Tiny houses “constructed on a chassis with permanent axle shall be considered recreational vehicles” and licensed as RVs while the axle remains. Remove the axles and set the house on a foundation, and it must meet the residential code, including the tiny house appendix.
• New Hampshire passed HB 1681 (Chapter 330, signed July 15, 2026, effective September 13, 2026). It defines a “tiny house on wheels” as a tiny house on a trailer chassis without motive power and says it “shall not be considered a camp trailer or recreational vehicle when constructed for human habitation.” Towns may treat tiny houses, tiny houses on wheels and yurts as single-family homes or accessory dwelling units.

Federal law, the model building code and the RV industry each draw their own lines, and most states have simply inherited them. The rest of this article walks through those lines and then through what every state has done with the one tool written specifically for tiny houses.

What the tiny house appendix changes

The International Residential Code (IRC) is the model code most states and counties use for one- and two-family homes. It was written for ordinary houses, and several of its rules are hard to meet in 250 square feet: a full stairway with 6 feet 8 inches of headroom to reach a sleeping loft, 7-foot ceilings in habitable rooms, and an emergency escape window in every sleeping room.

The fix began as a rejected proposal. According to the International Code Council’s own account, a retired Oregon building official proposed tiny house exemptions in April 2016, and the committee voted it down but suggested an appendix instead. Builder Andrew Morrison and architect Martin Hammer, who had co-written the IRC’s straw bale appendix, assembled a volunteer team and submitted a full appendix as a public comment for the October 2016 hearings in Kansas City. Building officials testified that residents were already calling them about tiny houses. In the December 2016 vote it passed with “just over two-thirds in favor,” and code change RB168-16 became Appendix Q of the 2018 IRC.

The appendix has changed its letter with each edition, which confuses many searches and some local officials:

A tiny house under the appendix is a dwelling of 400 square feet or less, excluding lofts. Using the model text as published in Seattle’s 2021 code, the main relaxations are:

• Ceilings. Habitable space and hallways need 6 feet 8 inches; bathrooms, toilet rooms and kitchens 6 feet 4 inches. Lofts may be lower.
• Lofts. A loft is a level more than 30 inches above the main floor, open on at least one side, with a ceiling under 6 feet 8 inches. It must have at least 35 square feet and be at least 5 feet in every horizontal direction. Floor area under a sloped ceiling lower than 3 feet does not count.
• Getting up there. Loft stairs may be 17 inches wide at the handrail and 20 inches below it, with 6 feet 2 inches of headroom and risers of 7 to 12 inches. Ladders are allowed, with rungs at least 12 inches wide, spaced 10 to 14 inches apart, rated for 300 pounds and set at 70 to 80 degrees. Alternating tread devices and ship’s ladders are allowed at 20 inches wide.
• Guards. Open loft edges need a guard 36 inches high or half the clear height to the ceiling, whichever is less.
• Escape. A skylight or roof window in a loft used for sleeping can count as the emergency escape and rescue opening, if installed to the appendix’s rules.

What it does not relax matters as much. Everything else in the residential code still applies: foundation, structure, wind and snow loads, insulation, smoke alarms, plumbing, electrical and fire separation. A tiny house under the appendix is a real house, with the permit, inspections and certificate of occupancy a real house needs. The 2021 edition added an energy section with an air-leakage test and whole-house ventilation, which California and Washington both chose to drop or rewrite.

The 2024 IRC went further in one respect. It added a sleeping loft section to the body of the code (R315 in the model numbering), so any house can now have a sleeping loft of less than 70 square feet, with its own reduced rules for ceiling height and access, as the Washington State Building Code Council’s review of the 2024 text shows. The tiny house appendix itself stayed an appendix, renamed BB.

Which states adopted it

An IRC appendix does nothing by itself. The model text says so at the top of the page: its provisions “are not mandatory unless specifically referenced in the adopting ordinance.” A state that adopts “the 2021 IRC” has not adopted Appendix AQ unless its rule names it. That is why so many tiny house guides get state status wrong: they read “adopted the IRC” as “adopted the tiny house rules.”

Three patterns explain most of the map.

States that write one code for everyone tend to include it. New Jersey, New York, Rhode Island, Maryland, Connecticut, Virginia and Massachusetts all apply a single state code in every town, and all of them have taken the appendix in. Their adopting rules usually list the appendices by letter; Connecticut’s names nine, including AQ. Minnesota deletes every IRC appendix except two, and one of them is the tiny house appendix. Utah went further and put Appendix AQ into statute.

Some states pass it down. Georgia, Oklahoma, Montana and West Virginia have state codes but leave the appendix for cities and counties to adopt. Oklahoma’s 2024 rule, effective September 14, 2026, declines Appendix BB in so many words and says local jurisdictions may adopt it. Georgia’s Department of Community Affairs publishes a sample ordinance for counties that want it. Montana applies the appendix itself only to factory-built tiny houses headed for a permanent foundation.

Home-rule states have no state answer at all. In Arizona, Colorado, Kansas, Missouri, Texas, Wyoming and the other states without a statewide residential code, whether you can use the appendix depends entirely on the county. In many rural counties there is no residential building code to amend, which cuts both ways: no appendix, but often no building inspection either. Our article on counties without building codes explains what still applies there, from septic permits to lenders.

A few results are surprising. Idaho was one of five states the ICC listed in 2018 as having adopted or begun adopting Appendix Q, but the current Idaho Residential Code adopts only four parts of the 2018 IRC and does not list it. Iowa moved to the 2024 IRC in August 2026 and deleted every appendix. Kentucky’s residential code is still based on the 2015 IRC, which predates the appendix. And North Carolina, whose code is also based on the 2015 IRC, wrote its own Appendix Q in 2021 and adopted it statewide.

All 50 states

Each row shows whether the state’s residential code includes the tiny house appendix, which code is in force, what we found on tiny homes on wheels, and the official source for the status. “Local option” means the state code exists but leaves the appendix to local governments. “No statewide code” means counties and cities choose their own building codes, if any; see counties without building codes and our building codes by state table. Where we could not open the adopting rule, the status says so.

Status checked October 2026 against each state’s adopting rule, statute or agency publication, linked in each row. “No state tiny-home-on-wheels category found” means we found no state statute or rule creating one; federal RV, park model and HUD rules still apply, and local zoning decides occupancy. Statewide adoption does not override local zoning, and local governments in “no statewide code” states may have adopted the appendix on their own.

Tiny homes on wheels: four federal boxes

The appendix only covers houses on foundations. A tiny house on a trailer lands in one of four existing categories, and the label on the unit, not the way it looks, decides which.

1. Recreational vehicle (NFPA 1192)

The RV Industry Association defines an RV as a vehicle-type unit designed as temporary living quarters for recreational, camping or seasonal use, regulated by NHTSA as a vehicle, movable without a special highway permit, and certified by the manufacturer to the NFPA 1192 standard. A tiny house can qualify if it is built as a vehicle to federal motor vehicle safety standards and the RV standard. RVIA inspects member factories about every eight weeks.

2. Park model RV (ANSI A119.5)

A park model RV is built on a single chassis on wheels, certified to ANSI A119.5, and has a gross trailer area of no more than 400 square feet in setup mode. If it is smaller than 320 square feet, RVIA says it must be wide enough to need a special highway movement permit; otherwise it would simply be an RV. RVIA’s policy page states that park models “are neither designed nor intended by their manufacturers to be used as permanent residences.”

3. HUD manufactured home

Federal law defines a manufactured home as a structure transportable in one or more sections that is 8 body feet or more wide or 40 body feet or more long in traveling mode, or 320 or more square feet when erected on site, built on a permanent chassis and designed as a dwelling with or without a permanent foundation. A tiny house on a trailer chassis that crosses 320 square feet falls inside that definition unless an exemption applies. The exemption that matters is 24 CFR 3282.15: a recreational vehicle is exempt if it is not certified as a manufactured home, is “designed only for recreational use and not as a primary residence or for permanent occupancy,” and is certified to NFPA 1192 or ANSI A119.5 (or is self-propelled). Park model sellers must display a manufacturer’s notice saying exactly that.

That is the trap at the heart of tiny house law. The federal exemption that keeps a tiny house on wheels out of the HUD code depends on it not being designed as a primary residence, which is what most buyers want it for. RVIA says it plainly: if a manufacturer markets tiny homes as permanent residences, “these units cannot be considered RVs or PMRVs,” and must instead comply with local building codes, state modular codes or HUD rules.

4. State factory-built or modular approval

The fourth route treats the tiny house as a small house built in a factory. A state agency reviews the plans, inspects the plant and attaches an insignia; the local building department then permits only the foundation, utilities and placement. The ICC’s model tiny house legislation recommends exactly this, using the IRC with the tiny house appendix plus the ICC/MBI 1200 and 1205 off-site construction standards, for any tiny house “designed to be used as permanent or primary residences regardless of their ability to be moved.” Washington puts factory-built tiny houses “with or without a chassis (wheels)” under the Department of Labor and Industries, which issues an insignia. Colorado’s HB22-1242 brought off-site-built tiny homes under the state’s factory-built housing program. New Hampshire’s 2026 law lets builders choose either local inspection or the state modular program, and requires the local official at the destination to accept the approval.

States that wrote their own tiny house laws

Beyond building codes, a handful of states have passed laws aimed squarely at tiny houses. They take two approaches: deciding what a tiny house on wheels is, and stopping local zoning from shutting small homes out.

Notice that Maine and New Hampshire, neighbors, went in different directions. Maine wrote its tiny home definition into the motor vehicle title and tied it to RV standards, then told towns to accept the result. New Hampshire wrote its definition into the planning statute, made a tiny house on wheels a building rather than a vehicle, and routed inspection through the building code or the modular program. Maine’s approach is easier for owners of existing RV-certified units. New Hampshire’s gives towns a building-code inspection they can rely on, which is what lenders and insurers usually want.

Not every bill passes. A 2025 Texas bill, SB 2413, that would have defined tiny homes and tiny home communities was referred to committee and went no further.

Why 400 square feet keeps coming up

The number in this article’s title is not a coincidence of round figures. Several unrelated rules converge on it, and a project that sits just above or below it can change category.

• The building code. The tiny house appendix covers 400 square feet or less, excluding lofts. At 401 square feet the full IRC applies, with standard stairs to any loft and standard ceiling heights, unless your state changed the number. Hawaii’s State Residential Code uses 500 square feet and New Hampshire’s 2024 amendments use 600.
• The park model RV. ANSI A119.5 units top out at 400 square feet in setup mode. A larger trailer-built unit cannot be a park model.
• Maine’s tiny home. The statutory definition stops at 400 square feet.
• The HUD threshold below it. At 320 square feet erected, a unit on a permanent chassis meets the size test for a manufactured home. Between 320 and 400 square feet, a trailer-built tiny house is either a park model RV, a HUD home or, in a few states, a state-approved factory-built house. Which one is decided by its certification label.
• Local minimum dwelling sizes. Many zoning codes set a minimum floor area for a house, often well above 400 square feet, which rules out a code-compliant tiny house no matter how it was built. North Carolina and Connecticut are among the few states that have banned or limited those minimums by statute; elsewhere, check the zoning ordinance before anything else.

Financing and insurance follow the same categories. A house on a permanent foundation with a certificate of occupancy is generally mortgaged and insured like other homes. An RV or park model is usually financed and insured as a vehicle. A tiny house on wheels with no recognized label may fit neither, which leaves cash, personal loans and specialty insurers.

Before you buy or build

Work through these in order. The first answer narrows every one after it.

1. Decide foundation or wheels. If you plan to live in it permanently on one parcel, a foundation is the route most likely to end in a legal, insurable, financeable home. Wheels make sense if you will genuinely move it, or if the parcel allows RV occupancy.
2. On a foundation: find out whether your state code includes the appendix (table above), and if not, whether the county has adopted it. Without it, design to the full residential code: standard stairs, 7-foot ceilings and a conventional egress window in every sleeping room.
3. On wheels: decide which label you are buying (RVIA seal, park model notice, HUD label or a state insignia), then confirm the county will allow that category to be lived in on your land, for how long, and with what wastewater connection.
4. Either way: get the septic or wastewater permit and water source sorted before you buy the unit. A tiny house still needs an approved place for its sewage; our septic and composting toilet guide covers the options.

Questions for the building and zoning office

• Which residential code edition do you enforce, and have you adopted the tiny house appendix (Q, AQ or BB)? If not, will you accept it as an alternative method?
• Is there a minimum dwelling size in my zoning district? Does it apply to accessory dwellings?
• Is a tiny house on wheels a dwelling, an RV or something else here? Can it be occupied full time, and is there a time limit?
• Will you accept a state factory-built insignia, an RVIA seal or a third-party certificate as proof of construction, or do you need to inspect?
• If I remove the wheels and set it on a foundation, what inspections will you require for work that is already closed in?
• What does the health department need for septic, well and graywater before you issue a permit?

Labels to ask a builder for

A unit with no label at all, built in a backyard or by a small shop, is the hardest to approve after the fact. Officials cannot inspect inside closed walls, so the usual choices are opening them up, an engineer’s report or living in it as something other than a home. For more on placement and occupancy, see our guides to tiny homes and RVs and buying off-grid land, and our article on living in an RV on your own land.