New Building Code Regulations for Tiny Houses

By: David M. Kenney, AIA, NCARB

Tiny houses are small, stand-alone residential structures that have gained popularity in recent years.  They are typically used as a primary residence.  Tiny houses are also used as a lake or hunting cabin, or for other recreational activities.  They are generally constructed with a minimalist aesthetic, have an emphasis on simple living, and have a variety of aesthetically pleasing designs.  Small or tiny houses put an emphasis on design over size and utilize multi-purpose features and multifunctional furniture.  They incorporate space-saving equipment and appliances.  Vertical space is optimized with the use of living and sleeping lofts.

Although these small structures only make up less than 1% of real estate transactions in the country, they’ve generated everything from viral lists of the “Cutest Tiny Houses in Every State,” to reality shows such as Tiny House Nation and Tiny House Hunters.  The global tiny home market was expected to grow by about 4% in 2022, with most of that concentrated in the U.S.  The market is expected to hit $4.7 billion in global revenue by 2026.

Aside from popularity, the economics of living in a tiny house are also compelling.  Clearly, smaller houses are less expensive to live in than larger houses in terms of heating and cooling, maintenance, repairs, and taxes.  Regarding energy savings, a reduction of house size is the simplest way to lower energy consumption.

Tiny houses are also less expensive to construct.  For example, the average house in the U.S. uses approximately 17,300 board feet of lumber and 16,000 square feet of other wood products.  However, a 200 square foot tiny house uses approximately 1,400 board feet of lumber and 1,275 square feet of other wood products.  As of 2018, the average U.S. house cost approximately $358,000 to build, whereas the construction cost of a 200 square foot tiny house was approximately $35,000.

The increasing popularity of tiny houses suggests that such buildings should be regulated for the safety and welfare of their occupants, as with any other standard sized residence.  However, they are often not granted a building permit because of the difficulty in applying standard building code requirements to the design and construction of these small structures.  In this regard, the size of a house can make certain building code requirements more or less important.  The smaller size of a tiny house also makes its occupants more familiar with their surroundings, which results in a reduction in the need for certain standard building code requirements.  To that end, the 2018 edition of the International Residential Code introduced a new Appendix Q that addressed the specific requirements of tiny house design and construction.

The IRC/2018 Appendix Q limited the size of tiny houses to 400 square feet, which was based on the widely accepted maximum square footage for tiny houses in the construction industry.  That size limitation increases the difficulty in meeting certain dimensional requirements found in the main body of the IRC/2018 that are intended to regulate larger residential buildings.  However, years of experience in the design and construction of tiny houses has shown that, if reasonably designed and constructed, tiny houses can provide a safe living environment.  Further, by following certain dimensional parameters used in comparably sized “Recreational Park Vehicles” such as RV trailers that are governed by ANSI A119.1 and used in campgrounds and other seasonal use scenarios, alternative dimensions and other requirements for tiny houses were established to be considered safe for this residential use and were included in Appendix Q.

For example, the body of the IRC/2018 requires a 7-foot minimum ceiling height in habitable spaces.  Appendix Q reduced this minimum ceiling height to 6 feet 8 inches.  This is higher than the minimum of 6 feet 6 inches for Recreational Park Vehicles found in ANSI A 119.5, which has proven to provide a safe and sufficient headroom during extended occupancy of RV trailers.  Other reduced dimensions found in Appendix Q addressed stairways.  The body of the IRC/2018 requires a stair width of not less than 36 inches and stair risers not more than 7-3/4 inches tall.  Appendix Q permits tiny house stairs that are not less than 17 inches wide and have stair risers between 7 inches and 12 inches in height.  These dimensional requirements are identical to those found in ANSI A119.5 and was considered safe for the extended occupancy of RV trailers.  Also, the body of the IRC/2018 requires a stair headroom of not less than 6 feet 8 inches, whereas Appendix Q permits a stair headroom of not less than 6 feet 2 inches.  Because tiny houses are limited in area and height, the stair headroom height requirements found in the body of the IRC/2018 are often not achievable.  In this regard, Appendix Q stair headroom height was reasonably reduced.

Tiny houses can play a key role in reducing the environmental impacts of housing while lowering housing costs and providing home-ownership opportunities to a wider spectrum of the population.  However, a tiny house is not for everyone.  Some people, like basketball players, are just large and would not be comfortable living in a house with reduced dimensions.  Also, conditions like increased stair riser heights may not accommodate the abilities of certain people.

The IRC/2018 Appendix Q requirements for tiny house design and construction provide a new avenue for home ownership through reasonable alternative dimensions and other requirements that can offer safe and healthy homes for their owner.