If you want to build a tiny house on the ground, then it’s a good idea to start with the International Residential Code’s (IRC) minimum size requirement: 120 square feet measured from interior faces of exterior walls.
Please buckle your seat belt to learn more about IRC habitable space, minimum areas and ceiling heights. These codes are revised and reviewed by the International Code Committee (ICC), and are known throughout the U.S.
Here’s a new yet classic cottage based on the Whidbey design from Tumbleweed Houses. Sporting 960 square feet, the Great Barrington riverside home is now for re-sale. (realtor.com)
Welcome to minimum codes
Let’s begin with a confusing but true statement: while all the minimums apply to habitable spaces, habitable spaces are defined by meeting minimums too.
In typical houses, all living, sleeping, eating or cooking areas qualify as habitable spaces. Bathrooms, toilet rooms, closets, halls, storage or utility spaces aren’t defined as habitable, for any dwelling. Here are minimum room sizes:
- Minimum area. One habitable room that’s at least 120 square feet.
- Other rooms. At least 70 square feet.
- Minimum dimensions. At least 7 feet in any horizontal dimension.
- Height effect on room area. At least 7 feet high. If sloped, also over 5 feet.
Tom Meyers, past chairman of ICC’s residential code committee, explains height requirements for a habitable room:
“The IRC requires 7 feet vertical clearance except when the ceiling is sloped. When the ceiling is sloped, only one half of the required room area must be provided with the 7 foot headroom clearance. If the room is required to be 70 sf in area, then 35 sf of the room must have 7 feet of clearance. Additionally, all the remaining required area must have a minimum of 5 feet of clearance.”
There are some exclusions and exceptions. Notably, kitchens are excluded from the other room, dimensions and height effect codes. Also bathrooms only need to be 6 feet, 8 inches tall, to accommodate fixtures.
Sleeping lofts are not “habitable” areas
In a tiny or small house, an upstairs loft typically won’t qualify as a habitable bedroom, so you may access it with a ladder or non-compliant egress. Tom Meyers offers clear advice:
“If you are ever challenged on the use of a ladder for non-habitable loft, be assured that the code allows it by default. Intentionally, there are no requirements for non-habitable loft access. I know this as I am the one that wrote this code section.”
“The code official is unlikely to allow you to use your non-habitable loft for compliance with permanent provision for sleeping. Best to figure out a way to put a bed (fold out or otherwise) on the lower level.”
Rural, suburban and urban code approvals
When living in a more populated area, you should expect larger and different minimum sizes in your local building and zoning codes. Please check with your City Hall while planning a single home or secondary dwelling unit build on your property. Otherwise your house could be unusable!
Are all these codes necessary? Suburban and urban people live with many codes because they’re not contemplating “daily survival,” muses Tom Meyers. By contrast, rural areas are more lax and may not even have codes because “they don’t need to be told what they already know.”
More Information: Please check out exact wording of the International Code Council (ICC) minimums below, covering Minimum Room Areas, Ceiling Height, Sanitation, and Toilet, Bath and Shower Spaces.