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.
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.
Section R304 – Minimum Room Areas
R304.1 Minimum area. Every dwelling unit shall have at least one habitable room that shall have not less than 120 square feet (11 m2) of gross floor area.
R304.2 Other rooms. Other habitable rooms shall have a floor area of not less than 70 square feet (6.5 m2). Exception: Kitchens.
R304.3 Minimum dimensions. Habitable rooms shall not be less than 7 feet (2134 mm) in any horizontal dimension. Exception: Kitchens.
R304.4 Height effect on room area. Portions of a room with a sloping ceiling measuring less than 5 feet (1524 mm) or a furred ceiling measuring less than 7 feet (2134 mm) from the finished floor to the finished ceiling shall not be considered as contributing to the minimum required habitable area for that room.
Section R305 – Ceiling Height
R305.1 Minimum height. Habitable space, hallways, bathrooms, toilet rooms, laundry rooms and portions of basements containing these spaces shall have a ceiling height of not less than 7 feet (2134 mm).
- For rooms with sloped ceilings, at least 50 percent of the required floor area of the room must have a ceiling height of at least 7 feet (2134 mm) and no portion of the required floor area may have a ceiling height of less than 5 feet (1524 mm).
Bathrooms shall have a minimum ceiling height of 6 feet 8 inches (2032 mm) at the center of the front clearance area for fixtures. The ceiling height above fixtures shall be such that the fixture is capable of being used for its intended purpose. A shower or tub equipped with a showerhead shall have a minimum ceiling height of 6 feet 8 inches (2032 mm) above a minimum area 30 inches (762 mm) by 30 inches (762 mm) at the showerhead.
R305.1.1 Basements. Portions of basements that do not contain habitable space, hallways, bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6 feet 8 inches (2032 mm). Exception: Beams, girders, ducts or other obstructions may project to within 6 feet 4 inches (1931 mm) of the finished floor.
Section R306 – Sanitation
R306.1 Toilet facilities. Every dwelling unit shall be provided with a water closet, lavatory, and a bathtub or shower.
R306.2 Kitchen. Each dwelling unit shall be provided with a kitchen area and every kitchen area shall be provided with a sink.
R306.3 Sewage disposal. All plumbing fixtures shall be connected to a sanitary sewer or to an approved private sewage disposal system.
R306.4 Water supply to fixtures. All plumbing fixtures shall be connected to an approved water supply. Kitchen sinks, lavatories, bathtubs, showers, bidets, laundry tubs and washing machine outlets shall be provided with hot and cold water.
Section R307 – Toilet, Bath and Shower Spaces
R307.2 Bathtub and shower spaces. Bathtub and shower floors and walls above bathtubs with installed shower heads and in shower compartments shall be finished with a nonabsorbent surface. Such wall surfaces shall extend to a height of not less than 6 feet (1829 mm) above the floor.