The International Residential Code (IRC) sets a handful of minimum dimensions for every house: how big a habitable room must be, how high its ceiling, how wide a hallway, stair or entry door. They matter most when you finish a basement or attic, convert a garage, or plan an addition, because an inspector will check them and a room that misses them cannot be called a bedroom. This guide lists the 2021 IRC minimums in one place, with the exceptions that most often apply.
Minimum dimensions at a glance (IRC 2021)
| Item | Minimum | IRC section |
|---|---|---|
| Habitable room size | At least 70 sq ft of floor area | R304.1 |
| Room dimension | No habitable room less than 7 ft in any horizontal direction (kitchens excepted) | R304.2 |
| Counting sloped ceilings | Floor area under a ceiling lower than 5 ft does not count toward the minimum room area | R304.3 |
| Ceiling height, habitable rooms and hallways | At least 7 ft | R305.1 |
| Ceiling height, bathrooms, toilet rooms, laundry rooms | At least 6 ft 8 in | R305.1 |
| Sloped ceilings | At least half the required floor area must have a 7 ft ceiling, and no part under 5 ft counts | R305.1 exception |
| Bathroom fixtures under a sloped ceiling | Each fixture must be usable for its purpose; a shower or tub with a showerhead needs 6 ft 8 in over a 30 x 30 in area at the head | R305.1 exception |
| Beams, ducts, pipes in basements with habitable space | May project to within 6 ft 4 in of the finished floor | R305.1 exception |
| Basement areas without habitable space or hallways | At least 6 ft 8 in, with beams, girders and ducts down to 6 ft 4 in | R305.1.1 |
| Egress door | At least one side-hinged exterior door with at least 32 in of clear width (door open 90 degrees, measured face of door to stop) and at least 78 in of clear height | R311.2 |
| Hallway width | At least 3 ft (36 in) | R311.6 |
| Stair width | At least 36 in clear above the permitted handrail height | R311.7.1 |
| Stair width at handrails | Handrails may project up to 4-1/2 in from each side; clear width at and below the rails at least 31-1/2 in with one rail, 27 in with two | R311.7.1 |
| Stair headroom | At least 6 ft 8 in, measured vertically from the sloped line of the nosings | R311.7.2 |
Smallest rooms that meet the size rules
| Width | Shortest length | Floor area |
|---|---|---|
| 7 ft | 10 ft | 70.0 sq ft |
| 7.5 ft | 9 ft 4 in | 70.0 sq ft |
| 8 ft | 8 ft 9 in | 70.0 sq ft |
| 8.5 ft | 8 ft 3 in | 70.1 sq ft |
| 9 ft | 7 ft 10 in | 70.5 sq ft |
| 10 ft | 7 ft | 70.0 sq ft |
A habitable room is any space for living, sleeping, eating or cooking. Bathrooms, closets, hallways, laundry and utility rooms are not habitable rooms, so the 70 sq ft and 7 ft rules do not apply to them, although the ceiling height rules do. A bedroom also needs an emergency escape opening; see the egress window size guide.
Ceiling height in basements and attics
- Finished basements: a basement room used as a bedroom, family room or office is habitable space and needs a 7 ft ceiling (R305.1), with beams, ducts and pipes allowed down to 6 ft 4 in. An unfinished basement with no habitable space may be 6 ft 8 in (R305.1.1).
- Attic rooms: at least half of the required floor area needs a 7 ft ceiling, and floor area where the ceiling is under 5 ft is not counted. Example: an attic room 12 ft wide between 4 ft knee walls, with a ceiling that rises at 12/12 from the walls, reaches 5 ft one foot in from each wall and 7 ft three feet in, so only the central 6 ft of width has a 7 ft ceiling. For a 70 sq ft room that strip must be at least 35 sq ft and the counted area (10 ft wide) at least 70 sq ft: a room at least 7 ft long passes.
- Bathrooms: the general minimum is 6 ft 8 in. Under a sloped ceiling each fixture must still be usable, and a shower or tub with a showerhead needs 6 ft 8 in over a 30 x 30 in area at the head. Fixture spacing is covered in the toilet clearance guide.
Hallways, stairs and doors
Hallways must be at least 36 in wide (R311.6). Stairs need 36 in of clear width above the handrail, and the handrails may eat into it by up to 4-1/2 in each side, leaving at least 31-1/2 in with one rail or 27 in with two (R311.7.1). Headroom over the stair is at least 6 ft 8 in. At least one exterior door must give a clear opening of 32 in by 78 in (R311.2), which in practice means a 36 in door slab; interior doors have no IRC minimum width, although 30 to 32 in doors are common and wider doors help with furniture and wheelchairs. For risers and treads use the stair calculator, and for rail heights the handrail and guard height guide.
Frequently asked questions
What is the minimum ceiling height in a house?
7 ft for habitable rooms and hallways and 6 ft 8 in for bathrooms, toilet rooms and laundry rooms under IRC R305.1, with exceptions for sloped ceilings and, in basements, beams and ducts down to 6 ft 4 in.
What is the minimum bedroom size?
At least 70 sq ft and at least 7 ft in every horizontal direction (IRC R304.1, R304.2), with a 7 ft ceiling and an egress window or door.
How wide does a hallway have to be?
At least 36 in under IRC R311.6. For wheelchair use, the ADA Standards use 36 in of clear width as the minimum continuous route, with 60 in where wheelchairs must turn or pass.
What is the minimum width of stairs?
36 in of clear width above the handrail, and at least 31-1/2 in at the handrail with one rail or 27 in with two (IRC R311.7.1).
Can a basement have a 6 ft 8 in ceiling?
Only if it has no habitable space. A finished basement bedroom or family room needs 7 ft, with beams and ducts allowed down to 6 ft 4 in.
Sources
- International Code Council, 2021 International Residential Code (IRC). Requirements are paraphrased with their section numbers; local codes and amendments may differ, so confirm with your building department.
- 2010 ADA Standards for Accessible Design (US Department of Justice), sections 403.5.1 and 304 (accessible routes and turning space), for the wheelchair figures in the FAQ.
Last reviewed: 24 October 2026. Numbers in the tables are our arithmetic from the sources listed; code sections are summarised, not quoted. How we check our work: methodology and corrections. Spotted an error? Please let us know.