The rules, in pictures
Light, a way out and alarms: the bedroom checklist
These are common model-code figures, drawn on real photos. They are how we check a design, not a permit, and the city's reviewer has the last word.
- 1
Light and air
Many codes ask for window glass equal to about 8% of the floor area, and an opening that is half of that. A dormer window usually carries this better than a skylight.
- 2
A way out
A bedroom needs a window you can climb through: about 5.7 sq ft of clear opening, and a sill no higher than 44 in. A fixed skylight does not count.
- 3
Alarms
Smoke alarms go inside the bedroom, outside it and on every level, wired so that one sounds all of them.
Figures differ by code year. We confirm them against the code the city applies to your permit.
The stair
Five numbers on every stair we draw
A stair is the part of an attic job that gets checked most closely, and the part you'll use every day.
- 1
Headroom
6 ft 8 in, measured straight up from the line of the stair's front edges, along the whole run.
- 2
Handrail
34 to 38 in above that same line, round or oval so a hand can close around it.
- 3
Gaps
No opening wide enough to pass a 4 in ball between balusters, so a child's head can't pass.
- 4
Risers and treads
Risers no taller than 7¾ in and treads at least 10 in deep, with every step within ⅜ in of the others.
A stair that already exists in an old house is judged differently from a new one. The city's reviewer decides which applies.
Stair shapes
Three ways to reach an attic
The shape depends on how much room the floors below can give.
| What to know | L-shaped or winder | Alternating-tread stair | Straight run |
|---|---|---|---|
| Room it takes | L-shaped or winderShorter along the wall, wider across the house | Alternating-tread stairThe smallest footprint of the three | Straight runThe longest: often 11 or 12 ft of run for a typical floor height |
| Comfort | L-shaped or winderEasy once built, but the turn costs headroom if drawn badly | Alternating-tread stairSteep, with a staggered step you learn to use | Straight runEasiest to climb and to carry furniture up |
| What codes say | L-shaped or winderAccepted; winders must keep a minimum tread depth at the narrow end | Alternating-tread stairOften limited to a loft; we ask the city before we draw one for a bedroom | Straight runAccepted everywhere the rules above are met |
| Where it fits | L-shaped or winderA narrow house where a hall can't be spared | Alternating-tread stairRarely our first choice | Straight runA wide house, or a stair that can take over a hall |
Questions
Rules we get asked about
Are these the exact rules for my house?
No. They are common figures from the model residential code, and the city adopts and amends it. We draw to the rule the city applies at your address and say so on the sketch.
What if my attic is just under seven feet?
Then the question is how much of the floor reaches it. A dormer on one side often turns a narrow strip of full height into a usable room, and we'll draw that against a pop-up so you can compare.
Can the existing hatch ladder stay?
As a way into storage, yes. As the way into a bedroom, no. A bedroom needs a proper stair.
Who decides if a design passes?
The city's plan reviewer and inspector. We prepare the drawings and meet the inspector on site.
Bring a tape measure, or let us bring ours
Tell us the tallest point and where the stair goes now. We'll take it from there.