The room has a single fixed window with 4 square feet of glazing that does not open. Judging the room against the natural light and ventilation option, what is the finding?
- AIt complies; 3 square feet of glazing is required and this window provides 4 square feet
The glazing area is only half the requirement. Openable area is a separate condition and this window provides none of it.
- It fails; half the required 3 square feet must be openable, so 1.5 square feet of openable area or a fan is needed
- CIt complies; fixed glazing is acceptable in a bathroom because the door provides the air exchange the room needs
A door is not ventilation to the outdoors and is not credited. It moves moisture into the rest of the house rather than out of the building.
- DIt fails; a bathroom requires 8 percent of its floor area in glazing, the same as any other habitable room
Eight percent applies to habitable rooms. A bathroom is not a habitable room, and it has its own smaller fixed requirement with the mechanical alternative.
Why B is correct
Bathrooms taking the natural option need at least 3 square feet of glazing with not less than half of that openable, which is 1.5 square feet. Fixed glazing provides none, so the window must be replaced with an operable unit or mechanical exhaust must be installed at the required rate.
What this question is testing
Whether the candidate knows the bathroom natural light and ventilation option has both an area and an openable portion, and does not apply habitable room percentages to a bathroom.
On the job
Fixed decorative windows in bathrooms are common in production housing and in remodels where privacy glass was chosen from a catalog. Inspectors check whether the sash opens before doing any arithmetic. Where it does not, the practical fix at the final is a fan, since replacing the window means opening the exterior wall, and the fan then brings its own requirement to terminate outdoors.
Memory technique
Three and a half of three.
Exam tip
Three square feet of glass, half of it openable, or install a fan instead.
Where to look it up
IRC Chapter 3, light and ventilation, the bathroom paragraph with its mechanical alternative.