The window serving a first-floor bedroom is a grade floor opening. With the sash raised, the openable portion measures 30 inches wide by 24 inches high, and the framed rough opening for the unit measures 34 inches by 30 inches. The minimum net clear opening for a grade floor opening is 5.0 square feet, the minimum clear height is 24 inches and the minimum clear width is 20 inches. How should the inspector rule?
- AThe clear height of 24 inches falls below the minimum, so a taller unit is required
The measured clear height is 24 inches, which equals rather than falls below the minimum. Minimums are satisfied when the measurement lands exactly on the number.
- BThe net clear opening is 5.0 square feet, which falls short of the 5.7 square feet required of every escape and rescue opening no matter where it is located
The 5.7 square foot figure applies to escape and rescue openings other than those at the grade floor or below grade. Reading it as universal makes a compliant grade floor window look short.
- The net clear opening is exactly 5.0 square feet and both clear dimensions are satisfied, so the window is acceptable
- DThe opening measures 7.08 square feet, so it clears the requirement with room to spare
Rough opening dimensions include the frame, the sash stiles and the sill. None of that is clear opening, and using it overstates the escape area by more than 40 percent here.
Why C is correct
Work the openable dimensions: 30 times 24 equals 720 square inches; 720 divided by 144 equals 5.0 square feet. The grade floor allowance is 5.0 square feet, so the area is met at the exact limit. Clear height equals the 24-inch floor and clear width comfortably beats the 20-inch floor. All three criteria are independent, and this unit satisfies each of them.
What this question is testing
The item tests three things at once: measuring net clear opening from the openable sash rather than the rough opening, knowing that the grade floor and below-grade allowance is 5.0 square feet, and treating area, clear height and clear width as three separate tests that must each be met.
On the job
Window suppliers publish clear opening data in their catalogs, and builders quote it at you on site. The inspector's job is to verify it with a tape through the actual raised sash, because a unit ordered right can still be installed with a stop screw, a shipping block or a factory limiter left in place. Grade floor openings are where the 5.0 square foot allowance saves a job, and where an inspector who insists on 5.7 across the board writes an unenforceable correction. Know which number belongs to which opening before you speak on site.
Memory technique
Five-seven for the upstairs, five-flat at grade.
Exam tip
Read the question for the words grade floor or below grade before you pick between 5.0 and 5.7 square feet.
Where to look it up
IRC Chapter 3, emergency escape and rescue openings, the opening area and dimension subsections.