Turning a basement room into a bedroom is one of the most common finish jobs a small contractor bids, and egress is the item that sinks it at inspection. The International Residential Code treats a sleeping room as a place someone has to be able to get out of in a fire, and a firefighter has to be able to get into. In a basement that usually means cutting the foundation, setting a larger window and digging a well. Here is what the model code asks for, section by section.
When an egress opening is required (R310.1)
Every sleeping room needs at least one operable emergency escape and rescue opening (EERO) that opens directly to the outside. Basements with habitable space need one too, and where a basement has sleeping rooms, each sleeping room needs its own. The opening has to work from the inside without keys, tools or special knowledge, so a locking bar or a removable grille that needs a wrench does not count.
There is a narrow exception for a basement used only to house mechanical equipment and not exceeding 200 square feet. Once you finish the space or someone sleeps there, plan on the requirement.
Minimum opening size (R310.2.1)
- Net clear opening of at least 5.7 square feet. Grade-floor openings may be 5.0 square feet.
- At least 24 inches of clear opening height.
- At least 20 inches of clear opening width.
Those three numbers have to be met together. A 24-inch by 20-inch opening is only about 3.3 square feet, so a window at the minimum height must be wider than 20 inches to reach 5.7, and the reverse is also true. The measurement is the net clear opening with the sash open, not the rough opening and not the glass size. Casements usually get there in a smaller unit than sliders or double-hungs, because the whole sash swings out of the way.
Sill height (R310.2.2)
The bottom of the clear opening can sit no more than 44 inches above the finished floor. In a basement with a high foundation wall that often means lowering the opening, which is why so many basement egress jobs start with a saw cut in the concrete.
Window wells (R310.2.3) and ladders (R310.2.3.1)
When the sill is below grade, the window needs a well. The well must give at least 9 square feet of horizontal area, with at least 36 inches of width and 36 inches of projection out from the wall, and it has to let the window open fully. A well deeper than 44 inches needs a permanently fixed ladder or steps usable with the window open: rungs at least 12 inches wide, projecting at least 3 inches from the wall, and spaced no more than 18 inches apart vertically.
Line items to price on a basement egress job
Every one of these lines is a quantity you can take off and price for your market. Skipping any of them is how an egress window turns into a loss:
- Layout and locating utilities before any cutting.
- Excavation for the well, including hand digging near the foundation where needed.
- Saw-cutting the foundation opening, and the header or lintel the new opening requires.
- The egress window unit, sized to the net clear opening and not the rough opening.
- Window well, ladder or steps where the well is over 44 inches deep, and any cover.
- Drainage at the bottom of the well, tied into the footing drain or gravel as the design calls for.
- Waterproofing, flashing and sealing around the new opening.
- Interior returns, trim and finish around the window.
- Demolition debris and haul-off.
- Permit and inspections.
Section numbers move between editions
The section numbers above follow the 2015 and 2018 IRC numbering that the cited library answers use. Later editions reorganize parts of R310, and states and cities adopt the code with their own amendments. Before you cut concrete, confirm with your local building department which edition they enforce and whether they have amended any of these sizes.
Size the opening, not the window. The inspector measures the clear opening with the sash open, so price the unit that clears 5.7 square feet, 24 inches high and 20 inches wide at the same time.