The Minimums
The IRC sets four size numbers for the window itself: 5.7 square feet of clear opening (5.0 square feet when the sill is within 44 inches of outside grade), at least 20 inches of clear width, at least 24 inches of clear height, and a sill no more than 44 inches above the floor. Clear opening means the actual hole you climb through with the window fully open — not the size of the frame on the box it came in.
Why "Clear Opening" Trips People Up
A 32-by-48 window sounds big enough, right? Not necessarily. On a double-hung window, only half the window opens — so a 32-inch-wide double-hung gives you about 16 inches of clear width, which fails the 20-inch minimum. On a slider, half opens too. That is why casement windows (which swing fully open) are the most common egress choice: the whole window becomes the opening. Read our casement vs. slider guide for the full comparison.
The Sill Height Rule
The sill — the bottom of the opening — must be within 44 inches of the floor. This one surprises people: a window can be big enough but mounted too high, and it still fails. In basements with deep foundation walls, the original small windows often sit 5 or 6 feet up. A code-compliant install cuts the opening lower, which usually means a deeper window well outside. That is normal, and it is why the well needs a ladder.
The Well Has Minimums Too
The window well must be at least 9 square feet in area and project at least 36 inches from the wall — room for a person to open the window fully and climb out. Wells deeper than 44 inches need a fixed ladder or steps. A window that meets every size rule but opens into a shallow, ladderless pit is not a code-compliant escape.
How We Size Your Window
During the free visit we measure the room, the wall, and the outside grade, then pick the smallest window that clears every minimum with margin — because inspectors measure too. We would rather give you an opening that passes with room to spare than one that squeaks by. That is part of every installation we do.
Call (301) 679-9193 or send the form for a free written estimate.