Minimum Egress Window Size in Colorado: What the Code Actually Requires

If you're finishing a basement bedroom in the Denver metro, the egress window is the one detail you can't get wrong. Colorado doesn't publish its own egress window dimensions — the state and most Front Range jurisdictions adopt the International Residential Code (IRC), which sets the numbers. Here's exactly what the code requires, and what those numbers mean for your project.

The Egress Window Minimum Size Colorado Adopts (IRC R310)

Under the IRC, an egress window must meet all of the following minimums. Failing any one of them means the window doesn't count as an emergency escape and rescue opening:

• Minimum net clear opening area: 5.7 square feet (5.0 sq ft is allowed only for grade-floor windows)
• Minimum net clear opening height: 24 inches
• Minimum net clear opening width: 20 inches
• Maximum sill height: 44 inches from the finished floor

"Net clear" is the key phrase. It's the actual unobstructed opening you get once the window sash, frame, and any hardware are accounted for — not the rough opening in the wall. A window listed as 32" x 48" does not automatically deliver a 5.7 sq ft clear opening. This is the single most common mistake homeowners make when shopping for windows online.

One more requirement people miss: if the window has a sill height more than 44 inches above the floor, it doesn't qualify at all — no exceptions for "it's close." A permanently attached ladder or step is sometimes permitted by local amendments, but you should confirm with your building department before counting on it.

What 5.7 Square Feet Actually Looks Like

Because the minimums apply simultaneously, a lot of standard basement window sizes fall short. For example:

• A 24" x 36" clear opening is only 6.0 sq ft but fails the width test at 20" — it passes width, but check height: 24" height and 36" width gives 6.0 sq ft, so it works. The reverse orientation usually fails.
• A 20" x 40" clear opening hits 5.6 sq ft — just under the 5.7 requirement.
• A 30" x 30" clear opening gives 6.25 sq ft and passes both dimensions comfortably.

In practice, most Denver-area egress installations land in the 30" x 48" to 36" x 48" range for a single casement or slider, which reliably clears 5.7 sq ft with room to spare. A casement window typically provides more usable clear area than a single-hung or double-hung of the same nominal size, because the sash doesn't eat into the opening.

Denver and Front Range Code Context

Colorado has no statewide residential building code, so adoption happens at the local level. Denver, Aurora, Lakewood, Arvada, Centennial, and most Front Range cities currently enforce a recent edition of the IRC, and the egress dimensions above are consistent across them. A few practical local notes:

• Permits are required. Adding a basement bedroom or cutting a new opening in a foundation wall triggers a building permit in every metro jurisdiction. The inspection typically covers both the window specs and the window well.
• Window well requirements. If the window is below grade, the well must provide at least 9 sq ft of horizontal area and a minimum 36" horizontal projection. Wells deeper than 44" need a permanently affixed ladder or steps.
• Soil conditions. Much of the Denver metro sits on expansive clay and, in areas like Highlands Ranch and Parker, significant bentonite. That soil swells and shifts with moisture, which is why window well installation here needs proper drainage and backfill detailing — not just a plastic liner dropped into a hole.
• Front Range weather. Hail, freeze-thaw cycles, and heavy spring snow loads make well covers, drainage gravel, and properly sealed flashing worth doing right the first time.

Getting the Specs Right the First Time

Because the code tests clear opening, not nominal size, the safest path is to have the opening measured and specified before you buy anything. A contractor who does this daily can tell you in a few minutes whether your existing foundation wall can accommodate a compliant window, or whether the opening needs to be enlarged with concrete cutting.

At Affordable Egress Co., we've handled egress window installation, window wells, basement bedroom conversions, and concrete cutting across Denver and the Front Range since 1999. Most of our installs are completed in a single day, including the cut, the well, and the finish work — which means less disruption to your household and a faster path to inspection. We also handle the permit paperwork and know what each metro jurisdiction's inspectors look for.

If you're planning a basement bedroom or just want to know whether your current windows are code-compliant, start with a free estimate. We'll measure the actual clear opening, confirm the requirements for your specific city, and give you a straight answer on what's needed — no guesswork, no upselling.