Egress Windows: What a Legal Basement Bedroom or ADU Actually Needs

A basement room is not a bedroom until someone can climb out of it in a fire. That is what an egress window is, and it is the most common thing standing between a finished basement and a legal bedroom or rentable unit.

Expect $4,000–$9,000 per opening to cut one into a poured foundation in the Seattle area. On a daylight basement it can be close to free. Here is the difference.

What the code is actually asking for

Not a window — a way out. The residential code sets a minimum clear opening area, a minimum clear width and height, and a maximum sill height above the floor, so that an adult can get through and a firefighter can get in. Below grade, that opening needs a well large enough to stand in, with a permanent ladder or steps if it is deep. Every sleeping room needs one, and a separate dwelling needs one from each bedroom.

Jurisdictions adopt the code with local amendments and inspectors measure to the inch, so we confirm the numbers that apply to your parcel rather than quoting a universal figure here.

Why sloped lots win

On a flat lot the basement wall is fully buried. Meeting egress means excavating a well, cutting a structural opening in the foundation, installing a header, waterproofing the cut, draining the well, and then fitting the window. That is the $4,000–$9,000.

On a daylight basement — the hillside stock through Bothell, Mukilteo, Edmonds and north Seattle — one wall is already above grade. A full-size window there is a framing job, not an excavation, and often an existing opening only needs enlarging. It is the single biggest reason daylight-basement ADUs cost less than their flat-lot equivalents.

What the price is made of

• Concrete cutting. Sawing a poured or block foundation and removing the slug. Rebar, thickness and access move this.
• Structure. A header to carry the wall above the new opening, engineered where the span or load demands.
• The well and drainage. An excavated well with a retaining liner, gravel base and a drain tied to the footing drain or daylight. Skip the drain and you have built a pond against your foundation.
• Waterproofing the cut. The fresh edge of the foundation is the most vulnerable point on the wall in this climate.
• The window. A casement or slider sized to achieve the clear opening — see window replacement cost for frame options.
• Permit and inspection. Not optional, because the whole point is a room that is legally a bedroom.

Where it fits in the bigger project

Egress is one of four things that separate a finished basement from a legal dwelling, alongside ceiling height, an independent entrance and fire separation. If the goal is a rental or an in-law unit, plan all four together — the ADU explainer covers the rest — because an egress window in a room that fails on headroom has not bought you anything.

It is also worth doing even when the goal is only a bedroom for your own household: a basement bedroom that cannot be counted at sale is square footage you paid to finish and cannot sell.

Find out what your wall needs

Three measurements and a look at grade decide it. We build ADUs and lower-level conversions across Snohomish and King County, and the free estimate will tell you whether yours is a window or an excavation.

Get a basement assessed →