When you need an egress window
Under the 2018 International Residential Code (section R310), which the City of Knoxville references, every basement and every sleeping room needs at least one emergency escape and rescue opening. Basement bedrooms each need their own. Finishing a basement into living space, or adding a bedroom, is the usual trigger.
The size rules
| Requirement | 2018 IRC R310 |
|---|---|
| Net clear opening | 5.7 sq ft (5.0 sq ft at grade floor) |
| Minimum clear height | 24 inches |
| Minimum clear width | 20 inches |
| Maximum sill height | 44 inches above the floor |
| Window well area | At least 9 sq ft, 36 inches in each direction |
| Ladder or steps | Required when the well is deeper than 44 inches |
Casements and large sliders meet these numbers more easily than double-hungs, because they open nearly their full size. See casement windows.
Replacing a bedroom window above grade
If you are only swapping an existing bedroom window, the 2018 IRC (R310.2.5) lets the new window skip current size and sill rules if it is the manufacturer's largest standard size that fits the opening and is the same operating style, or a style with equal or greater clear opening. That keeps most like-for-like replacements simple.
Cutting a new opening in a foundation
A new basement egress opening is a structural job: digging the well, cutting the wall, installing a header or lintel, setting the window, then draining and finishing the well.
- Block vs. poured walls. Concrete block can be removed course by course; poured concrete needs a diamond-blade saw and costs more.
- Digging in East Tennessee. Knoxville sits in the Ridge-and-Valley Appalachians, and buried rock can turn up where a well is dug. Ask how the quote handles it if the excavator hits rock.
- Drainage. With just under 52 inches of rain a year, a well needs a drain tied to the footing drain or a gravel sump, and a cover helps keep leaves and rain out.
- Permits. Cutting a foundation opening needs a building permit from the City of Knoxville, Knox County, or your town's codes office.
Cost
National cost guides put a full basement egress installation at about $2,700 to $5,900, averaging roughly $4,200, including the window, well, excavation and cutting. One component breakdown lists the window at $800 to $2,000, the well at $400 to $1,200, excavation and drainage at $800 to $2,000, and cutting with lintel at $600 to $1,500. These are national figures; rock and access change local quotes. See the cost guide.
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