Adding a bedroom to a finished or partially finished basement is one of the most common scope requests KCC receives — and one of the most frequently misunderstood from a code perspective. Many Twin Cities homeowners list their basement as having a 'bedroom' when it doesn't meet egress requirements. When it comes time to renovate or sell, that distinction matters significantly.
Minnesota's egress window code for below-grade sleeping rooms is specific, and the requirements affect both the window and the window well. Here's what the code actually requires and what changes when you add a legal bedroom.
Minnesota Egress Window Code: The Numbers
The following are the Minnesota State Building Code requirements for egress windows in below-grade sleeping rooms. All dimensions refer to net clear opening — the actual opening with the window fully open, not the rough opening or frame size:
- Minimum net clear opening area: 5.7 square feet. This is the product of the clear width and clear height when the window is fully open.
- Minimum clear height: 24 inches. This is the vertical dimension of the opening.
- Minimum clear width: 20 inches. This is the horizontal dimension of the opening.
- Maximum sill height from floor: 44 inches. The window sill cannot be more than 44 inches above the finished floor — so occupants can exit without a stool or chair.
- Window well requirements: if the window is below grade, a window well is required. The well must have a minimum horizontal projection of 36 inches from the window face and a minimum width of 36 inches.
What Changes When You Add a Legal Bedroom
Making a basement room legally habitable as a sleeping room triggers a chain of requirements beyond the window itself:
- Permit: adding a bedroom requires a permit. The permit triggers a full review of the basement finish condition — including ceiling height, smoke detector locations, electrical, and HVAC.
- Window enlargement: most existing basement windows do not meet egress requirements. Enlarging a window in a poured concrete or block foundation requires cutting the foundation — typically $1,500–$3,500 per window depending on wall type and access.
- Window well installation: if a well doesn't exist or doesn't meet the 36-inch projection requirement, it must be installed or enlarged. Prefabricated galvanized or polycarbonate wells are typically $300–$600 installed; concrete wells run higher.
- Window well cover requirement: covers are not code-required in Minnesota but are strongly recommended. Wells without covers collect water and debris and can become a hazard for young children.
- CO detector: a CO detector is required within 10 feet of any sleeping room. If the basement doesn't have one, it must be added.
KCC handles basement bedroom additions throughout the West Metro, including foundation window cuts, well installation, and the full permit process in Hennepin and Carver County. If you're planning to add a bedroom to a basement in Plymouth, Minnetonka, or Eden Prairie, request a consultation to understand what the scope actually involves.