Egress window code is a requirement intended to ensure a person can escape a building through a window in an emergency. Most codes also require windows to be large enough for a firefighter with his pack on to enter through them. The minimum standards of egress window sizes are uniformly defined by building code requirements of the 2015 International Residential Code (IRC). The key concerns to conform with building code include: A minimum clear opening width must be at least 20" A minimum clear opening height must be at least 24" A minimum clear opening size must be at least 5.7 square feet The sills on egress windows can be no higher than 44 inches from the finished floor. This diagram illustrates these egress window minimum size and code requirements: The following code requirements for both natural light and ventilation in basement settings may be required, check with your local jurisdiction: For natural light, the glass area, in square feet, must be at least 8% of the total floor area that the egress window is servicing. For example: If you had an egress window that has a glass area of 48" x 48" or 16 square feet, that would service an area up to 200 square feet. 16 square feet = 8% of 200 square feet. If the basement area you wish to have serviced by an egress window is larger than this 8% rule allows, you can use multiple egress windows to achieve the minimum 8% of glass area for natural light. For ventilation, the window's clear open area, in square feet, must be at least 4% of the total floor area that the egress window is servicing. For example: if you had an egress window that has a clear opening of 24" x 48" or 8 square feet. That would be able to service an area no greater than 200 square feet. 8 square feet = 4% of 200 square feet. If the basement area you wish to have serviced by an egress window is larger than this 4% rule allows, you can use multiple egress windows to achieve the minimum 4% of clear opening size for ventilation.