Egress Windows Prices : Egress Window Size Requirements
Egress Window Size Requirements
Our egress window size requirements provides building code size charts for many of the most popular styles of basement egress windows. The four most popular basement egress window options include casements, horizontal sliders, double hungs and single hung windows.
International building code requires that a basement egress have a minimum net clear opening of 5.7 square feet. A net clear opening is the measure of the usable opening space when the window is fully opened. In other words, it is the amount of clear, open space through which a person can crawl out of in case of an emergency. It is NOT the size of the window opening itself, which will always be larger than the actual space through which an individual could climb out in case of an emergency.
Casement Egress Window Sizes
Casement windows are one of the most popular options when it comes to a basement egress window. A casement window is hinged on one side and, when opened, provides a much larger net clear opening than with any other window style (see the picture below to see why). This means that a casement does not have to be nearly as large as other window styles to meet the minimum building code requirements.
According to the IBC, a casement must be at least 24 inches in height and 20 inches in width to meet egress requirements. However, a casement that is 24 inches in height and 20 inches in width does not meet the required 5.7 ft.² clear opening. (24 x 20 equals 480 divided by 144 equals 3.3).
It is unclear why building code would provide minimum height and width requirements if they do not meet the net clear area, however it is what it is, as they say. For consumers, the number you really need to pay attention to is net clear area of 5.7 ft.². So for a casement window to meet requirement, it would have to be, for instance 24" by 34", which equals 5.8 square feet of net clear opening.
Sliding Egress Window Sizes
Sliding windows are the second most popular basement egress option behind casements. Horizontal sliding windows open from side to side and are typically longer horizontally than vertically. Horizontal sliders have a smaller percentage of net clear opening compared to the total size of the window opening than a casement. The result is a larger window requirement to meet the building codes 5.7 square feet.
Sliders must be a minimum of 4' wide by 4' in height to meet code requirement. However, most sliders only allow for roughly 45 percent net clear opening compare to the total size of the window. In the case of the 4' by 4' slider, the net clear opening is equal to 3.2, which is obviously significantly smaller than the required opening.
Double Hung Egress Window Sizes
Double hung windows are also a popular basement egress window option. Double hungs are more vertical than horizontal in terms of their shape and have an upper and lower sash that can be opened independently of one another. Double hungs offer roughly the same net clear opening percentage (45 percent of the total size of the window) as a horizontal slider.
Building code requires at least a 3' wide and 5' tall double hung window, however the provided roughly 3 sq ft net clear opening, which is also significantly less than the required 5.7 sq ft.
Single Hung Egress Window Sizes
Single hung windows have a single lower sash that can be opened vertically in much the same way as the lower sash of a double hung window. Similarly to a double hung window, the single hung provides approximately 45% net clear opening compared to the total window size.
Building code requires a single hung up he 3 feet wide by 5 feet in height. Again, using the 45% this would provide approximately 3 ft.² of not clear opening, which is just over half of the required 5.7 not clear opening. This means that the single hung would have to be significantly larger in order to meet the building code.