How to Understand Wood Window Sizes

When you receive a set of architectural plans or a group of shop drawings from your builder or architect it can be terribly confusing. Window sizes are difficult to comprehend. There are random numbers and abbreviations that do not seem to make much sense. They do guarantee that you will get the proper windows ordered for your project. With a little practice and a cheat sheet you will get the hang of how wood windows are listed in architectural plans and specifications.


Step 1

Read a window size listed on a set of architectural drawings. It will look similar to "3050," which specifics the window's dimensions. The numbers represent a window that is 3-feet 0-inches wide by 5-foot 0-inches tall. The first digit is in feet and the second digit is the inches that a window is wide. The third digit is in feet and the fourth digit is the inches that the window is tall.

Step 2

The "3050" is the actual size of the window unit. That is not the same thing as a "RO" known as the rough opening. The rough opening will be generally 1 to 1-1/2-inch larger than the actual window size. The framers use the rough opening to make an opening that is large enough to accept the window and with room enough to shim and level the window within the rough opening.

Step 3

Determine the egress of a window. The window will be listed as an egress or a non egress window. The term egress is used by code officials. The building code states what the minimum window size is to allow a person to escape the living space through the egress window in case of an emergency. The building code varies from state to state depending on what version of the building code is in use.

Step 4

Determine the window grids or "lites." This window lite pattern will be entered in the window schedule as "3x5 SDL". The 3x5 means that the window is divided into three vertical columns and five horizontal columns. So the window will have 15 separate small windows or "lites" within the one window frame. The term SDL stands for simulated divided lite. This means that there is only one large glass pane divided into a mullion grid that simulates the appearance of many different pieces of glass.