## 27 Jan How Much Is Enough?

Goal: You will be able to calculate the linear feet of window trim needed for any dimension window.

Interior window trim (casing) is a molding that is nailed to the finished window frame to give the window a “finished” look. The trim is located on the inside of the home around the perimeter of the window frame and is often cut at a 45º angle. See picture. You can think of it as a picture frame around the window. The same idea is also used around doors.

Problem 1:

Your window frame (inside edge) is 38” wide by 54”. There is to be a 3/16” reveal on all edges. Your corners are mitered at 45º. The trim (casing) is 2 1/4” wide. How many inches of trim do you need? You can ignore saw blade width but do need to consider casing profile.

Problem 2:

Problem 2 is a generalization of problem 1. What is a formula (shortcut) for finding the length of trim needed if the window size is “w” inches wide and “h” high with a trim width of “t”? Again, assume you have a casing profile to consider.

Teacher Notes:

Students may need to research terms such as reveal, casing, and casing profile unless you provide a demo. You will need to decide if you need to give hints regarding 45-45-90 special right triangles. You can extend this to building a octagonal frame using 30-60-90 special triangles. Trim carpenters know the rule by heart but do not call it a “formula”.

Geometry in Construction