How to make a new window stool
Classic window trim includes a piece of trim that sits on top of the sill. Called the window stool, it's the place our grandparents used to set the pie to cool. We'll show you how to add this traditional feature to your windows, but you're on your own for the pie!
Our photos show how to make a simple stool for older-style, double-hung windows. The stool board is just a 1x4 (3/4 in. x 3-1/2 in.) that you cut to fit and then round the edges with a router. Because the lower sash of these older-style windows is set back on the sill, the ends of the stool board must be notched to fit as shown in Photo 4.
If you have newer windows, including casement (crank-out) windows, the job is easier. They have a factory-made extension piece that makes them fit flush with the drywall, so you only need a straight piece of wood for the stool. It's not necessary to notch the ends.
Keep in mind that the stool shown in Fig. A is for larger-scale casing that's 3/4 in. thick and 4 in. wide. For modern, slimmer casing that's about 7/16 in. thick and 2-1/4 in. wide, the stool should project from the wall only about 2-1/2 in.
Cutaway diagram of a typical double-hung window with window stool
Use this cutaway diagram to visualize how you'll install the window spool. Notice that the window stool extends underneath the casing and jamb pieces; you'll have to remove them before marking, cutting and installing the new window stool.