How to Make a Window Sill

Create New Framing Around the Window

We decided to have the windows replaced in the Rebel house rather than do it ourselves because we are a little pressed for time. The old window sills had been painted over way too many times and I felt it would be better to create new ones. The framing around the windows was drywall (old drywall, at that) and got torn up in the process of removing the drywall from the walls. Because I’ve done this in my own house, I’ll show you how to make a window sill and create new framing around a window.

I actually kind of like seeing everything come together and this is one job I don’t mind doing. Everything had been removed prior to the window installation so we were left with exposed studs and drywall edges. I like to use pine or spruce 1×6 lumber to create my window sills and framing. I start by measuring the area where the sill will rest. I then add 2-1/4″ to each side (a total of 4-1/2″) for the casing to rest on plus add a bit of a reveal at the edge.

To make the sills, cut the 1×6 to the total overall length. In my case, the total length was 49-1/4″. Then, I cut a 2-3/8″ x 4-1/2″ notch at each end with my jigsaw. This leaves the amount for the trim to rest on (as mentioned above) and makes the sill stick out 1″ from the wall. I like my sills to be a bit loose in the opening in case the studs aren’t set straight. Any gap between the edge of the sill and the stud will be covered by the framing.

Check for fit and level, shimming if necessary, then secure the sill using a few 1-1/4″ brad nails.

To create the framing, I measure each piece individually. Never assume the measurements will be the same. I promise you they won’t be but if they are, well, consider yourself lucky! I measure the distance from the inside of the window to the outside of the drywall, then rip boards to match this measurement. Then, I measure the distance on each side of the window from the sill to the header and cut pieces to fit. I secure them using 1-1/4″ brad nails.

Last, I measure the distance at the top between the side pieces and cut a piece of lumber to fit. I secure the final piece with 1-1/4″ brad nails. And of course I forgot to take a photo of this step… but you get the idea, right?

Now you know how to make a window sill and frame out a window! Super-easy, right? Of course!