Basement Window Sill Replacement

Posted by Steve Cuddihy On Monday, October 24, 2016 0 comments
So with the Garage Painting Project completed, we had some trim work around the house windows that needed a quick paint job. Wifey noticed one of the windows, ummm, didn't want any paint on it. Essentially, it was in rough shape the last time we painted it. This time around, it started to crumble. My first thought was to replace the entire window, as that is what we'd like to do with all of the house windows, just not right now. After some thought, I decided I would tackle replacing the rotted window sill myself.

As you can see, there's just not much left of it on the outside of the house. Most of the remaining frame is still in great condition. The bottom of the two side pieces where the decaying wood is really the only other questionable portion. Time to find my Sawzall and cut out the rotted sill.

There it is, my Milwaukee Sawzall, ready to cut out the bad board. First I made two cuts, but left one to two inches of wood. There were no nails in the main part of the sill, but I did have staples holding the window frame together.

Next I used a 1 inch chisels and started breaking out the remainder of the sill piece by piece. The staples were about an inch long, so I had a tough time breaking these free. Eventually they came out and the old board was completely gone.

I purchased a 2" x 6" AC2 Green Treated board from Menards for $3.39 and I was ready to recreate the new sill plate.

So after taking my window frame measurements, I needed to figure out how to cut an angle on the front of the sill as the board will sit at a bit of an angle once it is installed. So I used the back side of the original sill, as it also had an angled cut.

The remaining piece was so small, there just wasn't enough to get a true angle. I couldn't quite match it up on my test cuts, so decided to just take a guess and be happy with it.

So the width of the window was 36 inches, however the inside frame was 34.5 inches. Or something close to that. With the front and rear of the new sill angled, I made the cuts on the side of the board.

The YouTube video I found, it said to spray paint the sill with a water resistant primer, which I was eager to do.  After spraying the new board, I then recalled I needed to make more cuts to the front and sides of the new sill.

I had to break out the Shop Smith at this point to make these next cuts. I needed to match up the angle of the new sill in order to keep the cuts correct.

I just used a single blade and made several runs through, then chiseled and sanded for the final finish.

Made the cuts on the sides, cleaned it up and spray painted the board once again, so it hopefully slides right in place. Well, you know it will be a bit of a fight.

And this is the final look of the board. I did have a bit of a struggle with the board. First, I had removed a 1 1/4 inch board and replaced it with a 1.5 inch board. I knew I would have to cut some of the frame out, however since some of this wood that contacted the old sill plate was rotting, it wasn't a big deal to raise the plate by a quarter inch.

I did have to do a bit more sanding to get the board in place, but eventually I was able to get the replacement sill in place. The one item I overlooked was the aluminum storm and screen frame was now a but to large for the smaller opening. I fixed this by cutting off a small portion of the frame. I had a full functioning window at this point.

Lastly, I used some wood filler in the quarter inch gap on the left side of the sill to fill in the last of the rotted wood. I was debating between replacing the entire strip of wood or just the last few inches of the wood, but my father suggested to try the wood filler. In the end it was a quicker fix and is covered up quite well with the last coat of paint.

Here is the finished project. I will have to replace the glazing another time as the weather is starting to turn for the season and there are a couple of pressing projects that need attention yet before the snow flies.

Oh yeah, let's put the storm window back on to complete this project.

Before and After