NOTE: This is an old article. An updated post can be found here – Complete Guide to Making Your Own Window Sill
WOOD SELECTION & CUTTING
You can use any type of wood, as long as they are kiln dried with the exception of pressure treated (PT) wood. Although PT lumber provides superior resistance to rot, it also gives off volatile organic compound (VOC) gas. Couple that with part of the sill being inside, I do not want to take a chance that my family will breath in VOC gas . The wood must also be absolutely dry so that a primer + paint will properly adhere to the sill’s surface. Although bit pricey, I chose cedar (fig.7.1) because of its natural resistance to rot (and they smell good!)
Step 1 – Because the width of a sill is rather narrow while working with a circular saw (not a problem if you are using a table saw), I purchased a 6 ft long piece so that I can secure the piece with deckmate screws to my workbench. I planned to cut off the ends with screw holes at the end of the project.
Step 2 – To cut the nose angle, I adjusted the angle on my circular saw that will yield a 10 degree angle (fig.7.4).
Step 3 – To cut the rear angle, I adjusted the angle on my circular saw that will yield a 15 degree angle (fig.7.4).
Step 4 – A true dimension for a 2×6 lumber is 1.5″ x 5.5″. The height of the sample sill was 1″ 5/16″ (fig.7.5) so you can either remove 3/16″ via wood planer or leave it as is. Since I did not own a planer and the 3/16″ height is relatively negligible, I chose not to remove it.
Step 5 – The bottom profile on my sample sill had 4 grooves or channels to make prevent water from wicking up (fig.7.2). To replicate all of these profiles, you would need a router with various router bits. Since I only had a “dovetail” router bit, I chose to carve out this profile near the nose and not bother with the other ones.
Step 6 – To prevent water from wicking up from the top side of sill, my sample sill had a 3/4″ wide by 1/4″ deep “indentation” (fig.7.5). To replicate this indentation, I simply set my circular saw to 1/4″ depth and scored the length. One tip was to clamp down a metal ruler to use it as a router guide. I then used a chisel to knock out the high points and used a sander to smooth it out.
By the way, if you print these scaled drawings, you need to make sure that they are printed in actual size. If you don’t know how to setup your printer to do that, read this article