Retrofitting a new window isn’t always easy, because you want the new window to integrate seamlessly into the existing siding. So before he makes any cuts, Bill builds the casing for the new window. The trick with the casing is that you want to add 1/4-in. to the inside dimension for a caulking joint between the casing and the new window. This helps with expansion and contraction. He also uses pocket screws and construction adhesive for strong water-resistant joinery. The reason that he builds the casing first is so that he’ll have an accurate template to measure his cuts from. Next, he builds a cutting guide out of 1/2-in. plywood. The cutting guide, also known as a shooting board, guides the saw over the uneven siding. Bill makes sure to cut on both sides of the guide’s fence so the board can be used form either direction. Bill Robinson: What I’ve done here is set up my crosshair laser level to give me centerline on this window. What I’m going to do now is take my measurements off the center of this line here and extend them out either direction. That’s going to give me the marks I need to make to set up my shoot board to make the cuts and remove the siding. This casing is 58 3/8-in. wide. I’m going to leave a little room, so I’ll mark to cut the opening 58 1/2-in. wide. That’s 29 1/4-in. to the left and right from my center mark. Once I have my shoot board set up, I’m ready to make my cut. The next thing I have to do is set the depth of my cut. It’s better to cut to shallow than too deep so i don’t do any damage to housewrap or sheathing underneath. Now I’m…