Bill Robinson: Now we’re going to install the window. The first step is to apply a bead of compatible sealant to the backside of the mounting flange.

Bill applies the bead of caulk over the pre-punched mounting holes in the flange. When he installs the window, squeeze-out from this tells him that the flange is sealed against the building all the way around. He applies the caulk along the top and down the sides, but he leaves it off the bottom flange so that if any water gets in, it will have a place to get out. That’s what the sill pan is for.

Bill: I have the sealant on the backside of the mounting flange. We’re ready to set the window in place and center it. No I’m going to put a fastener in the upper right-hand corner to hold it while I check for plumb, level, and square. Because I set the sill level and set the window on top of it, I only need to check for plumb and square. Measure across from diagonal corners in both directions. If the measurement is within 1/8-in. you’re all set. Go ahead and set another fastener in the opposite corner. with the second screw in, check for diagonals one more time.

Before installing the rest of the fasteners, I’ll go inside and make sure the window functions properly. It opens fine, so now I’ll continue installing the rest of the fasteners to the manufacturers specifications. I’m using a truss-head screw because is has a nice flat bottom and a low profile.

That’s it. It’s in. all we need to do now is flash it, install the casing on the outside, air-seal it, and we’re done.