Prep Window Opening
Bill Robinson, contractor and construction trainer: When preparing the rough opening, it’s important to look for damage, and moisture is the main culprit. To check for damage here, I’m going to use my chisel and stick it into the wood and pry on it. Look for the wood to splinter up like that. That means it is sound wood. If it crumbles, you have to replace it. The felt paper you can see here is sound—it’s actually solid behind. I didn’t cut it when I removed the siding, so I’m not going to worry too much about water getting behind there. The felt paper is in pretty good shape. The window opening is big enough to fit the window. And it’s plumb, level and square enough that I can make some adjustments when I install the window. So we’re good to go. [Narrator: Bill fills in missing gaps of sheathing around the rough opening. Then he vacuums all the dust and dirt so that he’ll have no trouble installing the rigid and self-adhesive flashings.] This is vinyl coil stock. It’s real thin, and what’s nice about it is that it pretty much won’t react with moisture or anything. I cut this in narrow strips and slide it behind the siding. Any water that might get inside the window opening will be forced to the outside. I work the coil stock down behind the siding carefully and use a little pry bar to pull the siding away from the felt paper so that I can get the vinyl coil stock behind there. It’s kind of a tight fit, but I need to get it in there. So, I’ve done the bottom with the vinyl coil stock. I’m going to do both sides but leave the top open so that the flashing tape will actually stick to the raw framing itself on the wall. Everything installed while you’re flashing should be installed shingle style, which means what’s at the bottom should be covered by what’s above it. Next, put in the self-adhesive flashing. The first piece will be here on the sill, overlapping the vinyl coil stock, and it will roll into the sill a little bit. Self-adhesive flashing has release paper on it. I’m going to position it where I want it to be with a little bit wrapping up at each end. Get it to stick, pull the release paper off, and keep it in a straight line. Readjust it as you go. If you take all the release paper off at one time, you’ll get it wrapped up into a sort of snowball or flashing ball. With the corner in, make cuts and fold it out along the face of the wall. Whenever you’re applying self-adhesive flashing, it’s critical to use a J-roller; that’s going to make it stick. Next, flash the corners. [Narrator: The flashing material is 6×6 flexible self-adhesive squares. Bill uses them to seal up the corners. They’re a little tricky to work with, but after he’s got them into position, he J-rolls them for a good seam. Next, he flashes the sides of the rough opening with more self-adhesive flashing material.] I have the side jambs flashed before I put the window in. Add a corner shield at the top for a little bit of extra insurance to keep water out of there. Now that the top corners are in, it’s time for the sill pan. The sill pan is especially important because it’s going to drain any moisture that gets inside the opening to the outside. The sill pan is pretty cool. On the back is self-adhesive flashing that sticks to the frame. There’s some foam in the back that won’t absorb moisture. That’s going to set into the inside of the window. Any water that gets inside will be forced to the outside—but here’s the cool part. This has some sort of wicking material that, when it faces outside, will drain water to the outside even if the sill is sloped backward, toward the inside of the house. [Narrator: To ensure the window and rough sill aren’t damaged by leaks, Bill wants pan flashing running from the inside of the sill, out and down the sheathing. The flashing isn’t quite wide enough, so he cuts strips from the sill material and layers them. Like everything else here, he starts at the bottom and works his way up, shingle style.] Now that the filler piece is in, I’m going to put in the sill pan piece itself. I’ve already cut it to length. Take off part of the release paper, pull it out of the way, set it down firm here, and pull the paper out slowly to keep it straight. With the sill pan in, it’s time to dry-fit the window. If the dry fit looks good, it’s time to take it out and do the permanent install.
Bill Robinson, contractor and construction trainer: Now that I’m ready to install the window, the first step is to apply a bead of compatible sealant to the back side of the mounting flange, or the nailing flange. [Narrator: Bill applies the caulking to the prepunched holes so that when he installs the window he’ll see squeeze-out. This tells him that the nailing flange is sealed against the building all the way around. He applies the caulking along the top and the sides, but he leaves it off the bottom flange so that if any water does get in, it will have a place to come out; that’s what the sill pan is for.] I have the sealant on the back side of the mounting flange. I can set the window in place and center it. I’m looking for squeeze-out, and it’s coming out the prepunched holes on the side. That means the window will have a good seal. It’s also coming out the top. Now I come down the right side, and I can see the sealant is coming out on the edge and out of the prepunched holes. Next, l put a fastener in the upper right-hand corner to position the window and check for plumb, level, and square. I set it snug. The window will actually stay in place now. So, that’s the first fastener in. The next thing I want to do is check for plumb, level, and square. In fact, because I leveled the sill in the first place and set the window right down on it, I don’t have to check for level again. But I do want to check for square, so I’m going to pull the diagonals. When the numbers are equal, or within an eighth of an inch or so, that’s good enough. What I do now is put in the second fastener, in the opposite corner. I want to snug it down, but not too tight, so that I don’t distort the flange. With the second fastener in, I check for diagonals one more time. The final thing I want to do is go inside and make sure the window functions properly. Since it opens fine, I’ll continue installing the rest of the fasteners according to the manufacturer’s instructions. I’m using truss-head screws, which have a nice flat bottom and a low profile, and will hold the window in place. These windows are molded together; you can see along the top here, the manufacturer says to put a screw between each one of these places where the tape is, to help hold the window in place. I’ll make sure they’re all bunched close together there. That’s it; the window is in. All I need to do now is flash it, install the casing on the outside, air-seal on the inside, and we’re done.
Install Flashing and Trim
Bill Robinson, contractor and construction trainer: Now that the window is installed, we’re ready to flash it. If you remember, I cut back the siding a little over 3 inches. I’m using 4-inch self-adhesive flashing. It’s actually a butyl tape. I use my cutting table here to get the dimensions. The table is 48 inches, and the tape wants to be 48 inches. Always start by removing some of the release paper so that once you get it into position, you can work it. Because this is an applied mounting flange, I need to be sure I roll the flashing tape up onto the window frame itself by about half an inch to make sure I have a watertight seal here. I use a Speed Square to push the tape up against the frame and overlap onto the frame itself. I cut this bit right here so that it lies flat; same thing at the bottom here. Repeat the process on the other side. Remember, everything gets a J-roller. [Narrator: Next, Bill cuts small pieces from the same flexible corner flashing to seal off the corners at the top of the window.] The first corner goes in here, and it wraps around. [Narrator: He also fashions a small piece to cover the joint where the two windows are molded together—another precaution.] Now the rigid flashing goes over the top of the window. I apply a bead of sealant to the back of it and center it. It will take any rain and deflect it away from the window. I put in a couple of fasteners up here to hold this in place and snug it up. The final step for flashing is to put the head flashing over the top. [Narrator: Because of the narrow space between the window and the soffit, Bill uses the shoot board to trim the top off the casing to fit the opening.] Now that I have the casing set up around the window, I use plastic shims to space it. The gap’s pretty good all around, so I fasten it in place. I’m using corrosion-resistant trim-head screws. The screw head is small so that it won’t leave a large dimple in the face of the material. [Narrator: Bill’s careful to set the screws far enough away from the window so that he doesn’t drive them through the mounting flange.] Remember, I left this intentional gap around the perimeter here. I put backer rod in that gap and then fill it with sealant. So, that’s the window caulk to the casing. Next I seal the window casing to the siding. I like to push the tube rather than pull it because I can see the sealant coming out the front of the nozzle on the caulk gun and I can tell I’m filling the joint much better that way. That finishes up the exterior install, and it’s watertight. Now I go inside to air-seal it. The best way to air-seal from the inside is with a polyurethane spray foam, one that’s good for use with windows. The main thing I’m trying to do here is stop air flow from the inside or the outside—not so much insulating as air-sealing. I want a nice even bead along the side and the top with spray foam. I don’t need to do that along the bottom because the sill pan has a foam gasket along the inside that will provide an air seal. If it didn’t have that, I’d have to spray-foam the bottom. That’s it. The window is watertight on the outside and air-sealed on the inside. It’s ready for drywall and trim, and then we’re done.