How To Shim, Level, and Fasten an Insert Replacement Window
Follow these techniques to ensure that your new window looks good and opens properly.
Remodeler, Mike Sloggatt: I’m going to prep this window so that when I get it into position I don’t have to struggle with it. I’ll set a couple of screws first so that when I put the window in there’s something to hold it together. Now that I’ve got the stops out, I’ll set the two top screws to hold the window in position while I do the final fit. Don’t put all the screws in. If you do, you won’t be able to open the sash; they’ll get in the way. I just have to put the sealant on the sill and we’ll be ready to set the window.
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Shim, level, and fasten the insert window (now playing)
I’m using a sealant made specifically for sealing windows and flanges of that nature. Once the sealant is applied, set the window into the opening and screw it in place.
Narrator: Mike starts the screws without driving them home, so he can shim the new window straight.
Mike Sloggatt: Our goal is to install the window properly, making sure all the reveals are good and everything is nice and even. We use shims and screws to position the window correctly. I also have to make sure the window sits even with the reveal so that the molding is nice and straight. At the bottom of the window, insert a shim between the window and the frame on one side and drive a screw; then do the other side. Even it up as best you can.
Next, set the depth of the window so that it’s right up against the stool. It should be the same on the top and the bottom. Use a sliding square as a depth gauge and set the depth at the bottom of the window so that you can duplicate it up at the top. Check the depth gauge at the top, insert a shim between the window and the frame, and screw it off. Do the same on the other side of the window so it is nice and even. I don’t set the screws in all the way because I might want to adjust the window a little bit here and there. But I definitely want to get the depth right.
Follow the same shimming and screwing process at the center of the window. Sometimes I use a pry bar to get the shims into position here. The shims are different thicknesses, so you can build them up as you need to, to get the right size to set the window properly. Double-check the depth at the center of the window and then run in the screw. Do the same on the other side.
At this point I’ve got the window roughed into position. It’s not perfect yet. Next, I go outside to make sure the sill is level. Use a bubble level. This one is a little off, so I’m glad I can reposition the shim and get the window just perfect. Go back inside and loosen one of the screws at the bottom of the window. Set the bubble level on the sill and insert a pry bar under the window so that you can slide in a shim under the sill. Check the level. If the sill is now level, drive in the screw.
I’ve got the sill level now. What I need to check is the plumb—making sure the window is nice and plumb on the sides and that there are no bows in the jamb. Take a 4-ft. level and tuck it right into the jamb. This one looks pretty good. All I have to do is snug up those screws into their final position. Moving the level to the other side of the window shows there’s a little bit of a belly in the jamb, so I have to move the center shim out an eighth of an inch or so. I loosen the screw, move the window over with another shim, get it nice and straight, and tighten it down. I just need to add about another eighth of an inch, so I set another shim right on top of the first shim. Double-checking it with the level shows that it’s good. Set the screw.
Now that the window is nice and straight, I just have to tighten all the screws and finish off the installation.
Narrator: Mike uses a chisel to cut the excess shim material so that the stops, which will be installed later, fit tight to the window frame. Now all that’s left to do is air seal the interior, trim out the exterior, and reapply the stops.