Install Your Own Windows
(Page 3 of 4)
December 2005/January 2006
By Steve Maxwell
At this stage, you have a nice, new replacement window in place, though you can still see daylight shining in through gaps around the perimeter. This is where expanding polyurethane foam can help; you want to use a low-expansion formulation to seal the gaps. Make sure you do a good job sealing all the openings because failure to do so could compromise your new window’s overall energy efficiency. As added insurance against the nightmare of a window frame bowed by pressure from the expanding foam, cut wood braces that fit within the window frame and stay there by friction, positioning them against the inward pressure of the expanding foam (see illustration). You’ll be fine if you place braces between wedge locations.
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Before you spray the foam, weatherproof the outside joint around the perimeter of the new window. The best option is to stuff lengths of a cylindrical foam packing material called “backer rod” into the gap between window and frame. Choose backer rod with a diameter that’s twice as wide as the gap, and then push it in to a depth that’s equal to the gap width. This creates a square groove that’s perfect for caulking. One length of masking tape laid down on each side of the outside joint is the easiest way to achieve neat caulking results. Pump the caulking in, smooth it with your fingertip and then immediately peel off the tape.
Next, inject foam as deeply as you can within the gap along all interior edges and don’t worry about excess ooze. Just let the foam completely harden (at least six hours) and then trim off the excess with a hacksaw blade. This kind of blade is flexible enough that you can bend it flush with the surface as you cut, giving you exceptionally clean results.
The final interior step is the installation of wooden trim to cover the foamed gap and joints between the replacement window and the old window frame — this way, you’ll get some practice with the miter joints. Standard quarter-round wood trim is perfect for this job, but it’s not the only choice. You can use any trim that fits within the 90-degree corner formed where the replacement window meets the old jamb. If you’re using hardwood, pre-drill holes for the finishing nails to prevent splits.
Putting Windows in New Buildings
The process of installing windows in new buildings is similar to replacement work, but with two key differences. Most modern window designs include an exterior mounting flange that reduces or eliminates the need for wedges. Also, you’ll need to pay much more attention to weatherproofing windows in new construction than with replacement work. There’s more to it than just applying caulk; new windows need to be incorporated into the exterior wall treatment of the building as it is raised.
