Monday, March 26, 2012
Spray foam insulation? JUST SAY NO!
There has been an interesting question I've been hearing from more than one customer: "We want our new vinyl windows to be insulated with spray foam insulation. Could you do that for us?"
My answer, as much as I hate to say this word to any customer, is sometimes "NO".
Now, before everyone who has been reading up about ways to "build green" beats me up with their geothermal heaters, let me explain from the informed perspective of a contractor who has installed THOUSANDS of windows.
There are many styles, shapes and varieties of windows. Vinyl windows, whether they are replacement or new construction, are different from conventional wooden windows in a few ways. One of the most obvious is that the jamb of a vinyl window isn't as rigid. What that translates to is, in a standard double-hung, vinyl window with both sashes operable (meaning they both go up and down) the jambs will have a tendancy to bow outward away from the sashes. They don't bow inward becuase the sashes prevent that when they are closed and locked. To this end, most manufacturers equip their windows with what is known as a "jamb set screw".
The purpose of a set screw is to put pressure from the window jamb out against the framing of the rough opening to keep the jamb from spreading outward. Typically over a few seasons, the windows will expand and contract with temperature as vinyl is known to do. These screws are meant to be accessible so that adjustments may be made to the window over time to ensure continued, proper function. Now here's the part some installers don't like to admit to: Spray foam insulation (polyurethane foam) destroys the ability to adjust a vinyl window and completely disables the function of the manufacturers jamb set screw. Not only that, but due to the nature of the foam's expansion qualities (it more than quadruples in size), it can actually press the jamb inward towards the sashes and after it dries.... Presto! your window is permanently locked in maladjusted position with the sashes binding against the jamb as you try to raise and lower them.
The reason the we at Focalpoint Renovations will only use fiberglass or non-rigid insulation is simple, we'd like the windows we install to actually perform the way they were intended to. A window installed and insulated properly WITHOUT spray foam insulation will readily pass LEED green air leak tests. In fact, using a spray foam insulation in some cases actually VOIDS the manufacturers warranty!
In our quest to make our homes as efficient and draft free as possible, sometimes we need to make sure the cure isn't worse than the disease. Polyurethane spray foam insulation has many usefull applications in the world of construction but, for vinyl window insulation? JUST SAY NO.