Let me start off by saying that as well as being a busy and highly qualified Home Inspector, I am also a Certified Window Installer and the Installation Inspector for the Siding and Window Dealers Association of Canada (SAWDAC) in the Calgary area. We call it the Window Wise Program. The installation procedure that we teach installers is consistent with the CSA Standard A440 which is referenced in the Alberta Building Code. I inspect a percentage of the installations, to make sure that the Standard is being adhered to.

Wood is a very stable material, and that is what most windows used to be made of. Wood windows didn’t tend to distort much. Today, however, most windows are made of vinyl. Vinyl is not so stable. When heated and cooled, vinyl expands and contracts and it will distort. Leave a piece of vinyl in the sun and see what happens, remember the old vinyl records. Because of this, it is important to hold the windows firmly in place, but not too firmly. The vinyl must be allowed to expand and contract. We have to control this movement, or the window will distort. We want to allow movement and encourage the vinyl to return to its original shape and position.

If we were to put solid blocking in all the corners, or make the window to fit the hole perfectly preventing movement in that direction, we would create a problem. The vinyl will find a way to expand. It will bow or twist; it could even break the glass. The opposite would also create a problem. Many installations are made without any shims to support or restrain the window. For many years now windows have been installed by attaching the nailing fin only. This method has been found to be inadequate and in many cases harmful to the window. The nailing fin is a thin piece of vinyl that projects outward on all four sides of the window. Nails are driven through the fin into the wall framing around the window. If the hole is a bit large, or the rough opening is not square the framing is not behind the fin everywhere. If the fin is damaged in transport, nailing it is useless. This technique holds the window in place, temporarily. There is no support. Sometimes a couple of scrap blocks are used to support the window off the rough sill. They are usually incorrectly placed, though and create further distortion. Unsupported and unrestrained, the windows will distort based on the loads and pressure placed upon them. If they are supported on the corners, they will sag in the middle. If they are supported only in the middle they will sag in the corners. Sometimes the bottom jamb (base of the window) looks like a roller coaster.

If the window is not level and square five years, or even one year after installation, it wasn’t installed correctly. I have inspected many installations, and most of them are wrong. Some of them, especially casements, have become problematic within the first year.

Mike Lancop, RHI

High River, Alberta