Unwanted Surprises with House Window Installation in Old Homes

Plopping new windows into your house is usually a pretty straightforward process. Whether you are dealing with wood frames, vinyl or fiberglass, the actual process is similar, and you might say the instructions are as clear as glass.

But if you are replacing windows in an ancient home, you may encounter some pitfalls that fog up the simple process.

New Windows, not Replacements

We're talking here about new, full-frame windows, not the replacement type where you put the glass insert into the old framing. If your old frames have rotted or are otherwise falling apart, then you need to replace them with full frame windows.

House Window Installation - Unsettled Settling

Through the decades, your old house may have settled so the rough framing for the window no longer is square. Most importantly, the bottom plate of the framing may not be level: you may have a clue to this problem if the old window did not open and shut smoothly.

Setting the window onto unlevel framing can lead to distorting the square of the new window so it doesn't open or close properly. You will need to shim the window level, making sure there is space between the window and framing on all sides, so that heat expansion or further shifting does not bind the window.

If the framing is significantly out of whack, you would be wise to investigate the cause. You may have foundation problems that must be fixed, or you may have significant rot that has allowed the structure to sag.

Rotten Luck

Another pitfall of house window installation: When you pop out the old window, you may find rotten wood. Somewhere your old home's water-protection system has failed. If the leak has not previously been repaired, then obviously you need to deal with it. And you have to tear into the wall to see how far the water damage has traveled.

One More Woe

Your rough framing may be nonstandard measurements, not obvious without careful measuring. Remove the trim from the window so you have access to the rough framing for accurate measurements before ordering your glass--your rough framing should be 1/2" to 1" larger than the window size. (Note: windows are designated by their rough-frame size: a 4'x6' window, for instance, is actually half an inch smaller in both directions, but the rough-framing for it is 4'x6'.)

Old houses are particularly susceptible to unwanted surprises, and house window installation opens up some of the rough framing where those surprises are apt to dwell.