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Window Seal Problems

What is the Window Seal?

The window “seal” refers to any part of the window installation that blocks out the exterior environment. Most often, the term “seal” is used for weatherization and energy efficiency applications, and usually refers to the sashes (in sliding windows) and lites (window panes).

Why Do Window Seals Fail?

Seals can sometimes fail due to:

  • Pressure building between the two panes of glass during hot days (referred to as “heat pumping”)
  • Contracting/shrinking in the colder months
  • Expansion and contraction of the sealant material itself

Seals fail most frequently on windows facing south or west due to longer exposure to the sun. Too much direct sunlight deteriorates the original sealing material more quickly than windows facing in other directions. When considering new windows, always opt for solid, long-term, transferable warranties (20-year warranties are preferred) because the windows will not only perform better for longer, but the transferable warranty also adds resale value.

Window Seal Restoration & Repair

Since replacement windows can be expensive, restoration or repair is the other option. There are two ways to repair a failed seal: Do it yourself or choose from a number of qualified window contractors, like those available through CalFinder. Blown seals around the window (also called the window gasket) will appear cracked or missing, but are not always so obvious. Occasionally, a seal will fail and go unnoticed until you find condensation between the panes of glass or, in the worst case scenario, unsightly mold will grow between the panes (the mold is sealed in however, so it poses less health risk than mold in walls).

Proper and/or upgraded pane spacers will also help prevent blown seals caused by heat pumping or cold weather shrinkage, because they allow the panes to breathe without building up pressure or window condensation.

Minor Fixes for Broken Window Seals

A quick fix for a blown seal is to add a bead of exterior silicon caulk, but it won’t look very good. The best method is to check if the gasket can be popped out without damaging the window. Use a wedge gasket as a replacement and be sure to get it in just right so the seals are made properly. If the gasket cannot be removed, you’ll need new panes for the window.

DIY Window Seal Repair

If you choose to fix a blown seal yourself, you’ll first have to find the source of the leak. Wait for an extra cold day and then feel all around the inside of the window. Pay special attention to any cold spots where the sash (sliding window) comes in contact with the sill or the other sash, as these are two places where the sealing properties of a window often fail. If you find a leak, silicon caulk is the best material but it cannot be painted over and it will seal a sliding window shut. For re-painting, use an acrylic/silicon caulk. Morlite also makes a putty-like weatherstripping that can at least cut the draft, if not re-seal the window. Check with your local hardware store. Another option is to use adhesive foam weatherstripping, which is also available at the hardware store. If you have trouble finding the leaks, a home energy audit could really save you the trouble of sleuthing them out. If the leak is entering where the panes slide across each other, it’s probably a job for the pros.

Seal Failure in Window Frames

The other common place for windows to fail (or to have never worked properly) is around the actual frame itself. Run your hand over the trim around the window and feel for cold spots. If you do feel some (or many), then it’s likely that the installer either skipped the step of insulating around the windows or the insulation has deteriorated. There are do-it-yourself fixes to this type of a failed seal using small bits of fiberglass insulation or even expanding spray foam, but you’ll need to remove the trim and carefully replace it, so basic carpentry skills are a must. If you choose expanding foam because you think it’ll be easy, please be careful, as the product is impossible to remove from fabrics, walls and everything else you didn’t want it on. It is certainly easier in the long run to use fiberglass bat insulation, but be careful not to compact it into the gap around the frame. Instead, allow the insulation to regain its original thickness as much as possible to ensure that it can still trap the cold air.

If the problem is not the insulation, but rather the gaps around the wood or vinyl from expanding and shrinking over the years, please see our article in this section on caulking.

Since the seal on a window is actually a variety of separate pieces, the source problem is difficult to find and fix. Fixing it correctly is especially difficult if you are looking to have the same high-quality finished look when the job is completed. For the perfectly finished job, it’s best to call CalFinder for a pre-screened professional. It is possible to do it yourself if you’re a diligent and detail-oriented person, but this route typically ends in DIY disaster. After all, the windows are the eyes and walls of your home. A botched job isn’t pretty.



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