Windows are, quite often, just accepted without question. They came with the home. It’s not until the towel brigade is mopping up water from a closed window sill that homeowners begin taking a hard look at their windows in general.
Windows are, quite often, just accepted without question. They came with the home. It’s not until the towel brigade is mopping up water from a closed window sill that homeowners begin taking a hard look at their windows in general. REALTORS® don’t start taking a hard look at the windows until the window either falls apart during an inspection or fails a moisture test.
As an inspector focusing on the exterior of homes and buildings, I’ve seen my fair share of windows. Based on our own survey of 2,000 homes of random ages, windows and/or the window openings themselves account for 24.8 percent of moisture problems in walls. This means that the average home with, say, 10 windows has 2-3 potential leakers causing damage to the structure of the home.
What the statistics don’t tell you is that every window will fail under the right circumstances. Building codes for different climates require windows to meet certain minimum conditions for wind load, thermal transfer, air and water leakage, etc. Given that every manufactured window has a failure threshold, every window will leak at some point. There are two basic kinds of leaks with windows: leaks to the interior of the home that require clean up with a towel (towel leaks) and leaks into the wall cavity that you don’t see (rot leaks). Towel leaks are usually caused by the seal failures between the window sash or glass and the framework of the window. The sash seal usually ends up permanently compressed, worn-out or missing, allowing for both air and water leaks. The potential wetting of the window frame and/or sash on a year-round basis can lead to the window sash falling apart during the home inspection. Towel leaks should have the cause determined and dealt with quickly to avoid growing into a rot leak. Seal replacement, sash adjustment, caulking, and TLC may be all that is needed; however, sometimes window replacement is a more viable option, since time, gravity and water always win in the long run.
Rot leaks occur through or around the frame of the window. The frame is the fixed part of the window that is attached to the structure of the home. Rot leaks through the frame typically occur at the lower outside corner joints of the exterior window sill. This is where the vertical frame member meets the horizontal frame member. This joint often opens and fails due to climate-induced expansion and contraction of the window, movement or shrinkage of the wood structure after window installation, improper installation techniques, UV rays, poor window design, etc. Water that the towel brigade missed usually enters the wall cavity through the corner joints. Most of the time, caulking these joints with a clear silicone using proper technique will prevent leakage through the joint. Not all corner joints are suspect to failure because of the manufacturer’s design, and caulking the joints in the wrong places on some windows is not recommended. Always follow window maintenance procedures from the manufacturer or builder.
Rot leaks also happen when there are open gaps between the frame and the cladding/siding of the home. These gaps allow water in at the lower outside corners of the frame and or below the window sill. Many homes are not caulked, and if they are caulked, the caulking is either weathered, failing or unprofessionally applied. Open
gaps around windows are potential funnels into the wall cavity. Once all of this water is in the wall cavity, it’s only a matter of time before damage will begin without any outward signs.
The good news is that rot leaks are diminishing in quantity. Rotting windows, class action lawsuits and abundant construction defect claims have caused the construction industry to take note and to make adjustments to both building code and best practices. No longer are the windows and window openings considered two independent parts of the home. They are both integrated to deal with expected window failures and preventing water entry into the wall cavity of the home. Theoretically, window-related water entry into the wall cavities should be a non-issue in 2003 and newer homes; however, realistically, windows still leak and human-error is always a factor.
As a REALTOR® looking at a home to list or sell, understand what you might not be able to see in the wall cavity. Look for the visible signs of rot in the walls – staining on the window sill or sash, windows not caulked or flashed on the exterior, rotted siding around the window, stains on the window dressings, stains on the window header, and, my favorite, mushrooms growing from the window. After all, windows are not just for the view; they are to provide basic comfort, safety and structural soundness for the occupants.