Stained and Rotten Window Sills

Have you ever opened a window and noticed that the wooden sill looks like someone spilled coffee on it? This is probably a water stain and is most likely due to inadequate installation of either the widow itself or the flashing or an improper seal between the two. Ever looked and seen that the sill is actually falling apart in the corners? This is rotten wood, and it likely started out as a stain. In this week's article we will dig into water and its effects on windows.

Stained or rotten window sills can be a source of anxiety for many prospective buyers. My job is to help if the stains are a sign of a major problem or something small that can be repaired simply.

3 Most common causes of stained and rotten sills.

1. Open Windows

Down east, it gets hot. We know this and night is often a welcome reprieve from the heat, but leaving a window open at night to capture that cool air can lead to problems. An open window during a rainstorm will obviously allow water into the house and will result in a uniform stain across the sill. So, just check the overnight forecast the next time you want that fresh midnight breeze. 2. Condensation

Condensation in large unchecked quantities is a big problem but small amounts is fairly normal, warm air on one side of the window cool on the other and when these two different temperatures meet on a neutral material - like glass - you get condensation. Just like ice water in a cup. Now, on a wood window, condensation will cause stains to appear at the corners of the window sashes and the window sills. Also, windows that are already more likely to be damp, such as in bathrooms or bedrooms just outside the bathrooms will have elevated levels of condensation staining. Airflow is key to maintaining proper moisture levels in bathrooms, hence, the fan.

3. Leaking windows

Leaking windows are a major concern. If water is actually getting into the house regularly due to a faulty window then this will typically show up as staining at the corners of the window sills. The photo slides below show a progression of what water damage looks like. On the left, minor water leakage in to the wall. Early enough to repair cheap and easy. In the middle we have advanced stages we're talking window, drywall and probably insulation but still early enough in the process that this could be taken care of. Now for the right, this is worst case scenario status. Here we have a window whose signs and symptoms were probably ignored and now there is damage to just about every aspect of the window, and yes, all that black stuff is mold.

The first two causes of stains are fairly straightforward and easy to prevent; remember to close the windows before it rains, and lower the humidity in your home. Leaking water from the exterior is the one that home buyers should be most concerned about. A slight defect in flashing or an improper bead of caulk and that window is going to leak. It could be just a little bit, but even a small amount of water is a big deal once it gets to the wood structure. Most unfortunately, it’s not easy for home inspectors (even those with 25 years of experience) to know if a window is going to leak.

Proper window installation will allow all of the water coming down the siding to be diverted around the sides of the window and onto the ground. In which case, the windows that will be exposed to the most water will be those that aren’t protected by roof overhangs.

Keep these issues in mind the next time you open a window in your home. Keep an eye out for staining on the sill, make a note of rotten sills and have them repaired sooner rather than later, and look at the weather before you leave your windows open overnight.

Thanks for stopping in, and as always, if you're in the market for a home inspector in North Carolina, go ahead and use my online scheduler to book your next home inspection! Until we meet in person,

Zac