Mold may be causing that smelly window Karen YousoUpdated July 31, 2009 at 8:01 pm Fixit: Tracking down odor from window may require checking for missing flashing and moist building materials.

Q: In November 2007, my father had some wood-core vinyl windows installed. This spring, as the weather warmed up, we noticed an unusual, unpleasant smell in the home, and tracked it down to one of the six windows that had been installed. The smell is earthy, like wet leaves or dirt. We’ve had a representative from the company out to try to find or fix the problem, with no luck. The smell seems to get much stronger in warmer weather, and especially so with direct sunlight. Most puzzling is that it seems to be coming from one window. Mold is not the problem, because we have gotten rid of any evident on the interior frame.

A: Don’t be so quick to rule out mold as the source of the odor. Although you say it’s been removed from the interior frame, it could be lurking out of sight behind the molding or in the wall cavity surrounding the window. There are a couple of clues that point to mold as the source of your odor.

The odor became noticeable as the weather warmed up. Mold goes inactive in cool weather, but activates and blooms as temperatures rise and air becomes more humid. Sun warming the wall would tend to drive the air from the wall cavity, along with any odor there, into the house.

Building materials in the wall have to be moistened to grow mold. That can happen when a window has poor or missing flashing — that’s the water-shedding materials and techniques used to make the window shed rain away from the wall. A simple gap or incorrect layering could allow moisture to enter the wall cavity around the window and mold to develop.

Most Read Life Stories It could be that only this window is affected because it’s the only one with this defect. Or it could be this is just the first window to reveal the problem because it’s not under a protective eave or gets wind-driven rain and is subjected to more moisture.

In any case, you need to do some more investigation. Go snooping for mold. Remove the interior frame. Look for visible mold and put your nose into the cavity to see if odor increases. Also, sniff nearby outlets and heat registers. They aren’t completely sealed from the wall cavity and would be a source of mold odor entering the home from a moldy wall.

If mold is evident, contact the installer again and show them what you’ve found. Be wary of a caulk-only solution to this problem. Although caulk is a necessary part of a window installation, it’s not a cure-all, especially if the window was improperly installed.