Q: When we returned from vacation, after the house had been closed up for a week, there was a musty, mildewed smell. Each day, I noticed a musty smell in the bedrooms on the northwest side of the house. We replaced carpets in the last year and saw no indication of moisture.

Could there be mold inside the drywall? How can I figure out where the smell is coming from? By the way, my husband went under the house and says the pipes aren’t leaking.

A: There is a good chance fungus is growing in the walls. Fungus needs moisture and stagnant air to flourish. So find and fix the source of the moisture and it’s likely your problem will be solved. Be warned: You may be in for some drywall replacement.

On your husband’s journey under the house did he notice whether the dirt was damp? Damp earth in the crawlspace indicates either poor ventilation or a drainage problem. The cure for this is installing a sump pump.

If the crawlspace is dry, most likely water has been migrating into the walls from a roof leak or from voids around window and door frames. That there was no sign of moisture when you recently replaced the carpets leads us to believe the problem is recent.

Your first job is to determine if there is moisture in the walls. This can be done one of two ways. You can either hire a professional, who will probe the walls with a meter to determine if there is moisture, or you can cut out a few pieces of gypsum board at the base of the wall and take a look at the backside for mold.

If excessive moisture is evident or mold is apparent, you’re looking at replacing the gypsum board at minimum and possibly some of the wood framing as well. Because gravity draws moisture down, water from a leak will show at the bottom of the wall.

If mold or moisture is evident, the building envelope is compromised somewhere. Before replacing the drywall, you must find and stop the leak.

Look from the top down, starting with the roof. Roof leaks can be caused by anything from a cracked shingle at the top, to flashings around a chimney, to gutter and soffit areas.

If the roof is older we recommend you have it inspected by a licensed and bonded roofing contractor. It’s prudent to hire someone who has been in business for a long time. If an expensive repair is recommended, get other bids to assure yourself the price is fair.

If the recommendation is for a new roof, get at least three bids from bonded, licensed and insured roofing companies.

If the roof is OK, water may be migrating into voids around window and door openings. Inspect these areas to make sure they are well caulked.

Because the smell seems to be focused on north walls, it’s possible that condensation is the cause and air movement is the cure. Check out the vegetation. If it’s overgrown, trim it back to allow air to move.

A recap:

–Determine whether the walls have excessive moisture and mold.
–If moisture and/or mold are present, locate the source of the moisture and eliminate the source of the infiltration.
–When the moisture infiltration is stopped, replace the damaged gypsum board.

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