Q: We have a split-level home built in 1953 with a 1967 addition. The lower level has a musty odor, and when we removed the baseboards, the base of the wall was furred with white mildew/mold. We then removed some of the "Brady Bunch"-style paneling and the drywall also has patches of black and white mold extending irregularly up several feet.

Outside, the stucco runs all the way into the soil. The addition that includes the room with the problem projects into the backyard on a concrete slab and thus has exterior walls on the north, east and south sides. The lot is on a slope but has been graded flat and divided into two terraces by a low, brick retaining wall.

The south wall (downhill side of the house) has mold as high as 7 feet above the slab, although the worst is the bottom 2 feet. The only downspout in this section is on the east wall, where it empties onto a concrete pad and then onto the brick walkway and into the yard. The east wall doesn’t seem to have any mold.

We are remodeling and want to identify and deal with the source of the moisture before insulation and drywall. One person has suggested that the cause might be that our stucco runs all the way to the ground and could be wicking up moisture. Another believed that the exterior walls might have been half-stuccoed before and that the conversion to full-length stucco left a seam open to water penetration midway up the wall. Do either of you have any recommendations for companies or people that deal with the above situation?

A: We have to stay neutral and must refrain from recommending a specific company or contractor for any job. We do give direction on the type of contractor to use for a specific job.

The most important thing you can do is to channel the water coming off the roof away from the house.

You should look first to a roofing contractor for proper gutters and downspouts, and then to a landscape contractor to identify and solve the drainage problem we’re convinced is the source of the mold. Finally, we recommend you have an insulation contractor spray expanding foam insulation to act as both an insulator and a vapor barrier.

Mold requires water to grow, but we don’t think the cause is moisture wicking up the stucco or water penetrating a seam in the stucco.

We can’t believe water is wicking 7 feet up the wall. To rule out the seam theory, make a thorough visual inspection of the exterior wall. Believe us, if a seam is the problem, you’ll notice it. But if there is a problem with the seam, the simple fix is to caulk the seam with elastomeric caulk and repaint. Elastomeric caulk stretches, and a crack repaired with this product is less likely to reopen.

A couple of things you mention provide clues to the possible source of moisture penetration. The fact that there is no mold on the east wall — the only one with a downspout to channel water away from the foundation — is telling. Consider installing gutters with downspouts on the other sides of the house, especially on the south side where the mold is most prevalent.

Make sure the downspouts direct the water far enough away from the foundation so as not to saturate the soil around the foundation footing.

If local code allows, a good solution is dumping the roof water in the downspout into an underground drainpipe that enters into a dry sump located downhill from the south wall. This should be a relatively inexpensive job — especially if you dig the ditch and install the drainpipe and dry sump yourself.

Put your remodel on hold for a little while to make certain the moisture problem is solved. In the meantime, kill the mold with a solution of 1 part chlorine bleach to 2 parts water delivered to the moldy areas with a spray bottle. Make sure the room is well ventilated when you do this.

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