extend downspouts away from house
Illustration: Tom Moore
EXTEND DOWNSPOUTS at least 4 ft. away from the house and install a splash block to help disperse the water.

Rainwater or melted snow that isn't routed away from the house is the most common cause of basement and crawl space moisture. Runoff percolates through porous topsoil and then stops at the compact soil near the base of the foundation. Hydrostatic pressure forces the water through gaps or cracks in walls and footings. Water also moves through porous walls by capillary action.

Diagnosis. A damp crawl space or wet basement walls and floors just after a storm or as snow melts are telltale signs the problem is runoff.

Look for ways runoff can enter your basement or crawl space. Check that the ground outside slopes away from your house at least 1 inch vertically for every 1 foot of horizontal travel. Then make sure downspout runoff isn't pooling or percolating into soil near the foundation during a storm, and that downspout seams aren't leaking; installing downspouts seams-out makes this check easy.

Next, check that driveway curbs are channeling runoff to the street. Look for unsealed cracks on the driveway surface, which can allow water to collect below grade. Some houses on hilly sites have a swale a shallow trench with gently sloping sides and a gravel bed covered by topsoil and grass. The swale catches runoff, channeling it past the house or off to other drain systems. Unfortunately, a swale can eventually clog with silt. So can the original underground footing drains buried at the base of your foundation.

Simple cures. If you're dealing with a full basement, start by patching cracks in the foundation and sealing basement walls. Use a polyurethane masonry caulk like Sikaflex ($7 per tube) or UGL's Masonry Crack Filler (about $5 per tube). For 1/4-inch or larger cracks, use hydraulic cement, which expands as it dries. Leading products on the market include Thoro Waterplug (about $16 for 10 lbs.), Custom Building Product's Custom Plug (about $14 for 12 lbs.) and UGL's Fast Plug (about $20 for 10 lbs.).

For both basements and crawl spaces, you need to address outside entry points next by patching cracks in the driveway using cold-mix asphalt patching compound. For a concrete sidewalk or driveway, use ordinary cement.

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