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Sloped grade. Most basement water problems can be solved by properly sloping the ground around the house. The finish grade should slope away from the foundation at the rate of 1/2 to 1 inch per foot for 6 to 10 feet. A 2- to 4-inch cap of silty-clay material will keep runoff from percolating down through the backfill. A sloped grade will not work for long, however, if the perimeter fill is not mechanically compacted, which is rare in residential construction. Instead, compaction is left to chance and occurs slowly over a period of months or years, depending on climate and the type of backfill used. Gravels and sands percolate faster and may reconsolidate more quickly — typically, from three months to a year. Silts and clays, which have a much slower percolation rate, may not compact for several years. In either case, however, the result is a negative grade that directs runoff back toward the foundation. Depending on the type of backfill, sooner or later the runoff will overwhelm the footing drainage system, and basement water problems will appear. Silt or clay fill, which hold water longer than gravel or sand, can make the foundation more susceptible to cracking from frost action; hydrostatic pressure may also develop with these types of fill, forcing water through the slab-footing joint. Rarely will any of these problems appear immediately, but down the road, you’ll be faced with a messy and expensive repair job.

Gutters.

While gutters can dramatically reduce the total ground area onto which roof water drains, it is crucial to use a sloped leader to extend downspouts along the ground to carry water away from the foundation (Figure 2).

Downspout with Sloped Leader

Figure 2. Sloped downspout leaders should discharge at least 10 feet away from the foundation wall.

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Downspout with Catch Basin

Use solid drain pipe to carry runoff from a concrete catch basin to daylight or a drywell .

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Otherwise, a gutter-and-downspout system compounds the drainage problem by concentrating the entire roof runoff load into a few small areas, usually at the house corners. Leaders should discharge onto sloping ground at least 10 feet from the foundation. If downspouts dump directly into a catch basin on the surface or underground, the collected runoff should be carried through a solid drain pipe to a drywell or to daylight. Keep gutters clear of leaves, pine needles, and ice. Overflow from blocked gutters can follow the contour of the gutter and saturate the soffit and siding, often making its way into the wall and wetting the insulation, drywall, and floor. Similarly, gutters in cold climates can encourage ice damming, with the same damaging results.