Exterior Surface Grading
The grade or slope of the soil should be designed to direct surface water away
from or around the home. Water accumulation next to the home can lead
to water penetration problems such as structural damage to wood framing,
interior damage to finished surfaces and damage to the homeowners'
belongings. Additional problems such as hydrostatic
pressure against foundation walls or surface water mixing with expansive
soils next to or under a foundation can lead to cracking of the slab
and foundation walls. Proper grading (in conjunction with a gutter
and downspout system) is one of the easiest ways to manage surface
water, reduce the possibility of water
penetration and structural damage
from hydrostatic pressure, and control the water content in expansive
soils.
Grading of the Soil Around the Perimeter of
the Home
The soil around the perimeter of the home should slope away (at a minimum of
six inches for the first 10 feet) from the house to prevent rain water from
accumulating next to the foundation. Soil in this case does not
refer to the topsoil but the layer of soil that is impervious to water such
as clay, which directs the water away from the house. Many times the topsoil is porous (as would be used for planting) and absorbs
the surface water. The sub-layer of clay or similar non-porous soil
prevents the water from continuing in
a downward movement and directs the water
laterally. If non-porous soil next to the foundation slopes
toward the house, water will begin to accumulate.
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Grading of the Lot
The overall lot grading is also an important concern since surface water
may enter from adjacent properties. Generally, if the house is located
on a slope or on a lot that receives water run-off, swales are often used to
direct the water around the house. Swales are shallow ditches or
depressions in the landscape that capture the water run-off. Then,
like a small creek, the water is directed around and away from the house.
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