Standing water inside and/or seepage into residential crawl spaces and basements can cause frustrating problems for the homeowner. These problems can be both immediate and long term.
Wet basements and crawl spaces are sources of high humidity, which
can produce surface condensation, mildew and fungi, musty odors, and an
unhealthful environment. Such moisture can cause deterioration of floor
joists, beams, subflooring, insulation, and electrical-mechanical
systems. Prolonged water around the footer and foundation wall can
soften the soil and weaken its bearing capacity, increasing the
possibility of wall settlement and cracking. Serious seepage under the
foundation footer may erode soil away and cause the wall to drop or
Excessive moisture can eventually penetrate the subflooring
and buckle the flooring or cause warping, making doors and cabinets
difficult to close or open. Since crawl space or basement dampness
always moves toward the drier upstairs areas, higher humidity will
result in costlier heating and air conditioning bills. In the case of
crawl spaces, if the underflooring insulation collects moisture, or sags
from excessive wetness, the heating and air conditioning costs are
driven even higher. Finally, wet basements and crawl spaces reduce the
value of the house--at least by the amount that would be required to
repair the damage and to eliminate the cause of the problem. Some
homeowners are reluctant to discuss or admit their water problem, for
fear that the publicity of an actual or even a perceived problem would
reduce the value of their investment. Homeowners, in such situations,
should immediately seek professional assistance in assessing the source
and extent of the problem and in finding a remedy.
CAUSE OF WET BASEMENTS AND CRAWL SPACES
wet basements or crawl spaces are caused by surface water which is not
adequately drained away from the foundation wall. Sources of this water
include the following:
Roof water if no guttering is present
Roof water if the guttering leaks or overflows because of clogging from leaves and bird nests
water if the downspouts (leaders) are clogged or do not have sufficient
means at their outlets to drain water away from the foundation wall.
Frequently, a downspout ends at the corner of the house without a splash
pad (splash block) or elbow (shoe), leaving roof water to concentrate
at that point and seep into the soil next to the foundation wall. A
typical 2000 square foot roof can produce almost 1250 gallons of water
during just 1 inch of rainfall. If the rainfall is steady and prolonged,
the opportunity for this roof water to soak into the ground next to the
foundation wall is high.
Excessive watering of flower
beds and shrubbery around the foundation wall. Once the upper soil layer
or mulch bed air spaces are filled with water, the excess water either
runs off or seeps into the ground next to the wall. Prolonged and
excessive watering can contribute a large amount of water to crawl
spaces or basements.
Rainwater runoff from the adjacent
lawn, walks, or driveway areas if the landscaping forces water to drain
toward the house instead of away. If surface runoff is directed toward
the foundation wall, this water will pond and eventually soak into the
soil, thus becoming a potential source of basement or crawl space water.
Downspout splash pads are not very effective if they drain onto a
backward-draining slope toward the foundation wall.
Water or dampness problems in basements or crawl spaces are sometimes caused by other factors:
or groundwater may be intercepted or dammed up by a basement or
foundation wall. Houses which are built downslope on or at the base of
hillsides are particularly vulnerable since there is greater opportunity
for surface water to soak into the soil to become groundwater and
because groundwater flows downhill by gravity. Foundation walls act like
dams and can intercept and trap this subsurface water, causing pressure
build-up on the outside and forcing water through joints and cracks in
basement walls or seepage under the footer.
springs may have been filled in or covered up by the developer. Unless
the springs were properly drained away from the lot or subdivision, such
water will eventually seep into the surrounding fill, become a pool of
groundwater, and eventually force itself laterally and upwardly into
basements and crawl spaces.
Nearby creek(s) may
overflow during storm runoff and either directly flood basement or crawl
space areas, or contribute to the groundwater, which may become
sufficiently high to cause seepage into the basement or crawl space
area. Homeowners may not experience the effects of groundwater seepage
or overflowing creeks for months or years after purchasing a house
because of drought or infrequent out-of-bank flooding. However, when
such conditions do occur, they may come suddenly without warning and
cause serious problems after the warranty period has expired.
installed, clogged, collapsed, or leaky drains may not allow downspout
water or foundation wall water to escape. Perimeter, footer, or
foundation drains are installed around the exterior of a house below the
basement floor to intercept and dispose of subsurface water to
eliminate groundwater build-up and seepage under the house. If these
drains are improperly installed or become clogged with silt or roots,
they will not operate as intended. Sometimes an otherwise good perimeter
drain gets covered up at its end(s) during the final backfilling or
landscaping stages of construction and the intercepted water has no
place to go but to build up behind the foundation wall and eventually to
seep into the basement or crawl space.
drains leading away from downspouts may not have sufficient slope to
carry water away; may empty into the adjacent lawn and get covered with
topsoil; may become crushed during landscaping or become pinched at
their outlets; or may lead to an area which ponds and backs up water.
The end result in all these cases is leakage or overflowing at the
bottom of the downspout and water penetrating the foundation area.
PREVENTING AND REMEDYING WET BASEMENTS AND CRAWL SPACES
Generally, surface water drainage should be directed from all sides of the house and off the lot in a manner that will
Minimize possibility of dampness in basements and crawl spaces
Prevent standing or ponding water on the site
Prevent soil erosion
Adversely affect the supporting foundation soil behavior.
driveways, retaining walls and other landscape improvements should be
constructed so as not to interfere with drainage. Walks should not be
used as drainage channels.
Site grading plans should specify
minimum slopes from the house (usually 2 to 5%), depending on location,
type of soils, frost depth, and soil moisture, to ensure water drainage
for some specified distance usually 6 to 25 feet away from supporting
foundations. In cases where minimum slopes or distances cannot be
attained, paved gutters or other drainage structures acceptable to the
Building Inspector may need to be installed.
Maximum slopes are usually specified to prevent erosion or unstable banks around the house and yard.
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