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Prevent Water Entry into Basements and Crawlspaces
Submitted by Lorene Bartos, UNL Extension Educator
Extensive rains across much of Nebraska this spring led to wet basements and crawlspaces. Rains, flooding, high groundwater tables, outdoor watering practices and water or sewage line backups can all cause water problems in homes.
There are many ways to prevent or reduce water entry. Start with an exterior inspection to identify potential entry sources, then inspect inside for water sources. Walk around the house just after a heavy rain to observe any problem drainage areas and low spots. Spray from a garden hose can help to identify water entry areas.
Before attempting any repairs or modifications, contact local code officials or the housing inspector’s office for specific requirements for your area.
The following checklist will help with the exterior:
* Ground surface slopes away from the foundation at a minimum slope of 5 percent (a 6-inch drop for every 10 feet of distance) to 10 percent (a 1-foot drop for every 10 feet) for the first 10 feet and then continue the slope away at a minimum of 2 percent. Paved surfaces near the foundation slope away at a minimum slope of 1 percent to 2 percent (an eighth to one-fourth of an inch drop for every 1 foot of distance).
* Water runoff from adjacent buildings, lots and concrete surfaces should flow away from the house foundation.
* Water flowing toward the house should be intercepted and moved toward a dry well or into street drains, or in some situations, surface outlets. Options may include use of retaining walls, terraces or drainage areas such as swales, or shallow open channels. French, channel, trench or soil strip drains, grate drains or inlet basins can be used for subsurface drainage. Check with local code officials for appropriate options.
* A landscape's natural features can absorb water. Porous materials can be used for sidewalks and driveways. Rain gardens, cisterns or other methods also can be used to absorb or capture some of the water.
* Foundation concrete, brick or other materials show no signs of deterioration. There are no foundation cracks, bulges or signs of settling.
* Gutters are clear of debris, in good condition and direct water to down spouts. Gutters and down spouts are correctly sized to prevent over flow in heavy rains.
* Down spout extenders are in place and direct water 6 to 10 feet away from the foundation.
* Concrete slabs, patios, sidewalks, steps and driveways attached to the house slope away from the house. Joint areas between the foundation and other materials are filled with appropriate sealants or gaskets to prevent water entry. Expansion joints are in good condition.
* Areas where two different materials meet are filled with appropriate sealants or caulk.
* Weatherstripping protects against moisture entry around doors, windows and window air conditioning units.
* Basement windows prevent water entry. Window wells have adequate drainage and drains are not plugged. Window wells extend at least two inches above surrounding soil. Any window well covers in place are correctly sized and direct water away from the window well area.
* Exterior basement doors are sturdy, correctly installed, flashed and weatherstripped to direct water away.
* Utility entrances in exterior walls are correctly flashed and sealed to prevent water entry.
* Drip caps or drip edge flashing direct water away from bottom door edges.
* Flashing and correct sealants are used around roof penetrations, chimneys, and at soffit edges to direct water down and to the exterior of the home.
* Roof valleys are protected with flashing or membranes and direct water down and to gutter areas.
* Flashing is correctly installed, secured and wide enough to protect areas where roof shingles meet a wall.
* Flashing and gutter aprons protect the eave edges and fascia or face board. Drip cap edges along the roof edges moves the water away from the face board.
* Overhangs are at least 18 inches wide to help direct water away from the house.
* Decorative borders and plants do not trap water next to foundation.
* Water from sprinklers does not hit the house.
The following checklist will help with crawlspaces:
* Flood vents, if present, are large enough to handle the potential water flow.
* The crawlspace surface drains water from center outward. Crawlspace grade should be higher than the outside surface grade.
The following checklist will help with the interior:
* Basement water and sewage lines have back-flow devices.
* Basement and crawlspace floors and walls are free of cracks or deterioration.
* Areas around windows and doors are weatherstripped and sealed with appropriate sealants.
* Basement and foundation walls are upright, straight and in good condition.
* Water stains are not evident on walls or floors.
* Water hoses, pipes and connections are secure and in good condition.
The following checklist will help with hidden construction areas:
* A moisture barrier was installed underneath the slab when basement, slab or crawlspace floors were poured.
* If foundation footing drains are present, they are not blocked and were installed to direct water away from the footings.
* Below grade concrete or block walls are damp-proofed or waterproofed and coated with appropriate exterior sealants to reduce water entering through the wall.
* Fill-soil around the foundation was adequately packed. Correct materials and processes were used to provide drainage to footing drains. An impervious layer of clay or bentonite under the top soil adjacent to the foundations acts as a "ground roof" to direct water away from the foundation.
If problems persist, exterior foundation drainage system, interior perimeter baseboard gutter drainage systems, sump pumps or interior foundation drains are sometimes installed. Sump pumps should discharge water well away from the house.
Consulting with local code officials or housing authorities, and obtaining information from qualified professionals, experienced building contractors or a professional engineer are important steps before making decisions about the potential options.
Contact InformationUniversity of Nebraska-Lincoln in Lancaster County
Web site: lancaster.unl.edu
444 Cherrycreek Road, Suite A, Lincoln, NE 68528 | 402-441-7180