WET BASEMENT AND CRAWL SPACE
PROBLEMS, CAUSES, AND REMEDIES --TIPS FOR
HOMEOWNERS, AND HOME BUYERS

BY
DR. BRUCE A. TSCHANTZ, P.E.
btschant@utk.edu
PROFESSOR EMERITUS
UNIVERSITY OF TENNESSEE
KNOXVILLE, TENN

 

The primary purpose of this guideline is to provide basic information to the homeowner, home buyer, landscaper and home builder about the causes of wet basements and crawl spaces for making practical decisions in purchasing pre-owned or new homes, preventing or correcting problems, and for repairing affected homes. The contents of these guidelines are also intended to provide a common basis of communication among the homeowner or buyer, local codes official, realtor, builder/contractor, inspector/regulator, insurer, and mortgager.

Contents:

WET BASEMENTS OR CRAWL SPACES--SOURCES OF IMMEDIATE AND LONG-TERM PROBLEMS.

CAUSE OF WET BASEMENTS AND CRAWL SPACES

PREVENTING AND REMEDYING WET BASEMENTS AND CRAWL SPACES

TIPS FOR HOME BUYERS, HOMEOWNERS, AND HOME BUILDERS

 

WET BASEMENTS OR CRAWL SPACES--SOURCES OF IMMEDIATE AND LONG-TERM PROBLEMS.

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. For example, standing water and mud inside crawl spaces make it very difficult and messy to gain safe access under the house for inspecting, maintaining, and servicing electrical circuits, drains and water lines, heating and air conditioning, and other utilities. Wet basements and crawl spaces are sources of high humidity, which can produce surface condensation, mildew and mold fungi, musty odors, and an unhealthful environment which can cause or aggravate respiratory problems. 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 crack. 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 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 adverse publicity of an actual or even perceived problem, would reduce the value of their investment or perhaps difficult to sell. 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

Most 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:

Water or dampness problems in basements or crawl spaces are sometimes caused by other factors:


Figure 1. Typical paths of water and moisture into a crawl space area.

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PREVENTING AND REMEDYING WET BASEMENTS AND CRAWL SPACES

The International Residential Code (IRC), published by the International Codes Council (ICC), for 1- and 2-Family Dwellings (R401.3), requires that "Lots shall be graded to drain surface water away from foundation walls. The grade shall fall a minimum of 6 inches within the first 10 feet." Many local governments have adopted this or similar building codes.

The Federal Housing Administration (FHA) of the Housing and Urban Development (HUD) Agency generally relies on the code adopted by local ordinance where FHA mortgages are insured. In case there is no local code, the appropriate FHA/HUD Field Office will specify a building code that is comparable to one of the nationally recognized building codes.

Generally, surface water drainage should be directed from all sides of the house and off the lot in a manner that will

Walks, 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 4 or 5%), depending on location, type of soils, frost depth, and soil moisture, to ensure water drainage for some specified distance (usually 8 to 25 feet) away from supporting foundations. In cases where minimum slopes or distances cannot be attained, paved gutters, swales or other drainage structures acceptable to the Building Inspector will need to be constructed to ensure adequate drainage away from each structure. Impervious surfaces near the house, such as sidewalks, patios, parking areas, and drives, need to be sloped away. (see IRC R401.3).

Maximum slopes are usually specified to prevent erosion or unstable banks around the house and yard.

Roof water should be directed to a downspout and away from the foundation wall toward a suitable ditch, swale, or drainage pipe to prevent ponding or backflow as shown in Figure 2. All drainage structures should be properly connected to adequate outlets that are protected, where necessary, by recorded permanent easement.

 


Figure 2. Correct installation of downspout shoe and splash
block at foundation wall. Note that ground surface should slope away from house to be effective.

House plans and landscaping should be developed to prevent "dead" drainage areas around the foundation wall--areas where rainfall has no place to flow away except by ponding and soaking into the soil near the foundation wall. Flowerbeds and mulched landscape areas bounded by the front entrance/sidewalk/garage/driveway are especially vulnerable to trapped pockets of surface water which easily soaks into the soil next to the foundation wall.

Adjacent creeks, drainage swales, rivers, and lakes should be checked for historic or calculated flood hazard levels. Usually, first-floor or habitable space floor elevations are required to be above the level of a 100-year return frequency flood; however, more frequent flooding may be allowed in crawl spaces and certain basements. Homeowners should be aware of, and home builders should comply with, local development code requirements and FEMA's National Flood Insurance Program (NFI) local flood risk maps.

In older houses where any of the above defensive or primary moisture and water control methods are missing, measures should be taken to install appropriate exterior roof, surface and groundwater drainage, vapor barriers, or ventilation openings. Installing any of these elements after a house has been built will be more costly than while the house is constructed.

In some cases it may be necessary to use secondary measures to alleviate a wet basement or crawl space problem--either along with the above measures, depending on the situation. Additional measures include the following:


Figure 3. Correction of reversed slope drainage problem using swale or ditch

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TIPS FOR HOME BUYERS, HOMEOWNERS, AND HOME BUILDERS

"A teaspoon of prevention is worth a gallon of cure" certainly applies to new home builders--at least in avoiding water problems in basements or crawl spaces. Buyers of new or older homes should be cautious about drainage. The best time to sign a contract is on a rainy day!

New home buying/building tips

The following tips are suggested to avoid water problems when building or buying a newly-built home:

Older home buying tips

The following recommendations are made to the prospective older home purchaser:

Tips for homeowners who currently have water problems

Summary and Resources

Make use of local organizations, governmental offices and experts if you have concerns about drainage around your house or about wet basement or crawl space. Check with people from these organizations for professional services or recommendations:

Some problems may be solved simply by repairing an obvious gutter or downspout leak, while other problems may have causes which are difficult to identify and very expensive to fix. Severe crawl space water problems may cost several thousand dollars to remedy. Always use a competent professional to help you FIND AND ELIMINATE THE SOURCE of your problem BEFORE REMEDIATING inside damage. Don’t settle on quick, bandaid approaches which merely deal with the inside symptoms of basement or crawl space water problems.

Above all, remember that in many home purchases, it’s BUYER BEWARE!

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Examples of Wet Crawl Space Problems

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