March 3rd, 2015

Damp Basements and Crawlspaces

Home Owners Network

Questions about damp basements and crawlspaces are a frequent subject at our “Ask The Experts” service. Let’s discuss some common issues related to this defect so we can understand whether and how to deal with them. We will not discuss problems caused by high water tables and underground springs. A qualified contractor should deal with these problems.

 You should remember the letter G when thinking about dampness around and under your home.  G stands for grading and gutters. Grading means establishing and maintaining slope away from your home’s foundation. Gutters means a system at the eaves that captures rain water from the roof and empties it into downspouts that direct the water away from your home’s foundation. Get the “Gs” right and you’ll solve many of the dampness problems in basements and crawlspaces.

 Current accepted construction standards recommend sloping earth away from your home at a rate of at least six inches in the first ten feet. Hard surfaces, such as driveways, patios, stoops, and porches, should slope at least ¼ inch per foot away from your home. Surface water that collects around your home is much more likely to find its way into your basement or crawlspace.

 All homes should have a system of properly installed and well maintained gutters and downspouts. Gutters are called eaves troughs and downspouts are called leaders in some regions. Gutters should slope toward the downspouts. As little as 1/32 inch per foot slope will do. Downspouts should deposit water at least three feet away from the foundation. Terminate downspouts in splash blocks, extension pipes, or underground drains. 


 You should establish a regular schedule for removing debris from your gutters and checking them for improper slope and leaks. Gutters blocked by debris and gutters that leak won’t direct water away from your home. Your schedule depends on how many trees are near your home. Once per year may be adequate for homes with few trees nearby. Every six to eight weeks may be appropriate for heavily wooded lots, especially in the fall. Safety Warning: cleaning gutters involves ladders and falling off ladders is a common and serious household accident. Hire someone to clean and inspect your gutters if you’re not comfortable on a ladder. This cost is part of your home maintenance budget.

 Sometimes it’s not practical to establish good slope away from your home; then what do you do? Underground drains, sometimes called French Drains, may be an answer. You may connect buried plastic pipes to downspouts, or to water collection basins (called catch basins), or to dry wells and use this system to capture rain water and direct it away from your home.

 Water flows downhill, so underground drains need some place downhill from the foundation to discharge the water. If there is no convenient place, it may be necessary to pump the water away.  This is when you consider installing a sump pump. Sump pumps are usually installed within the basement or crawlspace, but they may be installed outside too (in warm climates). If installed in a basement, the sump pit should be sealed to reduce moisture in the basement. Sealing the sump pit is essential in Radon-prone areas for both basements and crawlspaces. The pump should be protected by a GFCI electrical circuit. Power failure and overflow alarms are a good idea, especially in a finished basement.

 You should avoid directing water toward your home from systems such as your irrigation system. Don’t plant high water use plants (including grass) near your foundation. Don’t plant large trees near your foundation. Remember that tree roots usually extend at least as far as the tree branches. Extend your air conditioner condensate drain pipe about one foot from the foundation. Check your irrigation system regularly and make sure it isn’t spraying the house.

 If your basement or crawlspace is still damp after trying everything else, then more aggressive (meaning more expensive) measures may be appropriate. These measures may be necessary if you intend to finish your basement. First, though, let’s address one method that may not work well. Trying to stop moisture infiltration using coatings applied to the interior walls might help with minor moisture infiltration, but these coatings often do not help with more serious moisture problems.  Serious moisture problems are usually best resolved from the outside.

 The problem with attacking moisture from the outside after the home is built is the high cost of removing the plants and dirt from around the foundation and replacing them when the job is done. Cost is why many people try, often unsuccessfully, to attack the problem from the inside.

 The current minimum accepted standard for new homes with basements is to apply a dampproofing layer on the outside of the foundation and to install foundation drains around the perimeter at the footings. Modern damp proofing usually involves spraying a tar-like substance on the outside of the basement walls. Damp proofing and foundation drains are not required for crawlspaces, although they are a good idea. Homes older than about fifty years may or may not have been damp proofed, and even if they were, there’s a good chance that the dampproofing is no longer effective.

 If finishing the basement is anticipated, waterproofing the outside of the foundation walls is recommended. Waterproofing is more effective at stopping water infiltration and should last longer than dampproofing. Commercial waterproofing systems are one option that sometimes provides insulation in addition to waterproofing. The other options include waterproofing coatings and materials like six-mil polyethylene. Foundation drains are recommended for waterproofing too.

 Correcting minor grading problems and installing downspout extensions and splash blocks are often do-it-yourself projects. You should seek advice and help from a qualified contractor for more difficult projects.

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