Moisture Problems Crawl Spaces

The Old House Web

Here aresome tips on diagnosing and correcting moisture problems. Parts of this story: ~~Introduction~~ Attic andmechanical ventilation ~~ Houseson crawl spaces and other moisture sources ~~ Caulkingand weather-stripping ~~ Basementwall condensation problems

Houses on crawl spaces

In homes built on crawl spaces, evaporation ofmoisture from the earth is a major source of householdhumidity. The high levels of humidity in crawl spaces canbe a problem in both summer and winter. Foul odors in thehome or crawl space, mold and mildew growth in theinterior of the home (especially in closets) and growthof fungi in the crawl space itself are signs of theproblem. Covering the crawl space ground with a vaporretarder (polyethylene or heavy plastic sheets availableat lumberyards) is crucial in preventing moistureproblems in crawl space homes.

In addition to a vapor retarder covering the ground, crawlspaces should be provided with adequate natural
ventilation to facilitate air movement throughout thespace. If a vapor retarder is present in the crawl space,1 square foot of free vent area is required for every1,500 square feet of crawl space ground area. Without avapor retarder present, 1 square foot of free vent area isrequired for every 150 square feet of crawl space groundarea.

Most crawl space vents include louvers and/orscreens to prevent the entry of insects and small animals.These coverings slow air circulation and cut down on thevent's effectiveness. Thus, you will need to double the
amount of ventilation needed in most cases to compensatefor this reduction. Locate vents near corners and acrossfrom one another to facilitate air movement through thecrawl space.

Other moisture sources


Many homeowners use humidifiers to add moisture totheir homes in winter. In the past, when homes were leakyand so less energy efficient, much of the moisturegenerated inside the home went out with the warm airescaping around and through windows and doors.

Overly dry air-was common, and people experiencedstatic electricity buildup on carpets and clothes,breathing difficulties due to dry nasal passages andsomewhat destructive over drying of furniture. To combatthis dryness, they commonly used humidifiers. Some wereincorporated directly into forced air heating systems, andmoisture was circulated in the home along with heated air.A second type of humidifier, the free-standing model, isportable and can be moved freely around the home toprovide moisture where it is most needed. Whether you haveextensively weatherized your home or not, experiencingcondensation problems means you should not use ahumidifier.

Construction moisture

Homeowners who move into a: newly constructed home orcomplete remodeling projects often experience highmoisture levels in the interior as the building materialsand systems dry. If it is necessary to close the housebecause of cold weather, the problem may seem excessivelyserious. Over time, the building materials will dry and aform of equilibrium will be established. In the meantime,airing the house when you can and using exhaust fans willhelp to move the moist air to the outside.

Malfunctioning combustionappliances

Oil- or gas-fired heating, appliances that are notfunctioning properly or unvented heating units can cause abuildup of moisture in a dwelling. If you suspect anycombustion appliance in your home is not functioningcorrectly, have a repair person inspect it. Heatingsystems, in particular, should be regularly inspected andadjusted by a heating contractor. Oil-fired furnaces needannual inspections. Gas-fired systems, depending on theirage, can be inspected less frequently, though three yearsis the maximum time a gas-fired unit should go withoutbeing serviced. If you use unvented space heaters in thehome, follow the manufacturer's use and maintenanceinstructions carefully.

Cool surface condensation problems

In less energy-efficient homes, cool surfaces arereadily available for water vapor to condense and collecton. Warming these surfaces by adding insulation orcutting down on the amount of cold air that can get tothem by caulking and weather-stripping will lessencondensation problems.

Toilet Tank and Water Pipe Surfaces

Toilet tank surfaces are another common place forcondensation to occur, particularly during warm, humidmonths. Warm toilet tank surfaces by either installingrigid waterproof insulation on the inside of the tank oradding a mixing valve to the cold water supply line. Thisintroduces hot water into the tank water supply and can
help warm the tank to a level that prevents condensation.Install tubular or wrap insulation around water pipes to
prevent condensation there.

The informationin this article comes from Michigan State UniversityExtension bulletin E-2109, Moisture Problems in the Home.

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