1.5   Reducing Moisture Problems

Moisture causes billions of dollars worth of property damage, sickness, and high energy bills each year in American homes. Water damages building materials by dissolving glues and mor­tar, corroding metal, and nurturing pests like mold, dust mites, and insects. These pests, in turn, cause respiratory illness.

Water reduces the thermal resistance of insulation and other building materials. High humidity also increases air-condition­ing costs because the air conditioner removes moisture from the air to provide comfort.

The most common sources of moisture are leaky roofs and damp foundations. Other critical moisture sources include dry­ers venting indoors, showers, cooking appliances, and unvented gas appliances like ranges or decorative fireplaces. Clients con­trol many of these moisture sources, so educate them about how to reduce the moisture sources discussed here.

Climate is also a major contributor to moisture problems. The more rain, extreme temperatures, and humid weather a region experiences, the more of its homes are vulnerable to moisture problems.

Moisture and humidity are problems in building because of con­densation and wetting, elevated moisture content, and discom­fort in the summer.

Reducing moisture sources is the first priority for solving mois­ture problems. Next most important are air and vapor barriers to prevent water vapor from migrating through building cavi­ties. Relatively tight homes need mechanical ventilation to remove accumulating water vapor.

1.5.1   Symptoms of Moisture Problems

Condensation on windows, walls, and other cool surfaces sig­nals high relative humidity and the need to reduce moisture sources. During very cold weather or summer air conditioning, condensation may occur on cold surfaces. This occasional con­densation isn’t a major problem. However, if condensation is a persistent problem, reduce moisture sources. Adding insulation helps eliminate cold walls, ceilings, or air-conditioning ducts where water vapor condenses.

Moisture problems arise when parts of the building become wet often and stay wet for periods of time. Moisture in organic or porous building materials reaches a threshold that allows pests like mold, dust mites, and insects to thrive. These pests can cause or aggravate asthma, bronchitis, and other respiratory ail­ments because they produce potent biological allergens.

Rot and wood decay indicate advanced moisture damage. Unlike surface mold and mildew, wood decay fungi penetrate, soften, and weaken wood.

Peeling, blistering, or cracking paint may indicate that moisture is moving through a wall, damaging the paint and possibly also the building materials underneath.

Corrosion, oxidation, and rust on metal are unmistakable signs of moisture problems. Deformed wooden surfaces may appear as the damp wood swells, and later warps and cracks as it dries.

Efflorescence is a white, powdery deposit left by water that moves through masonry and leaves minerals from mortar or the soil behind as it evaporates from the masonry surface. Concrete and masonry efflorescence indicates water movement through the home’s foundation.

Lesson: Moisture and Relative Humidity

View this lesson to learn more about the relationship between moisture and relative humidity, and the problems they can pose in buildings.

1.5.2   Solutions for Moisture Problems

Preventing moisture problems is the best way to guarantee a building’s durability and its occupant’s respiratory health. How­ever, the solutions get progressively more expensive if simple solutions don’t solve the problems.

Inexpensive Moisture Solutions

If moisture source reduction isn’t adequate to prevent moisture problems, try these solutions after preventive measures are in place.

ü       Install a ground moisture barrier, which is a piece of heavy plastic sheeting (6 mil minimum) laid on the ground. Black heavy plastic film works well, but tough cross-linked polyethylene is even more durable. Secure the edges to the foundation walls 6” above the ground with polyurethane adhesive and/or mechanical fasteners.

ü       Overlap the ground moisture barrier seams by 12” and seal with polyurethane adhesive.

ü       Verify that clothes dryers and exhaust fans vent to the out­doors and not into crawl spaces or attics.

ü       Seal water leaks in the foundation.

ü       Seal water leaks in the roof.

ü       Remove unvented space heaters, a major source of mois­ture, from the home.

ü       Educate clients about ways of reducing home moisture that are under their control.

ü       Educate customers to avoid excessive watering around the home’s perimeter. Watering lawns and plants close to the house can dampen its foundation. In moist climates, keep shrubbery away from the foundation, to allow air circula­tion near the foundation.

ü       Insulate air-conditioning ducts to prevent summer con­densation.

More Costly Moisture Solutions

Follow these preventive measures before trying any of the solu­tions in the next section.

ü       Install or improve air barriers and vapor barriers to pre­vent air leakage and vapor diffusion from transporting moisture into building cavities. See page 457. 

ü       Add insulation to the walls, floor, and ceiling of a home to keep the indoor surfaces warmer and less prone to winter condensation. During cold weather, well-insulated homes can tolerate higher humidity without condensation than can poorly insulated homes.

ü       A sump pump is the most effective remedy when ground water continually seeps into a basement or crawl space and collects there as standing water. Persistent ground-water seepage may only be solved by connecting an interior perimeter drain to the sump. The sump cover must be openable, rigid, and must not interfere with drainage.

ü       Ventilate the home with drier outdoor air to dilute the more humid indoor air. Ventilation is only effective when the outdoor air is drier than the inside air, such as in win­ter. In summer, outdoor air may be more or less humid than indoor air depending on climate and whether the home is air conditioned.

Dehumidifiers and Air-Conditioners for Drying

As a last resort, remove moisture from indoor air by cooling the air to below its dew point with dehumidifiers in winter and air-conditioners in summer. Using air conditioners and dehumidifi­ers for drying a home is the very most expensive solution. Try all the moisture solutions discussed previously before resorting to a dehumidifier.

The dehumidifier should meet these specifications.

ü       Must be Energy Star or more efficient.

ü       Must have a fan-off option.

ü       Must retain automatic settings after power interruption.

ü       Must be rated for low temperature operation if located in a basement or crawl space.

When you install a dehumidifier, observe these requirements.

ü       Install the dehumidifier in a location that allows free air­flow around it.

ü       The dehumidifier should have automatic controls to limit energy and power.

ü       Make sure that the dehumidifier works and measure the relative humidity in the space before completing the installation.

ü       Drain the dehumidifiers collected water to a plumbing drain in a code-approved way.

ü       Give the homeowner the user guide, warranty informa­tion, and explain how to use the dehumidifier. Show the occupant how to clean or change the filter and how to clean the condensate drain.

1.5.3   Crawl Space Moisture and Safety Issues

Air, water vapor, liquid water, and pollutants move through soil and into crawl spaces and dirt-floor basements. Even if soil’s surface seems dry and airtight, the soil may allow a lot of water vapor and soil gases to enter a home.

Cover the ground with an airtight moisture barrier to prevent the movement of moisture and soil gases from the ground into the crawl space using these procedures.

ü       The crawl space should have an access hatch or door that is sized adequately for a worker or a resident to enter and exit.

ü       Remove biodegradable matter, such as wood and card­board, from the crawl space.

ü       Cover the ground completely with a ground moisture bar­rier such as 6-mil polyethylene where little or no foot traf­fic exists. Install reinforced or cross-linked polyethylene where the barrier will see foot traffic, such as when the crawl space is used for storage.

ü       The edges of the barrier should run at least 6” up the foun­dation walls and internal supporting structures. Fasten the barrier with wood strips, masonry fasteners, and sealant. Installers may also adhere the barrier with polyurethane adhesive or acoustical sealant to a clean and flat masonry surface.

ü       Seams must overlap at least 12 inches. Seal the edges and seams with urethane, acoustical sealant, butyl caulking, or construction tape to create an airtight seal between the crawl space and the ground underneath.

ü       To avoid trapping of moisture against wood surfaces, ground moisture barriers must not touch wood structural members, such as posts, mud sills, or floor joists.

1.5.4   Ground Moisture Source-Reduction

Observe the following specifications to avoid building deterio­ration from ground moisture. Finish the following tasks before air sealing the floor or installing underfloor insulation, with non-DOE funds or as allowed under DOE guidelines.

ü       Repair plumbing or sewer leaks.

ü       Solve all drainage problems, ground-water problems, wood-deterioration, and structural problems.

ü       Verify that the ground outside the home slopes away from the foundation or that water doesn’t puddle near the foun­dation.

ü       Install or repair rain gutters as necessary, and verify that downspouts discharge rainwater at least 3 feet away from the home.

ü       Verify that all combustion vents (chimneys), clothes-dryer vents, and exhaust fan vents are vented to outdoors and not into crawl spaces.

ü       Suggest a sump pump for crawl spaces or basements with a history of flooding. The sump pump should be located in an area where it collects water from the entire below-grade area and pumps it away from the foundation to daylight.

ü       Provide crawl-space ventilation which follows the require­ments of the IRC and SWS. See “Crawl Space Ventilation” on page 379.