Waltz Around Mold
(steps to avoid moisture and mold in the home)

Construction Design and Techniques

photo of outside view of home

These basic construction techniques can prevent or minimize moisture problems in the home.

Plumbingphoto of plumbing access panel

  1. Don’t put pipes of any kind in exterior walls.
  2. Do not use paper faced gypsum board in wet areas. Use cement board.
  3. Don’t put water heaters in attics or on the second floor. Put water heaters on a concrete slab—in a basement, in a garage or inside on a slab-on-grade near a drain with the floor sloping to the drain.
  4. Install a condensate drain under air handlers to collect water that drips from the coils. The best location for air handlers is inside the conditioned space on a slab near a drain, just like the water heater.
  5. Don’t put clothes washers on the second floor. Place the washer near a floor drain in the laundry area. Locate a water shut off for the clothes washer that can be accessed easily without having to move the clothes washer.
  6. Set dishwashers in a drain pan.
  7. Install access panels in order to check plumbing on showers and bathtubs.

Site Grading

  1. Drain/slope grade away from the building. Approximately 625 gallons of water drains from the roof of a 1,000 square foot house during a one-inch rain. Extend down spouts for several feet from the house, and slope the ground about 1 inch per foot away from the house to minimize the potential for roof water causing water problems in the home (North Dakota University Extension Service).
  2. Drain/slope driveways, decks, porches, patios away from the building.
  3. Direct gutter water away from the foundation using underground flexible pipe, clay tile or splash blocks.

Crawl Spaces

  1. If you build a crawl space, build it like a mini-basement. Insulate the perimeter with rigid insulation, don’t insulate between the floor joists. Install a sealed continuous ground cover. Don’t vent crawl spaces to the outside. Since crawl spaces communicate with the rest of the house, treat them as part of the house.
  2. If you live in an older house that has a vented crawl space, insulate between the floor joists. Make sure the crawl space does not have water draining into it. The soil should slope away from the exterior beams and the vent should be above ground level. Put vapor barriers on the ground in crawl spaces to prevent ground moisture from moving up and condensing on wood members or entering the home. Installing a vapor barrier on crawl space surfaces will only assist in the control of excess moisture vapor. It should be used in combination with an effective ventilation system.

Polyethylene Under Slabs

  1. Don’t put sand or pea gravel over polyethylene under a concrete slab. Always put the concrete in direct contact with the polyethylene. “Sand becomes a reservoir and pea gravel becomes a plenum negating the value of the polyethylene” (see sources listed above). Vapor barriers under concrete slabs resist the movement of moisture through the concrete and into the living areas.

Windows and Doors

  1. Design and build windows and doors under overhangs or eaves.
  2. Pan flash all openings. For slab-on-grades, depress the slab at door openings.
  3. Use double-glazed windows with vinyl frames that have thermal breaks.
  4. Make overhangs at least 18 inches wide.
  5. Window seals should slope down to allow any water that lands on them to drain off.

Roofs and Valleys

  1. The less pitch or slope on a roof, the more likely it will leak.
  2. Flash, seal and inspect areas regularly.
  3. Flashing and selection of moisture impermeable sidings are very important where walls emerge through roof lines.

Heating, Ventilation and Air Conditioning Systems and Ducts

  1. The HVAC System should be properly sized for the specific living space and maintained in a good operating condition.
  2. Don’t put air handlers in the garage or unconditioned attic.
  3. Test ducts for tightness (leaks less than 5% of the total air flow provided by air handler).
  4. Don’t use ductboard (internally insulated ducts).
  5. The best practice is to not put ducts in exterior walls, vented attics or vented crawl spaces.

Ventilation

  1. Add controlled mechanical ventilation to the house by having an outside air duct to return side of air handlers.
  2. Clothes dryer exhaust should always be vented to the outside.

    photo of external dryer vent exhaust

  3. Install fans in all bathrooms, toilet rooms, and laundry to vent them to the exterior.

    photo of bathroom exhaust fan

  4. Install kitchen range fan that is vented to the exterior. Do not install recirculating range fans.

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Housing and the Environment logo

Controlling Moisture to Control Mold Mini-Course developed by Janie L. Harris, M.Ed., CRS, Extension Housing and Environment Specialist, Texas AgriLife Extension Service, Texas A&M System, College Station, Texas.

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Last updated: 26 July, 2010

Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.