How to Build a Mold-Resistant Home or Commercial Building

April 2005

Mold infestation in a new home or commercial building is common. The mold problem can cause severe health problems for occupants as well as substantially reduce the fair market value of the structure because moldy homes and buildings are now more difficult to sell or rent.

To build a mold-safe house or commercial building, follow these 20 mold prevention recommendations from Phillip Fry, Certified Mold Inspector, Certified Mold Remediator and author of the mold advice book, Do-It-Best-Yourself Mold Prevention, Inspection, Testing, and Remediation.
  1. Prior to blueprint drafting, obtain the advice and suggestions of a mold prevention consultant to include the most effective water intrusion and mold prevention strategies in building design, selection of building materials, and construction techniques. "The key to mold control is moisture control,” advises the U.S. Environmental Protection Agency.
  2. Make sure that the building lot and its landscaping grading are downward and away from the building to keep rain and surface water from entering the building foundations, basement walls, concrete floors and crawl space areas.
  3. Install a thick, high quality moisture barrier (with no holes from negligent installation) beneath any concrete floor slab or basement concrete floor to stop water from wicking up from the ground into the concrete, and thus into flooring materials and walls resting on the wet concrete.

    Do not use regular plastic sheeting as a moisture barrier because such sheeting is easily damaged in installation, and it usually suffers physical degradation over time—thus allowing water penetration into the concrete.
  4. Add adequate amounts of top-quality waterproofing compound into the concrete mix to transform the entire concrete floor or slab into an effective water barrier. Also, thoroughly waterproof the exterior of basement walls and of the building foundations.
  5. Dry thoroughly (30 days) the concrete floors and concrete/masonry walls prior to adding wood building components. New concrete holds thousands of pounds of water. Most of this water usually dries to the inside of the house or building if the wood building components are installed prior to complete concrete drying, according to the Nova Scotia (Canada) Department of Energy.
  6. Do not install plumbing supply lines into concrete slabs or floors, wherein the lines usually degrade and start leaking in 20 years or less. Hire the most capable plumber to install the best quality plumbing lines, fittings and equipment.

    Concentrate all plumbing lines and sewer drain lines in as few areas as possible, with large, easy access panels for the monitoring, maintenance and repair of plumbing components.
  7. Minimize the potential for water damage from frozen, broken pipes by insulating water supply lines (in the attic, crawlspaces, garage and exterior walls), protecting exposed outdoor faucets and sealing gaps in exterior walls.
  8. Use a hidden moisture meter to scan the ceilings, walls and floors of all plumbing areas for water leaks prior to building occupancy, and on a regular basis thereafter.
  9. Use steel framing components instead of wood, which is delicious food for mold growth, to build the walls, second floor, attic and roof of the building. Although steel framing is a little more expensive than wood, it is very affordable in the long term, especially in consideration of steel’s water damage and mold prevention qualities, as well as fire resistance.
  10. Alternatively, build the walls out of poured concrete, concrete blocks or insulated concrete building components. Use adequate amounts of waterproofing compound in both the concrete and in cement stucco interior and exterior finishes.

    Build weep holes into the exterior masonry walls. Weep holes are openings at the foundation level of a brick or concrete block wall that allow moisture to escape from behind and inside the wall. Do not close or block these openings.
  11. If the owner or builder uses any wood timbers, plywood, plywood substitutes, drywall, plasterboard and ceiling tiles, pre-inspect such cellulose-based materials for mold growth and mold stains prior to their use. Remove the mold completely from the materials or return the materials to the supplier, and replace with mold-free materials. Use a moisture meter to scan all wood for moisture content, which should not significantly exceed 16 percent to 17 percent.

    Cellulose is the main substance in the cell walls of plants (and thus of wood from trees), and it is used in the manufacture of the paper backing of insulation, artificial fibers (for example, for carpeting and padding), and many building materials such as drywall, plasterboard and plywood substitutes.
  12. In addition, spray all cellulose-based building material surfaces with at least two wet sprayings of an EPA-registered fungicide, followed with at least one coating of an EPA-registered protective fungicidal coating. Allow the surfaces to dry after each spray application.
  13. Install a high-quality rubber water barrier beneath the roof shingles or tiles to keep rain from entering the building should there be degradation of, or damage to, the shingles or tiles. Install gutters (with leaf-catching screens) that lead to in-ground pipes that take rainwater away from the house.
  14. During construction, store all mold-vulnerable, on-site building materials off the ground and beneath waterproof tarps or plastic sheeting to protect the materials against rain, and thus against mold growth.
  15. During rain and as a precaution at the end of each construction day, cover the entire building with waterproof tarps or plastic sheeting to keep rain off of the building until the roof has been shingled, and the siding and windows have been installed.
  16. Prevent construction defects that allow water entry into the home or building by carefully monitoring the day-to-day construction of the structure. A construction-savvy owner, a trained employee of the building’s architect or an independent physical engineer or home inspector should do this important construction quality control monitoring. Construction defects are an important cause of mold infestation.
  17. Design the heating/ventilating/air conditioning system to have in its return air duct a built-in mass media (6 inches or thicker), replaceable HEPA filter or a top-rated electronic air cleaner to remove continually airborne mold spores from the circulating air.
  18. Install a programmable dehumidifier into the HVAC to reduce indoor humidity to a mold-discouraging 30 percent to 40 percent. Do not install a moisture-increasing humidifier. Install a humidistat-controlled exhaust fan in the attic and any crawl space area to help keep the humidity level low in those areas. Install exhaust fans that vent directly outdoors in the bathrooms and kitchen.
  19. Do not use wall-to-wall carpeting because carpeting and padding are great mold food and a great place for mold growth, viruses, bacteria and dust mites to hide and to multiply. Instead, for concrete floors, use ceramic tile set in cement containing a waterproofing compound. Use colored cement with waterproofing as the tile grout. For wood floors, install vinyl tile or linoleum. Use washable area rugs for comfort and beauty.
  20. During construction and also upon completion prior to sale, rental and occupancy, the building should be inspected and mold tested all-around for mold problems by a Certified Mold Inspector, or with do-it-yourself mold test kits.

For more information about mold prevention, visit one of the following Web sites:
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