Mold-Free Remodels

Mold damage can be costly, but you'll have nothing to fear if you control moisture. Mold problems — and solutions — are rooted in the design, construction and operation of buildings. Applying several easy building practices and technologies, can keep your remodels mold-free. A new publication from the Partnership for Advancing Technology in Housing, "Moisture-Resistant H...

December 31, 2006


Sealing roof sheathing joints with bituminous adhesive tape before installing the underlayment will protect against water intrusion if the roofing materials are severely damaged.

Mold damage can be costly, but you'll have nothing to fear if you control moisture. Mold problems — and solutions — are rooted in the design, construction and operation of buildings. Applying several easy building practices and technologies, can keep your remodels mold-free.

A new publication from the Partnership for Advancing Technology in Housing, "Moisture-Resistant Homes," offers the following guidance to curb causes of mold.

Bulk Moisture

Roof Coverings: To protect against water intrusion from severe, wind-driven rain, apply bituminous adhesive tape to roof sheathing joints before installing the roof underlayment. This practice provides protection against water even if a roof is severely damaged. See PATH's Roofing Tech Set.

Window and Door Installation: Many window and door performance problems stem from incorrect installation because many contractors fail to follow the manufacturer's directions. If installers only check the packaging after the job is underway or completed, various components intended for moisture resistance — such as gaskets, flashing components, and clips — have been thrown away. Be sure you're properly informed, and update training for your installers as needed.

Wall Components Flashing: Window and deck ledger flashing are essential to prevent water damage. A variety of manufactured windowsill and door threshold flashing components such as pre-molded pan flashings are available in lieu of site-built flashing components.


Follow these steps, and all manufacturer's instructions for the best moisture-resistent window installation possible. Proper installation of window and deck ledger flashing is essential to prevent water damage.

Basement Insulation and Finishing: Install basement insulation and finishes so they dry to the interior. If you put low-permeability and continuous vapor retarders such as polyethylene sheeting or vinyl wallpaper on the interior of basement finishes, they may trap moisture vapor moving through the foundation. Unfaced fiberglass batt insulation and permeable paint finishes work well for basement walls that are framed and covered with gypsum wallboard — but pay attention to the details.

Because below-grade portions of the foundation wall must be able to dry to the interior, use semi-permeable rigid foam insulating sheathing products (for example, EPS or XPS). Product permeability levels vary by manufacturer, so check project specifications to ensure that the perm rating is greater than 1 perm for the requested thickness.

Site Planning: When you develop a site plan, show land and drainage patterns that convey surface waters away from the building site. For sites that provide natural drainage away from the building, the main challenge is elevating the foundation enough to maintain good drainage.

Proper grading to direct surface water and roof water runoff away from the home is one of the simplest and most important ways to avoid moisture problems. When possible, the finish grade should fall at least 6 inches over a distance of 10 feet from the building. The steeper this slope and the farther it ex-tends from the home, the better. Proper backfilling and compacting to prevent settlement are important to maintain good long-term drainage.

Very flat sites may require mounding the foundation pad and coordinating appropriate foundation elevations for proper drainage. On sloped sites, excavating and grading up-slope must sufficiently drain away from the building's perimeter and against the direction of the site's natural water flow.

Moisture Vapor

Below-grade foundation wall insulation and interior finishes must be installed correctly so moisture vapor can dry to the interior.

Moisture problems related to water vapor can be confusing because they have multiple causes. Seemingly unrelated decisions that you make for one building system will affect the migration of water vapor in a house. And, removing a cause will often correct or prevent a problem even in complicated scenarios where several factors are involved.

Building Materials: Protect building materials from exposure to the elements during storage and construction. Keep wood products such as structural panels and framing lumber under roof whenever possible; at least raise them off the ground, cover them with a waterproof tarp and secure the tarp carefully to protect materials from rain.

Inspect shipments of lumber and other framing materials upon delivery to confirm that they're moisture- and mold-free. This will be easier if you come to an agreement with your supplier when you order the materials. An agreement will be helpful in heading off a dispute about what to do with a product shipment that is wet or moldy.

Use a moisture meter to check the moisture content of building assemblies such as exterior walls. This is especially important if the wall assembly includes layers that slow the drying process once the wall is closed in. Depending on moisture exposure before and during construction, materials may store enough moisture to promote mold growth for some time after construction is complete.

Wooden materials generally will not support mold growth at a moisture content of 19 percent or less. Other materials within a wall assembly, such as insulation, also should be dry at the time of close-in.

If you're aiming to control drywall cracks and nail pops as well — a large source of callbacks due to moisture — the maximum moisture content of framing lumber at close-in will be lower. For most areas of the U.S., the moisture content of framing lumber should be no more than 10 to 15 percent at the time of close-in. However, the amount of shrinkage in dimensional lumber can be unpredictable. For additional information on the effects of moisture on framing lumber shrinkage and expansion, refer to The Wood Handbook, a product of the Forests Products Laboratory.

Ventilation: You can also combat moisture vapor at its source. When interior relative humidity levels become a concern, provide more whole-house and spot ventilation and add controls that automate ventilation.

Controls that enhance ventilation include humidistats, combination light/fan switches, timers with switches and combination light/fan switches with a programmable delay control for the fan.

Choose Energy Star qualified fans, and go for a sound level of 0.3 sones or less. The Energy Star qualification will ensure that the fan is energy efficient; the low sones will ensure that it isn't so noisy that the homeowner refuses to use it.

Author Information
Mike Blanford writes about better building practices on behalf of the Partnership for Advancing Technology in Housing ( PATH is administered by the U.S. Department of Housing and Urban Development. Learn more at



To learn more about combating moisture problems, see:

To download the entire guide, visit and search for Moisture-Resistant Homes.

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