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Mildew and mold problems

QuestionWe are currently remodeling our 1947 vintage home in Austin, Texas. It is a pier and beam and we have been having a mildew/mold problem. I have cut some additional vents in the crawl space and am presently laying a 6 mil. poly liner and also insulating previously uninsulated walls. Do you think this will take care of our mildew/mold problem? Are there additional measures that we could try? After we add the insulation, should we also add a vapor barrier?

AnswerIt's hard to pinpoint a solution for a mold and mildew problem because you're really asking a two-part question. First, you need to address the mold and mildew. Second, you need to incorporate proper ventilation into your home to prevent further outbreaks.

If you don't quite understand how mold and mildew develop, let me give you a brief overview. Mildew and mold are part of the fungi group. Unlike plants, fungi do not produce their own food so they must derive their nutrients from the animals, plants, or decaying matter on which they live. In your case, the household paints are probably over ten years old and can no longer resist the fungi.

To get rid of mold and mildew requires a few chemicals and a lot of elbow grease! Wash your walls using a mixture of 1 cup trisodium phosphate (TSP), 1 quart liquid laundry bleach, and 3 quarts of warm water. When the surface is clean, rinse with fresh water. If TSP is not available in your area or its use is prohibited because of ground water regulations, your paint dealer can suggest an environmentally safe product.

Let the area dry for at least one week, depending on the time of year and the humidity, and then repaint using paint containing an anti-mildew additive. Again, your paint dealer can suggest an appropriate product.

In a high humidity climate, it is possible that mold/mildew can begin inside the stud cavities and actually permeate wallboard, appearing on the interior side of the wallboard. Unfortunately, wallboard removal and replacement won't really solve the problem because in a humid climate there's no way to actually dry out stud cavities. Depending on the level of damage, studs will need to be removed in this area or—in an extreme case—the house may need to be torn down.

Normally when mold and mildew appear in a home it's because the home was built so tight it doesn't have proper ventilation to breathe. In your case, you might have to install an air exchange unit or an electric ventilation fan on the roof or at each gable end. If there is excess moisture on the interior side of the windows, then you need to install a portable dehumidifier. It's important to check with your local building department to get requirements for your area to properly ventilate your particular structure.

Adding the 6 mil. poly liner in the crawl space will help with normal moisture but not with standing water from runoff or an underground spring. Eliminate this with a sump pump. However, redirecting water due to rain and snow runoff away from the home will prevent water from depositing in the crawl space. Make sure you use a black poly liner (not clear) as it will hold the moisture to the ground.

Mold and mildew result from excessive moisture, and ventilation's role is to ensure the removal of excessive moisture from the building. It's important to properly ventilate bathrooms, laundry rooms, and kitchens—these rooms are more prone to moisture than other rooms in a home. Another area of concern is an uninsulated AC duct, where the possibility for moisture is great.

Finally, when does the mildew appear—during the summer because of air conditioning, in the winter because of condensation, or both? As you plan your insulation and vapor barrier, consider the following:

  1. Where humidity is not a problem, install the vapor barrier on the warm side of the wall. During the winter, water vapor is blocked from penetrating the insulation and condensing on a cold outside surface.
  2. Where humidity is high in the summer and air conditioning is used, a vapor barrier is recommended on the exterior wall (warm side). During the winter, the interior vapor barrier prevents water vapor from penetrating the insulation and condensing on a cold surface. During the summer, the exterior vapor barrier can prevent water vapor from penetrating the insulation from the outside and condensing on a cold air conditioned surface on the inside of the wall.
  3. When installing the insulation, consider using a faceless insulation with a vapor barrier or foil back or Kraft-faced insulation. Alternatively, install a poly-wrapped encapsulated insulation, which is twice as resistant to moisture penetration as Kraft facing. It serves as a vapor barrier; however, in order for it to work, you need to face staple, i.e., staple the tabs across the face of the studs, the same as you would for the foil or Kraft-faced products. Kraft-face can be used as a vapor retarder and in some cases, e.g., humid areas such as the Gulf Coast, it is preferred due to its high perm (permeability) rating and its ability to let some of the moisture through.
  4. To block drafts that allow moisture vapor to pass through to the exterior wall and to help eliminate potentially harmful condensation build-up in wall cavities, consider some type of house wrap to prevent outside air from entering wall cavities. House wrap creates an envelope around the home and when properly installed, seals up sheathing seams and cracks around doors and windows to help stop drafts that would interrupt the interior cycle of energy efficiency.

To learn more about moisture and mold, go to Johns Manville and type in their search engine the following: "Technical Report by Larry Gelin Moisture and Mold Growth." The .pdf document brought up titled "Not in my Building; Moisture and Mold Growth and the Specification of Wallcovering" is very interesting.

The U.S. EPA, Office of Air and Radiation Indoor Environments Division (6609J) offers a document titled "A Brief Guide to Mold, Moisture, and Your Home." This guide provides information and guidance for homeowners and renters on how to clean up residential mold problems and how to prevent mold growth. For your .pdf copy, click here.

Copyright © 1999 & 2004 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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