A Vapor Barrier Can Prevent Moisture Buildup In Your Attic

HOME CLINIC: I'm having my attic insulated by a local contractor. When explaining the job to me, he referred to something called a vapor barrier. What is it and do I need one? - C.G., Bremerton

DEAR C.G.: Your contractor is right to recommend a vapor barrier. It is designed to prevent household-generated moisture from accumulating in your attic. Moisture can move through your ceiling material (i.e., sheetrock) and reduce the effectiveness of your insulation, stain your ceilings and even do structural damage. If you generate a lot of moisture in your home, a vapor barrier or "retarder" is probably a good idea.

If your attic is currently uninsulated, you can make use of insulation batts or rolls with foil or Kraft paper backing that will act as a vapor retarder. Place the insulation so the backing is between the insulation and the ceiling.

If you already have a small amount of insulation in the attic, the use of these moisture-barrier materials is difficult at best. The alternative is to apply a vapor-retardant paint on your ceilings. Ceilings in older homes with multiple layers of oil-based paint (in good condition) will usually perform as well as the vapor-retardant paint.

Keep in mind a major source of moisture in attics comes from household air that leaks into the attic. Vapor barriers alone do not stop air leakage. This air can carry large amounts of moisture. Your insulation contractor should look for and seal as many air leaks (bypasses) as possible. Common areas to seal are around the attic hatch, plumbing and electrical penetrations, light fixtures, exhaust fans, and where the house framing has created gaps and openings. Sealing these air leaks will also save energy and increase comfort levels by reducing heat loss in the winter.

Whether or not you opt for the vapor retarder, it's important to make sure your attic is adequately ventilated once you add insulation. Ventilation allows any moisture that reaches the attic to be carried to the outside. Recommended minimum ventilation is 1 square foot of "free vent area" for every 300 square feet of attic floor area. The "free vent area" is the effective opening that your particular vents provide after allowing for the blockage created by insect screens and louvers. Vents should be installed in both the lower and upper portion of the attic (approximately a 50-50 ratio). This will enhance ventilation by providing a flow-through pattern of air movement.

Household exhaust fans that vent to the outside (such as kitchen range hoods and bathroom fans) should be ducted to the outside, not just into the attic space. These ducts should be insulated when routed through ventilated attics in a cold climate. Use these fans to capture and remove moisture when cooking and bathing to control the indoor moisture levels at the source.

For a free publication on Reducing Moisture Problems and Attic and Crawlspace Ventilation call our toll-free Energy Hotline at 1-800-962-9731.

HOME CLINIC: A general contractor painted some new wooden bi-fold doors for me and it feels as if grains of sand had been added to the paint. The surface is very rough. What's the problem? Shouldn't a contractor be familiar with this? - C.E., Port Townsend

DEAR C.E.: The roughness you're feeling is wood "whiskers." It's caused by the grain in the wood rising when the surface is wetted. Sanding before the prime coat and between additional layers of paint will "cut" those whiskers. It also provides a good mechanical bond between the wood surface and layers of paint.

It's very important to take the time to sand the surface initially and between subsequent coats of paint. The best remedy for your bi-fold doors is to lightly sand them, then apply another coat of paint.

When sanding, match the coarseness of the paper to the size of the whiskers. Generally, fine-grain sandpaper will be sufficient. If the whiskers are especially thick, a medium paper may be necessary for the first sanding. Gradually work your way to a fine-grain paper. This will ensure the finished surface is smooth to the touch. Also be sure to sand in the direction of the grain rather than across it. Wrapping the sandpaper around a block of wood makes the job easier and keeps the wood surface uniform.

Home Clinic answers questions about home maintenance, repair and energy conservation. It is prepared by the Energy Extension Service, a division of the Washington State Energy Office. It appears Sundays in the Home/Real Estate section of The Times.