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Q: Our 16-year-old painted redwood house has a terrible mildew problem, even during periods of bright sunshine. The inside of the house seems to sweat and the inside surfaces of the window frames are peeling. We would eventually like to have aluminum siding, but first we must solve the mildew problem. What do you suggest? 

A: You have probably checked the obvious sources of moisture such as a lack of kitchen and bath fans, and poor exterior landscaping that may allow rainwater to run into your basement and crawl space. Moisture rising from these areas is a common source of this problem. 

If you do not know the source of excessive moisture in the house, you should introduce some dry air from the outside. There are a number of air exchangers on the market that are designed for do-it-yourself installation and are reasonably priced. These units usually have a fan that moves fresh air in, over or through ducts that are heated by heated air from the interior of the house moving out through the same unit. 

This is not only a solution for excess interior moisture but an answer to super tight homes that suffer a lack of fresh breathing air. 

Q: Our house was built about 1925, with a cypress shingle roof installed on 1x4-inch wood strips, 8-inches on center. The attic has no ventilation or insulation. I would like to install a painted sheetmetal roof over the wood strips. My concern is condensation on the bottom of the sheetmetal. What is the best way to do this? 

A: Providing ventilation and a vapor barrier in the attic will control the moisture buildup and resulting attic condensation. You should also insulate the attic. Even though your house is located in a warm climate, insulation is cost-effective and will help make the house more comfortable. 

Check with your local utility company to determine the recommended amount of insulation for your attic. It is more practical to install insulation batts with an attached vapor barrier rather than using a separate vapor barrier. Place the batts on the attic floor between the joists with the vapor barrier facing toward the rooms below. 

You should also use at least two vent openings – to allow for air movement. Installing watertight vents in the sheetmetal roof may be difficult, so your best bet would probably be to use gable vents. A combination of gable and soffit vents would be even more effective. 

Since there will be a vapor barrier in the attic, the size of the vent openings can be less than it would be without a vapor barrier. Remember, the vent’s effective area is less than its actual opening. Screens or louvers can reduce airflow through a vent by as much as 50 percent. The effective area should be at least one-three-hundredth of the attic floor area. 

To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019. The most interesting questions will be answered in a future column.