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Moisture can be critical

“We have come a long way in the past 10-15 years in our understanding and reduction of gaseous contaminants, and the impact of furniture, wood products and building materials that, historically, out-gassed VOCs,” says David W. Wolbrink, vice president of research and development for the nation’s leading residential ventilation manufacturer.

“Excess moisture still exists in the home. In fact, the problem has grown more severe,” Wolbrink says.

It is essential to understand moisture in designing and operating a home in a way that preserves good indoor air quality.

Swings in the moisture level—in either direction—can lead to serious problems.

Ideally, indoor relative humidity should be held within a range of 30 to 50 percent. In hot humid climates that may be difficult, but relative humidity must absolutely never be permitted to be above 65%. In cold dry climates, relative humidity should be no lower than 20%.

Less than 30 percent relative humidity can cause wood to shrink, result in increased dust, cause respiratory, throat and skin irritations and create static electricity.

As the outside temperature drops, so does the recommended relative humidity inside the home, because during cold weather higher humidity will lead to excessive moisture and condensation, which can lead to mold and mildew.

Mold can grow on surfaces in any climate at humidity levels above 70 percent.

Water intrusion problems leading to mold buildup often are a result of faulty building envelope design and construction that permits water to enter the wall from inside or outside and trap it so the inside of the wall can’t dry out. Crawl spaces also are common sources of moisture buildup. More new homes than ever today are gabled, and intersecting rooflines can be another problem area if errors are made in roofing or flashing installation.

“Moisture—and resultant mold problems—are the subject of more current research than any other area of construction,” says a spokesperson for a U.S. ventilation manufacturer. “Ventilation won’t overcome the problems of bad design, but ventilation, coupled with good design, will create a very good indoor environment.”