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MRA Addresses Household Humidity Myths

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Metal roofs perform well in all kinds of climates, even humid ones. Image courtesy of MRA member Drexel Metals.

By The Metal Roofing Alliance

Portland, OR - Summertime sweat happens, especially in areas of high humidity, but damp, moist home interiors are a sign of a potentially serious problem. Most of these problems can be traced to the roof or attic, but the exact causes can be the subject of misinformation or misconceptions.

In its mission to educate consumers and contractors about sound roofing design, especially in the case of metal systems, the Metal Roofing Alliance tackles some of these humidity myths below.

Myth #1: Moist indoor air is mostly caused by high outside humidity levels

Truth: While high humidity in the summer can certainly contribute to a home’s occupants feeling sticky and damp, moist interior air is mainly caused by typical household activities that generate condensation, along with lack of proper ventilation. That includes doing laundry, bathing, and cooking.

Today’s tightly built homes don’t breathe as much—which has weatherization and energy efficiency benefits—but also can cause condensation issues. Moisture that once seeped through the walls and windows of older homes now may get trapped or migrate to the attic, leading to problems like mold if not addressed through good ventilation.

Myth #2: An airtight attic is the best way to prevent dampness and increase energy efficiency

Truth: Proper ventilation in the attic space is vital to keep moist air from being trapped and insulation must be kept dry and fluffy to effectively do its job. Studies show that for every one percent increase in insulation moisture, there’s a loss of up to 2.5 percent of insulation R-value. Inadequate ventilation can cause higher energy bills in summer and can lead to ice dams in the winter.

To control attic moisture and condensation, roof ventilation should follow building science: soffit vents typically act as intake vents, with air exhausted out of the top. As a rule of thumb, ventilation should be a 50/50 split between intake (usually soffits) and exhaust (typically near the roof ridge) with enough vents to effectively balance the overall cubic feet of air space.

“It’s important to keep in mind that a quality metal roof will naturally minimize heat gain into the attic, and proper ventilation will allow any gained heat to be released, helping increase energy efficiency,” said Todd Miller, president of Isaiah Industries and MRA board member.

Myth #3: Metal roofs cause more condensation as compared to other options

Truth: Metal is non-porous, transmits heat and cold quickly, and is generally cool.  When moist, warmer air contacts the metal roof, it can cause condensation to be more noticeable.  However, when properly installed, metal roofs do not cause more interior moisture problems than any other roofing type.

Best practices include installing a metal roof over good quality decking and paying attention to details such as thermal break, which simply refers to allowing for enough airspace between the metal material and roof decking. Some metal roofing styles such as metal tiles have air space already incorporated as part of their design, helping prevent condensation.

Myth #4: It’s a good idea to allow interior moisture to escape through the ceiling.

Truth: While ventilation in the attic is essential, preventing moist air from escaping through a ceiling in the first place also is key. Consider using a vaper barrier between the ceiling and attic space to prevent moisture from rising.  Even using an oil-based paint for the ceiling can be a decent barrier. Seal all ceiling penetrations such as around canned lights. Use ceiling fans and run an A/C fan to circulate interior air. Make sure exhaust fans for bathrooms, kitchens and laundry areas are exhausting directly outdoors, not into the attic.

Myth #5: When it comes to exhausting indoor air, the more the better

Truth: As much as ventilation is critical, an imbalanced system can cause issues. Too much exhaust without enough intake will be starved for air, working backwards by drawing in unconditioned outside air and trapping moisture, potentially causing leaks and damp insulation. Likewise, too much intake may lead to cracked or collapsed ceilings in the event of severe winds and air pressure when air rushes in but can’t get out.

Myth #6: Unless I see a mold problem, it’s hard to tell if there’s too much moisture inside my house

Truth: Your contractor or roofing pro can check the moisture levels using a protimeter, a device that checks the moisture level in the wood and insulation. Up to 10 percent of moisture is typical, and anything above that is a concern for condensation problems and organic growth issues. Also check living spaces for mold and high moisture levels. Use your nose as a guide and look in closets, behind furniture, the basement, and crawlspaces if you suspect a problem.

Unified-Steel-MRA

Metal roofs comes in various styles. In Florida, California, Texas and other parts of the Southwest, metal tile systems offer the look of traditional Spanish tile, but with the performance characteristics of metal. Photo courtesy of MRA member Unified Steel.

About The Metal Roofing Alliance

MRA-logoRepresenting metal roofing manufacturers in the United States and Canada, the Metal Roofing Alliance (MRA) was formed in 1998 as a nonprofit organization to help educate consumers about the many benefits of metal roofs. The main objective of MRA is to increase awareness of the beauty, durability and money-saving advantages of quality metal roofs among homeowners, as well as to provide support for metal roofing businesses and contractors. For more information, visit metalroofing.com.

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