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Where is All the Moisture in the Attic Coming From?

MARCO Moisture in the Attic
September 8, 2021 at 3:00 p.m.

By Cass Jacoby, RCS Reporter. 

It is important to ventilate to keep moisture out of the attic, but do you find yourself asking “How does all this water accumulate?” Read on to learn why moisture builds. 

We all know that ventilation systems are a necessity in attics; they let fresh air enter the attic and excess heat and moisture escape. Without proper ventilation, the roof system can prematurely age from excess moisture. Condensed water can soak attic insulation, cause mold, rot wood and compromise air quality. It's hard to read anything about ventilation without knowing up front that moisture is one of the biggest threats to a home, but you still might find yourself asking: Where is all this moisture coming from? 

 Moisture primarily comes from inside the home. Water vapor rises with warm air into the attic from the conditioned living area through light fixtures, duct work and other areas not properly sealed. Every day a family of four produces up to four gallons of water vapor from cooking, bathing,  laundry, breathing and perspiration. That’s 28 gallons of water vapor per week!  

With moisture coming from inside the house threatening the roof system, it's clear that a ventilation system is crucial to exhausting out excess moisture inside the attic, and to do that, the ventilation system needs to be balanced. Properly ventilated attics use the power of convection as well as prevailing winds to pull in cooler air at the bottom of the attic and push warm moist air out of the attic space at or near the ridge vent.  

When figuring out the ventilation needs for a roof it’s important to determine the Net Free Area (NFA), which is the space that allows for the air to pass through the vent. Visit marcoindustries.com/ventilation/steep-slope/calculator to determine your attics’ ventilation requirements. One square foot of NFA is needed for every 150 square feet of attic floor space. If a home has a vapor retarder installed, one square foot of NFA is needed for every 300 square feet of attic floor space. Just enter the attic floor space and the calculator will return the number of vents required for the following Python vents; Weather-Tite Rolled Ridge Vent, Weather-Tite FlexFit Ridge Vent, Python 65 Slant Back Vent or the Python 150 Round Vent. 

Learn more about MARCO Industries in their RoofersCoffeeShop® Directory or visit www.MarcoIndustries.com.



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