Article Scott Horstmann of Christian Brothers Roofing LLC
“Does attic ventilation really make a difference?” The answer is a resounding yes.
Improper ventilation can lead to or cause a number of negative outcomes in your home. Let’s take a look at what you want to avoid.
Excess humidity & precipitation– Precipitation is more likely to happen in the fall or early winter when humidity is high in attics that do not have proper air flow. If the outside temperature is extremely cold you may find ice forming on the bottom of the decking in the attic, when temperatures are higher you may find condensation on the bottom of the decking, and when the conditions are extreme as the condensation builds, it will actually drop water onto the attic floor causing the appearance of rain. If you want to check your own attic, look for these conditions on the north and east sides of the attic.
Warped or rotted decking – Moisture on the decking in the form of water or humidity can cause decking to warp, mold, rot and deteriorate causing a loss of structural integrity. At times these conditions will not be noticeable, but often you will see lift lines on the roof around the shape of the 4’ x 8’ sheets of decking. Lines along the decking edges indicate there is a ventilation problem.
Overheating – When the air is not flowing correctly, your attic can become overheated from sun exposure on the roof. This can make it more costly to air condition your living space, make your living space to feel warmer than it is, and your shingles to overheat and wear out much more quickly.
Ice dams – Ice dams are caused by excess heat. It is actually hot and cold that causes ice dams. When an attic is not properly ventilated and there is a snow load on the roof with the outside air temperature well below freezing, the sun can cause the attic temperature to rise above freezing. The attic heat builds and begins melting the snow load from the underneath side, turning it into water which flows down the roof under the snow toward the eaves. Once the water reaches the eaves where the temperature is sub-freezing it turns into ice and climbs back up the roof. The ice dam then will block the downward flow of melting snow and ice and allow water to push back up the roof under shingles and flashings, frequently into the attic space and onto the ceilings of your home.
Water Spots – Water spots don’t always mean that there is a roof leak. They do mean you have a problem. When the spots first show up following a “dry” snowstorm it is likely a ventilation issue. Ventilation will always equalize the ratio of intake versus exhaust. When the total amount of intake (soffit) ventilation is equal to or greater than the total amount of exhaust (roof) ventilation you have proper air flow. When the total combined amount of ventilation is adequate for the attic size and the total amount of intake ventilation is equal to or greater than the total amount of exhaust ventilation you have a properly ventilated attic.
This is just the beginning. Do some research of your own. Ask questions of those who are planning on doing work around your home to be sure they really know how to design a ventilation system.
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