Roofing Article

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Energy Savings with Proper Attic Ventilation

Modern home construction methods result in better insulated and tighter homes. This can save the average homeowner money on energy bills and make the need for a well ventilated attic even more important.

Good Roof Ventilation Does Make A Difference

Attic ventilation is necessary to prevent moisture problems and heat build-up, as well as, reduce heating and cooling costs. The benefits of proper ventilation for the homeowner are a cooler attic in the summer, a dryer attic in the winter and structural protection of the home from moisture damage.

Summer Heat

In the summer, heat builds up in the attic space, which will cool at night if the attic is properly ventilated. However, if the attic is unventilated or ventilated incorrectly, the heat will build-up over a period of days and continue to increase the temperature inside the attic.¹

A 90-degree day with no attic ventilation can heat the roof sheath to 170 degrees or more. Heat radiating from the sheathing down to the attic floor can raise its temperature to as much as 140 degrees. Without adequate ventilation, today's heavier insulation will absorb and hold more heat built-up during the day and make the attic less likely to cool at night.

Overheated ceiling insulation conducts the heat through the ceiling down to the residents of the home. This causes the air conditioning system to operate for longer periods of time to reduce the heat.

Winter Moisture

The well-insulated attic also will hold moisture in the winter and moisture causes considerably more problems than excessive heat.

During the winter, air inside the home is warmer and carries more water vapor than the colder, dryer air into the attic. Cooking, laundry, showers and humidifiers add moisture to the air inside the home. Atmospheric pressure causes the vapor moisture to naturally migrate from high humidity air to low humidity air and as it moves into the attic, the moist air will condense into liquid on the cooler rafters, trusses and roof sheathing.

As the air gets colder, its ability to absorb moisture is reduced. And, as the insulation levels are increased in the ceiling the attic becomes colder and more likely to retain the moisture, which can damage the structure.

In some parts of the United States such as the Greater Chicago area, snow melting on a warm roof surface can cause an ice dam. The melting snow, usually near the ridge, runs down to the colder roof overhang and then refreeze into ice. Subsequently melting of the snow on the roof can accumulate as a pocket of water that eventually backs-up under the shingles to cause major damage. The results can be soaked insulation, stained sheet rock or peeling paint. In some cases, the build up of the ice weight can cause structural damage.

For more information on ventilation visit the Air Vent, Inc. website.

References:
1. Air Vent Inc.'s "Principles of Attic Ventilation"