Attic ventilation, moisture and hot air

About Attic Ventilation

How do you get the moist air in the winter and the hot air in the summer out of your attic? Answer: lots of attic vents. You want to allow the moist air to escape, especially in winter time when the interior of the attic is warmer than the outside temperature. The moisture (humidity) will condense at a cool temperature. The homes constructed today are tighter and therefore trap more moisture and heat in the attic if not vented adequately. Building standards have sewn up the homes that we live in tighter than a drum. Surprisingly, standards of ventilation adopted in the 1930s are still in use today! Most homes are woefully under ventilated.

Ventilation and roofing

Ventilation should be a major concern to anyone who is contemplating having their home re-roofed. It is common for the average household to produce from four to five pounds of water vapor per day. In poorly ventilated homes, this moisture has nowhere to go. So it forms condensation on the underside of the plywood sheeting of the roof, causing the plywood to expand, buckle and delaminate. This degrading plywood has an ill effect on the roofing, including reduced nail holding power, wind damage due to an uneven deck and stress cracks due to unstable decking materials.

In the summertime attic temperatures can reach 180 degrees and more. A proper attic vent system consists of an intake and an exhaust. A properly vented attic works like this; as warm air rises, it creates a slight suction at the intake vents. This relatively cooler air removes excess heat from the underside of the sheeting as it exits the exhaust. This cycle of heat exchange regulates the temperatures of the new shingle, saving your investment in roofing from becoming a cinder.

Choices are many in ventilation. The turbine ventilators are a good product, however they can require a lot of maintenance as they get older. Dormer vents are another option. They are simple and can be installed out of sight at the rear of the building. Continuance ridge vents is another option. Another option for removing hot air is a solar powered electric fan.

Your consideration of proper ventilation in your roof may be the difference between a successful, long lived roof or a complete failure in a very short period of time. When it comes to roof vents we say “The more the better”. If the ventilation is not doing the trick, you could try a portable or crawlspace dehumidifier to reduce moisture.


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