A well ventilated attic is a very inexpensive way to reduce energy costs, prolong roof life and make your living space more comfortable. Research has proven that heat and moisture are an attic’s worst enemy. Yet a properly ventilated attic keeps a house cool and cuts down on air conditioning bills in the summer. In the winter it helps prevent the formation of ice dams and condensation. The best attic venting also helps to prolong the life of roof shingles.
Think of your attic as a buffer zone. Outside in the “real world” Mother Nature reigns in all her glory, with temperature swings and moody weather. Inside your home, you have a relatively constant temperature and humidity hopefully matching the comfort needs of the folks inside. The attic allows for a transition zone between the wild and the wonderful through the cooperation of your roof, radiant barrier, insulation, vapor barriers and ventilation.
Efficient attic ventilation systems allow a continuous flow of outside air through the attic, protecting the efficiency of the insulation and helping to lower temperatures in the living space in the warmer months. A properly ventilated attic can help reduce the load on your air conditioner by moving the superheated air out of your attic before it builds up and causes damage.
The FHA (Federal Housing Administration) recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space. For example, if your attic is 900 square feet, you need a total of 3 square feet of ventilation. This amount is generally divided equally between intake and exhaust ventilation (i.e., 1.5 feet of each), to insure proper air flow through the attic.
Proper attic ventilation consists of a balance between air intake (at your eaves or soffits) and air exhaust (at or near your roof ridge). Intake ventilation MUST be at least equal to exhaust ventilation. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation.
The obvious benefit of increased ventilation in the warmer months is a lower attic temperature, which can decrease cooling costs in the home. This is true regardless of how much insulation there is in the attic. In fact, attic insulation can actually cause increases in temperature in the home as the insulation holds the heat long after the sun is gone, continuing to transfer it slowly through the ceilings into your living space. Though we think of attic insulation as a barrier to the movement of heat, the oppressive heat of an under-ventilated attic can make your insulation a “fair weather” friend.
By far the best non-mechanical venting system is the combination of soffit vents and ridge vents. This system allows the natural flow of air along the roof rafters and the wind outside to create negative air pressure that draws air from the attic. This type of ventilation requires a specific roof design with an overhanging area at the lower edge of the roof called a soffit. Vents are installed into the underside of the soffit overhang to allow air to move into the attic.
To complement the soffit vents, another vent is installed at the peak of the roof, called a ridge vent. This is a screened replacement for the uppermost shingles bridging the peak of the roof, allowing air to flow in or out of the attic along the entire peak. The system is devilishly simple in function yet effective… warm air in the attic rises and exits through the ridge vents to be replaced by cooler air entering the soffit vents. Because the path of the cool air is along the underside of the roof deck, it provides uniform air movement and the best possible ventilating action. Continuous ridge vents are the most energy-efficient method of exchanging attic air.
Soffit vents come in many shapes and sizes. These are rectangular 16″x4″ vents.
An installed ridge vent blends with your roofline. From the inside, the slot cut for the ridge is clearly visible.