Most experts say 1 square foot of ventilation is needed for every 300 square feet of attic. That said, if the house doesn't have a vapor barrier, you can benefit from more ventilation grilles. When done correctly, attic ventilation can reduce the chance of condensation in winter and summer. During the winter, the main cause of attic moisture problems is because warm humid air seeps into the attic space from inhabited areas and condenses on cold surfaces.
This can be intensified when lights, pipes, ventilation grilles, and other penetrations pierce the attic floor. Too often, mechanical ventilation ducts in bathrooms, kitchens, or laundry rooms deposit warm, humid air in the attic rather than outside the building envelope. But if you have proper ventilation, fresh, dry air comes in from outside to help warm, humid heat escape from the attic. In addition, proper ventilation can help keep the attic at an even temperature to prevent hot or cold spots and prevent ice dams from forming.
Proper attic ventilation helps address excess heat and moisture that could otherwise wreak havoc on your home. The accumulation of heat and moisture in an attic causes predictable but different problems in hot and cold climates; areas with hot summers and cold winters can suffer the effects of both. Attic ventilation draws air into the attic and allows air to escape from the attic. Because the roofs face the sun, they accumulate considerable heat in the warm season.
Attic ventilation provides an outlet for this heat gain and allows fresh air to enter the attic. The goal is to have an even flow of cold air from the outside through the attic and out through the exhaust, carrying with it the warm and humid air from the attic. In these climates, warm attic spaces are eliminated by installing a thermal barrier along the roof line, rather than the attic floor. A dry, well-ventilated attic prevents mold from forming both inside the attic and in the living areas below.
Ventless Attic Assemblies Unventilated attics are based on air-tight insulation installed at the bottom of the roof deck (i.e. combined attic assemblies) Modern residential design consists of elevations that can create multiple attic spaces within the same building. FHA recommends having 1 square foot of attic exhaust (both inlet and exhaust) per 300 square feet of attic space. Gable attic fans can move an enormous amount of air from the attic up to 5,000 cubic feet per minute (CFM).
Building Codes and Attic Assemblies Since 2004, the International Code Council (ICC) supplements to the International Residential Code (IRC) mean that non-ventilated attic assemblies have been accepted by building codes in residential, but not commercial applications. Attic ventilation can cool attics during the warm season and can minimize ice buildups in the cold season. As you turn up the heat and complain about the cold, all that hot humid air in your attic is impacted by the cold air in your attic. All homes with penthouses that meet the code will already have some attic ventilation, but it's always a good idea to expand the minimum ventilation requirements to keep your home in the best condition for the long term.
Because shingles and roof coverings bend, bend, and split when the attic gets too hot, attic ventilation maintains roof temperature at sustainable levels. I was told that the 2 attic vents are the only attic ventilation I have (the house has ventilated panels, all other soffit covers are ventilated). A roof ventilation system works by providing a continuous flow of air through the attic space, helping to remove overheated air and moisture from the attic and roof system and reducing the impact of temperature changes and humidity conditions both inside and outside the home. Poor insulation is usually the culprit, although if you enter the attic on a sunny winter day, the sun can heat the attic space more than your oven.