Ventilated Attic Space

Space attic vents evenly and mark the locations by driving nails up through the shingles photo 1.

Ventilated attic space.

Intake vents located at the lowest part of the roof under the eaves allow cool. Don t avoid ventilating your attic for fear you re letting cold air into the house. Therefore whole house fans are best suited for open well vented attics. In cold climates the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow and to vent moisture that moves from the conditioned space to the attic ventilation acts to bypass the vapour barrier created by most roof.

Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. Follow photos 1 6 for the simple how to. Most building codes require a ratio of 1 150 ventilation space to attic floor space. If your attic isn t ventilated well that humid moist air will build up in the attic space and can cause mold to grow.

Your actual living space is sealed and insulated at the attic floor the attic is outside this envelope. Wear a dust mask while working in the attic and lay planks or plywood across rafters so you don t step though the drywall ceiling below. When determining how to insulate this attic space various assemblies were taken into consideration and a hybrid combination of vented and unvented attic space was planned. For this method to be most effective approximately equal amounts of ventilation should be placed at the soffits or eave level and at or near the top of the attic space.

Jones has an attic space that measures 23 feet by 48 feet. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space. Outside air enters the attic space through soffit or eave vents rises through the attic space as it warms and exits through vents that are positioned at or near the top. Let s look at the following example.

Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge. This yields a total area of 1 104 square feet. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. That said air resistance and interference such as vent grates reduces the area of true ventilation.

You can also contact your local municipality to check on building code in your area.