Ventilated Attic Space

Don t avoid ventilating your attic for fear you re letting cold air into the house.

Ventilated attic space.

Therefore whole house fans are best suited for open well vented attics. 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. You can also contact your local municipality to check on building code in your area. The dormers and the attic space over the outside porch were sealed off from the rest of the attic by making a wall of plywood then insulating the wall with closed cell spf.

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. Most building codes require a ratio of 1 150 ventilation space to 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. 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.

Let s look at the following example. Jones has an attic space that measures 23 feet by 48 feet. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. Space attic vents evenly and mark the locations by driving nails up through the shingles photo 1.

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. 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. 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. Your actual living space is sealed and insulated at the attic floor the attic is outside this envelope.

This yields a total area of 1 104 square feet. Throughout the balance of this digest the terms attic and roof will and can be used interchangeably. If there are asphalt shingles on your roof the attic must be ventilated to comply with the terms of the manufacturer s warranty. Intake vents located at the lowest part of the roof under the eaves allow cool.

If your attic isn t ventilated well that humid moist air will build up in the attic space and can cause mold to grow.