Attic Insulation 6 - Attic Ventilation
In part 5 of this series on attic insulation, you learned how to prepare an attic for insulation. In this installment you'll learn about some of the common means of attic ventilation and then see how to install one of them.
Ventilating the Attic
Ventilation in the attic is of the utmost importance. If the attic isn't properly ventilated, moisture can be trapped, causing a great deal of deterioration in the insulation as well as in the wood structure. Insulation loses its R-value as it takes on moisture. Also, built-up heat is not vented in the summer and the attic becomes super-heated. Few attics in older homes are properly vented.
Soffit and Gable Vents
Soffit ventilation allows air to travel from outside the house into the rafters and out the gable-wall vents, or through ridge ventilation at the peak of the roof. Soffit ventilation plugs are screened and louvered so air can pass through but insects cannot. To install these vents, simply drill a hole with a hole saw between each rafter all the way around the outside roof overhang of the house. Push in the soffit ventilation plugs. On the gable wall, near the peak, you may want to install a sheet metal, louvered, screened vent to let the air out as it moves toward the top of the attic.
Another option is the continuous ridge vent, which is screened and available in 10-foot lengths. This is designed to be installed along the entire ridge of the house, allowing a passage for air but not for rain. These ridge vents can be difficult to retrofit in existing homes, but they are recommended in new construction and can be considered when reroofing.
The wind turbine is a very effective ventilation piece, also installed near the roof peak. The wind or air rising through the turbine turns the vanes in the turbine and gets the air moving near the top of the house, drawing moisture out.
Installing a Wind Turbine
To install a wind turbine, find a good location near the peak and between rafters. Remove enough of the roof shingles, tiles, gravel, or other roofing material down to the tar paper. You will need to expose an area slightly larger than the flange of the wind turbine. Place the flange in position, and mark the flange opening on the tar paper with a piece of chalk or colored pencil.
Drill a starter hole using a hole saw or a 1-inch drill bit or larger. Once the hole is started, you can use a reciprocating saw to finish cutting the entire flange area. Be certain the blade is long enough and suitable for cutting tar paper and sheathing. You may want to keep a few extra blades on hand, since the long, narrow reciprocating blade tends to break easily. Wear safety glasses or goggles when sawing.
Next, use a caulking gun to apply a generous amount of roofing asphalt cement on the outside perimeter of the opening to serve as a sealer. Now, you can nail the base of the turbine to the roof with roofing nails. Roll some tar paper over the flange to create a double seal, and carefully replace the shingles to cover the tar-papered flange. Be sure the turbine is properly interwoven with the shingles.
After that, simply install the wind turbine into the base, and you're in business with a very fine ventilator. Be sure you install the turbine properly, or there can be leaks. It is essential that the flange and the shingles are installed in the proper, overlapping fashion. Also, you may want to consider calling in a professional when installing a turbine in a flat or nearly-flat roof, since leaks are more likely to occur with these.
Put In Flexi-Vent Strips
Complete your preparation by attaching flexi-vent material (a waffle-like strip of plastic) between the rafters and against the roof sheathing. This is designed to allow air circulation to carry away moisture that would build up between the roof and the new insulation. Butt these strips right up next to each other and against the roof itself.
Now, you're done with attic ventilation and can move on to part 7, which covers insulating rafters.