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IMPROVEMENTS : Well-Placed Vents Top the List of Attic Upkeep

July 31, 1993|from Associated Press

A well-ventilated attic is important to keep a house cool in the summer and free of moisture damage year-round.

Ventilation is especially needed in unused attics where insulation has been increased to keep heat from leaking out of the rooms below in winter.

Because warm air rises, vents are placed low on the rooftop to let in fresh air, and along the ridge of the roof or in the gables to let the warm air escape.

The milder the climate, the more effective ventilation is at keeping your attic dry in winter and cool in the summer.

Building codes generally require a ventilation area equal to at least one square foot of open ventilation area for every 300 square feet of attic floor area. This is split evenly between vents in the low soffits--the wood lining under the lower edge of the roof--and high ridge vents at the peak of the roof. Instead of ridge vents, the vents may be installed in the gables in the side walls near or at where the roof peaks. Before you proceed, check with your local building department to make sure your plan is up to code.

Fan-driven vents are sometimes used in attics, but they create noise, may fail prematurely and are generally no more effective than properly installed non-mechanical vents. But don't confuse them with whole-house fans which, when installed in the floor of the attic, can be used quite effectively to help cool your home in summer. However, if you install a whole-house fan, you may have to increase the amount of attic ventilation, because the fan will exhaust much more air than a non-mechanical moisture ventilation system.

Roofing suppliers sell a variety of soffit vents: individual units and plugs, continuous strips or perforated soffit boards.

To install an individual soffit vent unit, make a template of the side of the vent that will go into the soffit. Trace its outline on the soffit between two rafter ends (look for the heads of the nails attaching the soffit to the rafter ends.) Drill starting holes in the corners of the outline. Then use a saber saw or keyhole saw to cut a hole. Screw the vent in place. The same technique can be used to install a continuous vent.

To install vent plugs, drill a hole slightly smaller than each plug in the soffit between each pair of rafters. Push the plugs in place.

With any type of soffit vent, install special foam baffles inside the attic between the ceiling joists to keep insulation from covering the vents and to prevent cold air from moving under the insulation.

To install a prefabricated, continuous ridge vent, cut a two-inch-wide gap along the peak. Snap chalk lines to mark cut lines on both sides of the ridge. Use a knife to cut through the shingles and roofing felt. Cut through the sheathing with a circular saw set to the proper depth. Be sure you don't cut into the rafters, the beams on which the roof is set. Caulk the bottom of the vent and nail it into place with gasketed roofing nails.

To install a gable vent, mark the house siding to position the vent opening, which should be one-quarter inch larger than the vent dimensions (excluding flanges.) Following the marks, use a circular saw to cut the opening through the siding and sheathing. Cut the siding far enough back from the edges of the hole to accept vent flanges and trim.

In the attic, cut any obstructing stud 1 1/2 inches above and below the opening. Frame the opening with 2-by-4 blocking, vertically and horizontally, large enough to house the vent. From the outside, push the vent into the hole until the flanges fit against the sheathing. Nail through the flanges and sheathing into the blocking. Cover the flanges with wood trim and caulk between the trim and the siding.

For a triangular vent, measure the outside of the house, as high on the gable as possible, to be sure that the vent will fit between the gable trim. In the attic, mark the position of the vent opening on the wall and drill holes through the wall to indicate where to cut on the outside without cutting into rafters. Cut any obstructing stud 1 1/2 inches below the opening. Frame the opening with horizontal 2-by-4 blocking. Then install the vent from the outside as described for rectangular vents.

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