temperature between the attic and the outside create anair movement independent of the wind, and also a morepositive movement when there is wind. Turbine-typeventilators are also used to vent attic spaces (view C).Where there is a crawl space under the house orporch, ventilation is necessary to remove the moisturevapor rising from the soil. Such vapor may otherwisecondense on the wood below the floor and cause decay.As mentioned earlier, a permanent vapor barrier on thesoil of the crawl space greatly reduces the amount ofventilation required.Tight construction (including storm windows andstorm doors) and the use of humidifiers have createdpotential moisture problems that must be resolved byadequate ventilation and the proper use of vaporbarriers. Blocking of soffit vents with insulation, forexample, must be avoided because this can preventproper ventilation of attic spaces. Inadequate ventilationoften leads to moisture problems, resulting inunnecessary maintenance costs.Various styles of gable-end ventilators are available.Many are made with metal louvers and frames, whereasothers may be made of wood to more closely fit thestructural design. However, the most important factorsare to have properly sized ventilators and to locateventilators as close to the ridge as possible withoutaffecting appearance.Ridge vents require no special framing, only thedisruption of the top course of roofing and the removalof strips of sheathing. Snap chalk lines running parallelto the ridge, down at least 2 inches from the peak. Usinga linoleum cutter or a utility knife with a very stiff blade,cut through the rooting along the lines. Remove theroofing material and any roofing nails that remain. Setyour power saw to cut through just the sheathing (notinto the rafters) along the same lines. A carbide-tippedblade is best for this operation. Remove the sheathing.Nail the ridge vent over the slot you have created, usinggasketed roofing nails. Remember to use compatiblematerials. For example, aluminum nails should be usedwith aluminum vent material. Because the ridge ventalso covers the top of the roofing, be sure the nails arelong enough to penetrate into the rafters. Caulk theunderside of the vent before nailing.The openings for louvers and in-the-wall fans(fig. 5-31, view D) are quite similar. In fact, fans areusually covered with louvers. Louver slats should havea downward pitch of 45° to minimize water blowing in.As with soffit vents, a backing of corrosion-resistantscreen is needed to keep insects out. Ventilation fansmay be manual or thermostatically controlled.When installing a louver in an existing gable-endwall, disturb the siding, sheathing, or framing membersFigure 5-32.—Inlet vents.as little as possible. Locate the opening by drilling smallholes through the wall at each corner Snap chalk linesto establish the cuts made with a reciprocating saw. Cutback the siding to the width of the trim housing thelouver (or the louver-with-fan), but cut back thesheathing only to the dimensions of the fan housing. Boxin the rough opening itself with 2 by 4s and nail or screwthe sheathing to them. Flash and caulk a gable-endlouver as you would a door or a window.Small, well-distributed vents or continuous slots inthe soffit provide good inlet ventilation. These smalllouvered and screened vents (see fig. 5-32, view A) areeasily obtained and simple to install. Only small sectionsneed to be cut out of the soffit to install these vents,which can be sawed out before the soffit is installed. Itis better to use several small, well-distributed vents thana few large ones. Any blocking that might be requiredbetween rafters at the wall line should be installed toprovide an airway into the attic area.A continuous screened slot vent, which is oftendesirable, should be located near the outer edge of thesoffit near the fascia (fig. 5-32, view B). This locationminimizes the chance of snow entering. This type ofvent is also used on the overhang of flat roofs.5-26
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