Air Flow Vents and Other Important Openings: Intro

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  1. Introduction, Article Index, and Basics (this page)
  2. Gable Vents
  3. Installing Roof Vents
  4. Peak Vents for Best Air Flow
  5. Airing a Dank Basement
  6. Expelling Moisture from Kitchen, Bath and Laundry
  7. An Exhaust Fan in a Ceiling
  8. A Clothes Drier Exhaust Duct

Some Basics

To an uninstructed eye, the only openings in a house are the windows and doors. In reality a substantial number of vented openings are deliberately cut into the roof, walls and basement of a well-constructed house to allow hot or moist air to escape and to draw cooler or drier air in from the outside.

In the basement, vents in the foundation walls keep condensation from forming on beams in the basement and inside the ground-floor walls. You can install small vents in the siding to keep moisture from accumulating be hind the wall sheathing and damaging wood and paint, although construction experts now recommend instead that interior walls be painted with glossy oil- base enamel to create a vapor barrier, followed by a coat of alkyd paint.

Attic venting is most important of all.

An unventilated attic is a year-round problem, even if it's insulated from the rest of the house. On hot summer days, attic temperatures can reach 135° to 150°, keeping the rest of the house hot long after sundown and putting a heavy—and expensive—load on air conditioners. In winter, when the house is heated but the attic is cold, condensation can form in side upper walls and ceilings adjacent to the attic, which can rot wood, insulation, paint and plaster.

A steady flow of air through the at tic, provided by a combination of the vents shown below, solves both problems by removing hot air in the summer and water vapor in the winter. Most of these vents are easily installed by cutting through the sheathing of a house in or near the roof. However, ridge and cupola vents call for the skill of a professional because of the amount of cutting that must be done.

If practical to install, vents in the soffit —the underside of the roof edge—are effective because they permit fresh air to enter the attic at a low level and rise, carrying heat or moisture up to be expelled through vents in the gables, the roof ridge or in the roof itself. While not all houses are suited to soffit venting, all re quire venting near the roof peak. For adequate air flow if there are no vapor barriers between the attic and the rest of the house, install 1 square foot of vent area for every 150 square feet of attic floor. If there are vapor barriers, in stall 1 square foot of vent area for every 300 square feet of attic floor. Half the vent area should be in the soffits, if possible, and the rest in the roof or gables.

A full range of roof vents. No single house would be fitted with all the openings in this drawing, which is meant as a general guide to the vents described here. Soffit vents fit into the wooden panel, or soffit, that covers the undersides of an eave. The single type is easier to install, but the full-length strip type is more effective; most effective of all is the fully vented soffit, with openings over the entire soffit area. Rectangular or triangular gable vents, often used in combination with soffit vents, are set into a wall near the peak of the roof and fastened to rafters, to vertical beams called studs and to bracing beams called headers that are par of the installation. Roof vents are set into the roof itself, between rafters, while cupola and ridge vents are set into the roof at its highest point, where the rafters meet the ridge beam.

Installing a single soffit vent. Make a cardboard template matching the part of the vent that will fit into the soft it. Locate a section of the soffit between two lookout beams—you can identify their positions by the exposed heads of the nails that fasten the soft it to the lookouts—and use the template to mark cutting lines for the vent hole. Drill a hole at the corners of the outline as starting points for a keyhole or saber saw, then cut along the lines. Screw the vent to the soffit.

Installing a fully vented soffit. (see graphic) For a fully vented soffit you must remove the existing soft it, which is held in place mainly by nails that are driven through it and into the lookouts, although it may also rest on a strip of molding at the top of the wall and against a fascia board at the edge of the roof. You may not have to remove the molding or the board to take the soffit out. Cut access holes between the lookouts, then pry the soffit from the lookouts with a hammer and chisel. Free the outer edge of the soffit first, so that you can swing it below the fascia board, then pull an entire soffit section off the top of the molding. Replace the section with a fully vented soffit, nailing each section to the lookouts.

Installing a Strip Vent

1. Marking the vent’s position. (see graphic) At each end of the soffit, make a mark about 3 inches in from the roof edge. Snap a chalk line between the two marks as the outer cutting line for the vent. Measuring in from the chalk line, make two additional marks at a distance equal to the width of the part of the vent that will fit into the soffit. Between the marks, snap a second chalk line.

2. Cutting the vent channel. (see graphic) Cut along the chalk lines between lookouts. Then make cuts between the lines to remove a soffit strip, leaving only the parts nailed to the lookouts. Cut into each once along the chalk lines and pry it loose with a chisel. Slip each vent section into the channel and nail it to the lookouts, If the lookouts prevent a good fit, chisel out enough to seat the vent.

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Updated: Sunday, August 14, 2011 21:19