Tips for Good Attic Ventilation Roof inspection

Tips for Good Attic Ventilation

• Distribute soffit vents evenly around the attic, including corners. Place at least 50 percent of the vent area into soffits. Select vents with low air flow resistance.

• Install a ridge vent with low air flow resistance and good aerodynamics. Net free area (NFA) indicates resistance and is stamped on the vents. Higher numbers mean less resistance and better air flow. A standardized test has been developed, but not yet adopted by manufacturers. Until it is adopted, you may have to rely more on common sense than NFA. To judge the aerodynamics ask yourself these questions: Will air blow through the vent or flow over it? Will attic air flow easily through the filter? Can snow blow in?

• Install air chutes to protect soffit vents from blockage by insulation. They channel air flow along the underside of the roof sheathing and don't seem to reduce air flow significantly.

Baffles Improve Ridge Vents

Soffit Vents

soffit vents work well as inlets as well as outlets

There's less problem with rain and snow getting in, because soffit vents point downward. To get maximum protection, locate soffit vents as far out from the wall as possible. If rain or snow blow into the soffit, it's less likely to soak the insulation or drywall.

Soffit vents should always be installed whenever there are high vents. High vents, on ridges or gables, will pull air out of the attic. Without soffit vents, make-up air would be drawn through the ceiling, which increases heat loss and adds moisture to the attic.

Because of the importance of soffit vents, at least 50 percent of the vent area should be low on the roof.

More Research

For years, builders have discussed the merits of unvented roofs. Based on current information, venting attics seems to be a good idea. One of BRC's current research projects is looking into the question of unvented vaulted ceilings. Another study is looking into the merits of placing insulation just below the roof in a flat-ceiling attic. Including the attic within the conditioned space reduces heat loss from ducts, protects pipes from freezing, reclaims some storage and makes re-wiring much easier.