Attic Ventilation is very Important

Attic Ventilation

The detrimental conditions caused by excessive heat or moisture build-up in attics can often be prevented by providing adequate ventilation. As a minimum, it is generally recommended that there be at least one square foot of free vent area (actual unobstructed venting) for each 300 square feet of attic floor area. Additional provisions will be required for some house styles, due to locational factors, or if there isn't a suitable vapor retarder between the 1iving areas and attic. In an existing house, actual conditions can be the determining factor. If the attic is 20 degrees or more above the outside air temperature on a warm day, or there are any odors, condensation or signs of mold growth in the attic, then additional ventilation is probably required. The ideal arrangement in most cases is to provide intake vents at eave levels and exhaust vents at the roof ridge. In fact, recent changes in construction standards dictate balanced upper and lower attic area venting. This arrangement promotes natural air convection to draw in cooler air and exhaust hot, moist air. If the house design doesn't permit such venting, a combination of gable and roof vents that provide as much crossflow as possible can be used. Most newer vents will be labeled with the ventilation area they provide; if there is no listing assume that the free vent area is no more that 50% of the total vent area due to restrictions caused by louvers and screening. It is also important to make sure that vents are not blocked by insulation or other obstructions. With cathedral or vaulted ceilings or finished attic areas, it is especially important to make sure that there is adequate venting between the roof deck and any insulation or other materials. All roof vents should be left open year round; with proper insulation levels there should not be a concern with energy loss. While it is essential to provide adequate ventilation by passive means, in some cases forced venting may be advantageous. A wind or convection driven turbine ventilator is often added for a low cost boost to air flow. Electric attic exhaust fans, however, are often more effective at replacing the hot humid attic air with cool outside air. Thermostatic controls are provided for these units; in certain situations a humidistat may also be required. Normally these fans are set to activate at about 100 degrees, but they can be preset by the homeowner to any desired temperature. If an exhaust fan is used, the HouseMaster technical staff stresses that it is important to ensure that adequate intake air provisions are provided, otherwise the unit will not operate effectively Kitchen exhaust fans, laundry rooms and dryer vents, or bathroom exhaust fans ducted into the attic can add substantial amounts of moisture. The kitchen and dryer vent should never be ducted in this manner due to the added fire risk from the grease or lint that may be present. It is advised that bathrooms with showers or elevated moisture conditions also not be vented into the attic space. Whole house fans are also used for ventilation purposes, but these are primarily used to remove excess heat build-up from the living area. Consequently, adequate exhaust provisions from the attic area must be provided or the moist house air will aggravate conditions in the attic.