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175 Strafford Ave. Suite 1, Wayne, PA 19087
VENTILATION
- INSULATION - CONDENSATION
Under Construction
A proper indoor humidity level must be maintained to prevent structural damage to the house and to assure comfort. Humidity levels that are too high may cause paint to blister, plywood to delaminate, wood to rot, roof shingles to buckle and insulation to lose it's effectiveness. When humidity levels are too low your nasal passages may dry out and your susceptibility to respiratory infections may increase.
Proper attic ventilation will prevent structural damage caused by moisture, increase the life of roofing materials, reduce energy consumption and enhance the comfort level of the rooms below the attic.
To determine if the existing ventilation is adequate, place a thermometer in the attic on a windless day to see if the temperature that is being maintained is more than 10 to 15 degrees warmer than the outside temperature. If it is then more ventilation is needed.
The requirements for proper attic ventilation is one (1) square foot of free vent for each 150 square feet of attic floor, if there is a good vapor barrier you need half that amount.
The best results for ventilating an attic area are obtained when the ventilation is uniformly distributed along the roof and is equally divided between high (exhaust) and low (intake) vents. The combination of the continuous soffit vent in the roof overhang and a continuous ridge vent at the peak of the roof gives the best overall distribution of air flow. The high-low location of the vents takes maximum advantage of thermal convection to move air through the attic. Power roof vents (attic fans) may be necessary in rare instances to insure adequate attic ventilation for winter moisture and summer heat control. Ideally an attic fan should have a thermostat, to reduce the extreme heat in the attic in the summer and a humidistat, to reduce the humidity levels in the attic in the winter.
Ridge vents should be installed along the full length of the roof and they should have a baffle (external or internal) to direct exterior air flow up and over the vent causing a negative pressure in the attic. This action will increase air flow out of the attic.
Flat roofs, roofs with shallow pitches and cathedral ceilings are another story. It can sometimes be difficult to ventilate the cavity between such roofs properly. if there are overhangs, continouos soffit vents can be employed. In some cases louvers can be installed in the fascia board. Another important point about these type roofs, since there is very little air space between the lower ceiling and the underside of the roof sheathing/structure, your insulation should be installed at least 1 1/2 inches thinner than the roof cavity. Otherwise, water condensed from moist air can be trapped in the insulation, making it useless, and allowing rot and mildew to get a hold.