Attic Ventilation Mike Fulton, National Manager Technical Training and Compliance, O’Hagin LLC Attic ventilation is an important component in the creation of optimal environmental conditions in any residence or structure. Properly venting the attic space helps ensure a healthier environment and conserve energy. Attic ventilation may also reduce the build-up of ice dams in cold areas and play an important role in prolonging the life of the roof. Ventilation requires the free flow of air, which may be achieved using various methods and products. A proper ventilation system supports superior air movement by exhausting air from the upper vents (exhaust), causing a natural vacuum effect that draws air in through the lower vents or soffit (intake). Attic ventilation has been a standard in building construction and living envelope air quality for years. Although the language in the code has changed slightly over the years, the intent is still the same: to furnish adequate cross-ventilation to all rafter or truss spaces with ventilators located at or near the ridge and at the eave or cornice, creating a balanced intake and exhaust system. As building designs changed from gable end to hip roof designs, balance has many times been ignored, causing excessive heat build-up in the upper portion of the attic space. The results are two-fold. First, greater heat can significantly decrease the life of the roof coverings and underlayments. Second, higher attic temperatures mean greater heat transfer to the air conditioning ducts. Lowering attic temperatures decreases the radiant heat transfer not only to the living envelope, but to the AC ducts. The ducts, which may have only an R-3 to R-8 rating, are a pathway to increased air temperatures (by a few degrees) from the air handler to the last drop, thus reducing the efficiency of the AC system and providing that initial “blast of hot air” that gradually cools when the AC system kicks in. Air handlers installed in the attic have an even greater heat gain, adding to the increase in heat. In some cases, by decreasing attic temperatures through improved ventilation, homeowners have experienced between 10 to 20 percent decreases in utility costs.
Florida Building Code
Below are the current Building and Residential Ventilation Codes: 2017 Florida Building Code - Building, Sixth Edition SECTION 1203 VENTILATION 1203.2 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof framing members shall have cross ventilation for each separate space by ventilation openings 36
FLORIDA ROOFING | January 2020
protected against the entrance of rain and snow. Blocking and bridging shall be arranged so as not to interfere with the movement of air. An airspace of not less than 1 inch (25 mm) shall be provided between the insulation and the roof sheathing. The net free ventilating area shall be not less than 1/150 of the area of the space ventilated. Ventilators shall be installed in accordance with manufacturer’s installation instructions. Exception: The net free cross-ventilation area shall be permitted to be reduced to 1/300 provided both of the following conditions are met: 1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling. 2. At least 40 percent and not more than 50 percent of the required venting area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically, with the balance of the ventilation provided by eave or cornice vents. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted. 1203.2.1 Openings into attic. Exterior openings into the attic space of any building intended for human occupancy shall be protected to prevent the entry of birds, squirrels, rodents, snakes and other similar creatures. Openings for ventilation having a least dimension of not less than 1/16 inch (1.6 mm) and not more than 1/4 inch (6.4 mm) shall be permitted. Openings for ventilation having a least dimension larger than 1/4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of not less than 1/16 inch (1.6 mm) and not more than 1/4 inch (6.4 mm). Where combustion air is obtained from an attic area, it shall be in accordance with Chapter 7 of the Florida Building Code, Mechanical.
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