Measurement of Attic Temperatures and Cooling Energy Use in Vented and Sealed Attics in Las Vegas, Nevada

Abstract

Traditionally, building codes have required that attics of residential buildings be vented. The ventilation requirement varies between one square foot of net free ventilation area per 300square feet of attic floor area (1:300) to one square foot per 150 square feet (1:150). In cold climates, the primary purpose of attic ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow, and to vent moisture that moves from the conditioned space to the attic. In cooling dominated climates, the primary purpose of attic ventilation is to vent hot air, heated by solar gain on the roof, thus reducing the cooling load contribution from the roof. The magnitude of the roof cooling load contribution is often in the area of ten percent of the total cooling load for an occupied house. The need for attic ventilation in hot and hot-humid climates has recently come into question. It has been suggested that by moving the ceiling air barrier and thermal barrier to the plane of the roof, that better building airtightness can be more easily achieved, and that the elimination of heat gain to the attic air distribution ducts would more than offset the additional heat gain caused by not venting the attic. To investigate this further, both a computer modeling study and an experimental study in Las Vegas, Nevada were carried out. building science.com