Measured air flows across the ceiling in typical residential assemblies.

A laboratory for the study of residential attic performance under natural conditions has been constructed. In one of the test cells, with a flat ceiling, white shingles, and venting devices at the soffit and ridge, measurements were taken of air flow through the plane of the ceiling. A ceiling "hole" was constructed in the otherwise tight ceiling, consisting of a PVC tube, an anemometer and a direction sensor. Data were collected for a six-month period. The velocity data have been compared to the recorded values taken at the site for outdoor air temperature and wind (resolved to a north/south wind component). The results show that up to half of the variance in the air velocity measurements can be accounted for using these two variables. Of the two variables, outdoor air temperature is the more important. The air flow through the ceiling into the attic is considerably greater during the winter than during the summer months. There is a strong correlation between air pressure differences and air velocities through the ceiling hole.