A Comparison of Sealed and Ventilated Attic Spaces: a Case Study of Residential Attic Design

Two attics were constructed as part of a building renovation project at the University of West Florida. The first attic is described as a traditional ventilated attic, with openings in the soffits and a small dormer vent on the roof. The second attic is described as a sealed attic (with no ventilation), and open-cell spray foam insulation installed on the underside of the roof deck. The study was undertaken to demonstrate hypothesized performance differences between attic types. Thermal and relative humidity sensors were installed to measure the condition of the air in the two attics spaces, and measurements were taken at 15 minute intervals. Measurements of relative humidity were later calculated as dew point and specific humidity. Similar studies are often conducted by comparison of attics in separate buildings under different use conditions. This project offers a unique opportunity to explore data collected from a single structure, and provides support for existing research on attic design in southern regions. The resultant data show significant differences in attic temperatures, with the sealed attic exhibiting a much more thermally stable pattern. There were also significant differences in attic dew points and specific humidity, although these differences appear to be much less pronounced. Data were analyzed using independent t-tests to establish significant differences between means. Overall, the sealed attic performed better than the ventilated attic, although dew point and specific humidity remain concerns.