A.Bill Rose, a researcher with the Building Research Council of the University of Illinois in Champaign, responds: Unfortunately, the best answer I can provide at this time is "I don’t know." I am ten years into a side-by-side comparison research test, and so far the performances of the fully vented roof and the unvented SIPs-equivalent roof appear to be about the same.

Our research has turned up other relevant information, though. In a vented cathedral ceiling (SIPs or not), with a continuous slot, say 11/2 inches deep, with openings top and bottom and the sun shining on the surface, air will be buoyed upward in the cavity. The air flow may be considerable. It has a distinct cooling effect on the lower part of...

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