On Mon, 18 Aug 2008 06:40:02 +0100, Steve O'Hara-Smith
wrote:

Why ? What's so good about ventilating an attic rather than
using it as a heat trap.


It encourages the formation of ice dams in the winter, which causes snow melt to
back up under the shingles and leak into the decking, which rots the decking and
rafters, leading to premature roof failure.

Robert Scott
Ypsilanti, Michigan