> -----Original Message-----
> From: J.A. Drew Diaz
> Sent: Wednesday, February 26, 2003 1:48 PM
> 
> 
> As I understand the problem the Ice dam alone isn't really 
> causing the problem, the problem is with capiallary action 
> which is wicking water back up under the shingles and 
> attacking the roof sheathing, 

A really impressive ice dam involves more than capillary action. They
can form to be a significant number of inches tall, trapping enough
water behind them that it literally submerges the entire face of shingle
units, allowing water to freely flow into the structure. Imagine trying
to hold water in a v-shaped trough with slate shingles as one of the
faces of the trough, the ice is the other face. Can't be done. Asphalt
3-tab shingles don't do too much better. 

And it gets really good and deep when it happens at the bottom of a
valley....

_________________________________________________________
Dan Becker,  Exec. Dir.,   "Help me, Mr. Wizard!  I don't 
Raleigh Historic            want to be here anymore!"
Districts Commission                 - Tooter the Turtle
[log in to unmask]  
919/890-3678

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