[Greenbuilding] [BULK] Water Damage

[Lawrence Lile]

I'm mostly asking the question because I don't understand ice damming
very well.  Is it actually house heat, warming up the snow on the roof,
that causes ice to form and water to back up?  

I notice the metal roof makes a great solar collector, and on sunny days
the snow starts to melt and slide off.  If the snow melts at the top of
the roof, runs down, but stops at the snow fence, would this not cause
the ice dam phenomenon?  I am not sure.  The snow guard or fence, is a
metal bar installed horizontally on top of the standing seams, so there
is an inch gap below it that presumably would let water run out.  Roof
under the bar is an uninsulated, ventilated three foot wide eave, but
the house is insulated R60 full depth over the outside edge of the stud
walls, with a ventilated attic.  

After last winter, snow guards are going up all over the place around
here.  We had record snow and ice, so now that the horse is out of the
barn, so to speak, everybody is installing horse gates. 

 
 
Lawrence Lile, P.E., LEED AP

-----Original Message-----
From: Shawna Henderson [mailto:shawna at abridesign.com] 
Sent: Friday, April 13, 2007 12:30 PM
To: Lawrence Lile
Cc: Greenbuilding List
Subject: Re: [Greenbuilding] [BULK] Water Damage

Lawrence,

Snow guards are commonly installed on metal roofs in alpine areas to  
stop those killer chunks from killing (c)hunks...
if there is adequate insulation at the eaves, why would ice damming  
be any more of a problem with a snow guard than without?

Shawna Henderson
principal,
Abri Sustainable Design & Consulting
Nova Scotia, Canada