[Greenbuilding] [BULK] Water Damage

[Kidd, Peter]

When snow melts, it isn't snow "running" down :-) and your snow guard
isn't a water guard.  The problem is house heat that can be exacerbated
by sun heat.  John states more correctly that the problem is heat and
then an unheated portion, usually the eave.  Besides mechanical damage,
ice 'dams' dam up water, which on shedding not sealing roofs like
shingles can lead to leakage as the water backs up through the shingles.
You haven't had ice damming before, the new condition is the snow is
still there to continue to melt rather then having slid off once
slippery water formed.  As you describe your roof, I'd be surprised if
ice damming became a problem.  We've had two great ice damming years
here, a local building scientist (most fortuitously in support of a
contract) had a field day walking about photographing ice damming
conditions in all their variety.  Well insulated and to a lesser degree
ventilated roofs fare well here.

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of John
Messerschmidt
Sent: Friday, April 13, 2007 2:11 PM
To: 'Lawrence Lile'
Cc: 'Greenbuilding List'
Subject: Re: [Greenbuilding] [BULK] Water Damage

Ice damming happens because the snow melts on the under-insulated roof
and drains down to the overhang where it's colder and then freezes.  If
this happens over and over again, the water starts pooling and then
freezing, getting bigger and bigger until one day it all comes down,
taking your gutter and anything else in its path with it.  Ok, I'm being
a bit dramatic.


John



-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Lawrence
Lile
Sent: Friday, April 13, 2007 2:51 PM
To: Shawna Henderson
Cc: Greenbuilding List
Subject: Re: [Greenbuilding] [BULK] Water Damage

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


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