I live in Wisconsin, and every winter there are features either on the TV news or in the paper about ice dams. They once again remind us about how they form, assuming we have short term, one year memories, and how we need to seal air leaks into our attics, improve attic ventilation (disputed by some), remove snow from eaves, yadda yadda yadda, to keep water from coming into our attics and then into our rooms. But they don’t seem to ever mention putting a membrane under the shingles when re-roofing. Such a simple concept, don’t you think? When you consider that the greater cost of a new roof is labor, why would you wish to skimp on materials? Since I’m sixty-one now, I don’t wish to replace my roof in my remaining lifetime (I hope for thirty years but will settle for twenty more — roof life, that is), so I’ve opted for the best shingles and the rubber underlayment at least three feet up the eaves and in all valleys, and totally over my add on sun room. No leaks — total peace. Since I’ve dealt with the attic, I can no longer compete in my neighborhood for the biggest icicles. Alas.
Edited 2/6/2009 10:17 pm ET by BARMIL
Replies
Funny and true.
I'm beginning to think that unless you have a SIP (or a foam sprayed underside) roof, then you will have ice dams, no matter how well you do everything else
I would like to think that there are enough talented people out there that you should be able to have a house with no ice dams.
Moe
Yeah...the talanted ones who have SIP roofs, or foam under the rafters......otherwise, it's just a losing battle.
I think even if you have NO air leakage into the attic, just the way the sun melts roof snow ends up making ice dams....
Here in NY, 30 miles north of NYC, the roofers (almost) always put down 1 coarse (3') or 2 coarses (6') of peel and stick membrane. Insane not to.
I use 2 courses of peel and stick. I also always build with raised heel trusses, or when stick built, rafters on a second plate on top of the ceiling joists. This has totally eliminated (my concerns of) ice damming.
Have a good day
CLiffy
our code requires Ice & Water extend 2' over the interior wall surface... so the minimum is a 3' course of I&W
You're discussing two different things:
Proper leak sealing, ventilation or insulation, etc. reduce the chances of ice dams occuring.
Ice and water shield reduces the chance that there will be damage when the ice dam occurs.
In a perfect world, ice and water shield would not be necessary. I see it used too often to try and correct a problem that would be better solved in other ways. And I often see it thrown at problems rather than figuring out what the true sorce of the problem is.
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You're spot-on with that analysis, Grant, and the key phrase you used is 'In a perfect world....'
I'm a strong believer in ventilated roofs but I still use I&W membrane because other factors than heat leaks can cause ice damming (solar heating, for example). IMO, in this climate any roof under 8 in 12 needs membrane at the eaves (min. 1 foot inside the exterior wall); any roof under 5 in 12 should have at least 3 feet of membrane coverage inside the exterior wall. 3 in 12 and below should have full coverage.
But they don't. Well, not enough of the new ones, and certainly not most of the older ones. Up here, there's a fair-sized business opportunity in roof shoveling. At least one roofing company now offers seasonal contracts guaranteeing to clear your roof everytime the snow accumulation becomes greater than 50 centimeters (about 1½ feet). I don't know what their rates are, but it sounds like a good way to keep some money coming in during the winter.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Can you get an ice dam with a metal roof?John
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Heres one.
http://forums.taunton.com/tp-breaktime/messages?msg=115501.1