I looked at a roof today that is having leakage problems that have been on going for several years. I’m pretty sure there will be some rotten wood to fix under the shigles, which I think are about 20 years old, but the shingles themselves don’t look to be in bad shape and I couldn’t find any one place that looked suspicious for water infiltration.
One thing that did catch my attention though was the low pitch of the roof for it to have shingles on it in the first place. I’ll have to go back and get the exact mesurment, but i would guess it’s a rise / run of 2/12 or a 3/12.
What little bit of comon sense I have makes me think that water is being blown back up under the shingles during heavy wind and rain. What is the minimum pitch of a roof before shingles become ineffective and some other type of roofing, such as a tin roof should be used instead?
scott
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3/12 is min and in some climates, ther should be a double ply underlayment tarpaper under that. i wouldn't dream of putting shingles on a 2/12 without full ice and water shield under it, and a disclaimer on the warrantee.
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what exactly is an ice and water shield? on the few roof's i've shingled, all that was needed was tar paper, which even if done in 2 or 3 ply will have a bunch of nail holes in it when the shingles are laid.
think of it as duct tape for the roof! basically it's a tarpaper with glue on it, a little more complex but that's about what it is.
and on a hot day not nearly as fun to use as a roll of duct tape!
Ice and Water Shield is layered neoprene rubber with a granular surface and a self-stick backing. It adheres solidly to the roof deck and to itself, which forms a seal at the seams. It also self-seals around each nail driven through it.
It is to tarpaper what a "bulletproof" Kevlar vest is to a sweater vest.
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otherwise known as Bituthene, or 'bitch' because it is a 'bitch' to apply on a hort day, sticking to itself. It is a peel and stick membrane, not often with the granular surface, that backs up the shingles. It is often required in some jurisdictions from the eave up to three feet above the bearing exterior wall on roof, under shingles.Similar producrts such as Polyglas with the granular surface and a reinforcing weave withing, are also available WITH the granular surface that wouel nto require any shingles over them on a low slope roof
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thanks for the above info...
I have understood that it is used where ice damming can be a problem, but when you say "required in some jurisdictions", is that because one geographical area needs it more, or some jurisdictions just think it's important, and some don't?
to re-phrase my question... other than for ice dam protection, why would it need to go 3 feet up past the load bearing wall on a normally pitched roof?
Required in some places simply means that they have a written code requiring it, instead of just letting quality concerns and common sense dictate that it be used.
Burt - In a climate with a lot of cold and or snow, water will be slower running off the roof than say in Georgia, so it is more likely to be needed in NY or Michigan or Maine.
But 2/12 on the coast of Florida should probably have ice and water shield too, because wind can drive water up under the shingles very well.
opposed to this, a 2/12 in Tucson would make use of ice and water shield a wasteful redundancyI put it directly on the plywood. Sometimes I tarpaper over it.The reason for running it three feet above the exerior wall is that is whaer most ice damming happens
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am i correct in understanding that this completly replaces tar paper, instead of going on top of it?