Ice and water roof membrane in Zone 5
Hi Everyone,
Building a one story barn/ranch home in Northern CT Zone 5.
Getting close to installing the roof in a few weeks and my framer
told me to get Ice and Water that is granular and not the IW that
is smooth. He said in the winter it hardens and becomes brittle.
On my previous builds I used Grace Ice and Water and it seemed
to be pretty sticky and I would do the entire roof. This roof is just a regular
12 pitch long roof which is simple with no dormers or complicated areas.
The sheathing will be 5 ply CDX 5/8 4×8 – roof trusses are 24 OC and I am 90% close cell spray foam will be sprayed under the roof decking. I like the idea of Grace on the entire roof as added insurance as I wonder if it is hard to find a leak when under the roof decking is sprayed foam.
Do some installers put the granular on the most outer 3 feet and then switch to smooth? In a climate where the winters are very cold with 40 pound snow loads, what would you do? I am also doing asphault – not metal.
Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
First, make sure your roofer is using the correct terminology. "Ice and Water Shield" is a trademarked product made by GCP Products, Inc. (formerly Grace). It comes only with a slightly embossed polyethylene (smooth) surface. It does not come with a granular surface.
Grace Ice&Water shield is designed for cold climates, and I have never heard of any problems with it becoming brittle and cracking. That may not be true for other brands, but I would still be surprised, considering the general construction of these products. You should check the specs on any underlayment product to make sure it is specified for your temperature range.
GCP claims that the polyethylene film on the surface prevents bonding between the asphalt shingles and the underlayment, unlike gravel-surfaced products. I can attest to the fact that gravel - surfaced products do bond to the shingles. Shingle removal for reroofing with these products is very difficult.
I do know that roofers often prefer to work with the gravel-surfaced products, feeling that the gravel gives them more traction. 12/12 roofs are pretty tough to walk on, and anything slippery makes that even more of a challenge. The plastic film on Grace products gives reasonably good traction in dry conditions but becomes a skating rink with any sort of moisture - rain, dew, frost, etc.
So the purpose of adhesive ice n water no matter what brand or surface composition is to seal around nails in case of ice dams. A repetitive thawing and freezing of snowpack in valleys or eves will allow water to infiltrate... normal capillary break of at the edge of the shingle isnt possible during ice dams and will allow water to travel uphill and come down underneath the shingles... with regular paper or synthetic paper it would leak into the house..
Use whatever brand that will maintain your warranty first and foremost and then secondly if it's not specified , use whatever brand or style your roofer wants to use