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BRADISH
Member
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# Posted: 5 Apr 2022 16:40
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Hello all -
As I am in the final throws of purchasing the odds and ends to build my cabin I am having a bit of trouble finding good info online - so I figured I'd phone some friends.
I have a very standard 5/12 pitch truss, 20' wide by 32' long roofline. It will be topped with corrugated, painted, 29ga metal roofing. No valleys, no crazy lines.
I am going back and forth on whether or not I should put one course of Ice & Water Shield along the eave line of the roof.
I am in SouthCentral Alaska, so we see quite the grab bag of weather. Anwhere from -40F to 90F, up to 50ish MPH winds (had a wild 80+MPH wind storm two years ago, but thats rare), and obviously a fairly healthy amount of snow 4-6ft/yr.
I'm trying to decide if I need to use one pass of the GRACE Ice and Water Shield on along the eaves of the roof. For reference I will have eave flashing and facia flashing. Online I saw some negative issues with hot temps and metal roofs (the I&WS basically melted) although I suspect it won't be hot enough here for that to be an issue.
If I use the I&WS i will likely just put down 15 or 30lb paper for the remaining courses (I already have this on hand, donated from a friend).
If I skip the I&WS I would probably be inclined to use the savings to buy the GAF Tiger Paw synthetic underlayment. Seems like a very nice product.
I'm not purposely trying to be cheap here, but I don't want to throw good money after bad. Any thoughts from experience out there?
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BRADISH
Member
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# Posted: 5 Apr 2022 16:43
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For reference, I know that GRACE makes a 'high-temp' version of the Ice and Water Shield, but I don't think I actually need that, and also don't have any access to get it locally if I did need it.
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Bruces
Member
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# Posted: 5 Apr 2022 16:51
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I have a 12-12 pitch tin roof on my cabin ,I used ice and water under the entire roof .My thinking was that any condensation is taken care of instead of soaking my plywood and insulation .
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BRADISH
Member
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# Posted: 5 Apr 2022 16:59
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Quoting: Bruces I used ice and water under the entire roof
Wow. While I admire the 'bazooka' approach, it seems to me that this is overkill. (Yes, I understand a roof is a good place to go overkill.)
For perspective, is your roof ventilated?
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ICC
Member
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# Posted: 5 Apr 2022 17:09
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I would be careful about using the regular stuff under metal. It is not the air temperature that causes the trouble it is how hot the metal itself gets with direct sunshine on it. Does a car or truck body everget so hot that it could hurt to place your hand on it and leave it there a short time?
Since this is not built yet, have you bought the trusses yet? Were they spec'd to be built with a raised heel? (sometimes called an energy heel truss). They provide extra space at the wall for more insulation thickness without compressing batts and allow for easier ventilation. With sufficient insulation in that spot, the heat leakage that can cause ice dams to form can be eliminated. Then the ice&water shield is not as important. Here, we have been able to get code approval for a roof w/o I&WS if we use raised heel trusses and meet or exceed the zone required R-value in the ceiling.
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travellerw
Member
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# Posted: 5 Apr 2022 17:17
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I skipped the I&WS and went with synthetic underlayment.. No idea if it was the right decision yet as its only been 1 winter.
This was suggested by the company I bought everything from.
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BRADISH
Member
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# Posted: 5 Apr 2022 17:19
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Quoting: ICC Since this is not built yet, have you bought the trusses yet? Were they spec'd to be built with a raised heel? (sometimes called an energy heel truss).
Great question and points ICC.
The trusses have been paid for and built, just waiting on me to pick them up.
We went with a 12" energy heel on these. I am also planning on using the 4' black soffit insulation baffles between each truss to keep my insulation from being disturbed. (Photo attached)
No code to meet in my neck of the woods, but I want to do what is logical and sensible without throwing money away.
I am leaning towards the GAF Tiger Paw product across the entirety of the deck at the moment.
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BRADISH
Member
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# Posted: 5 Apr 2022 17:20
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Quoting: travellerw I skipped the I&WS and went with synthetic underlayment.. No idea if it was the right decision yet as its only been 1 winter. This was suggested by the company I bought everything from.
I love to hear it. What pitch was your roof?
You see a decent amount of snow too correct? (Can't keep everyone I haven't met straight in my head  )
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travellerw
Member
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# Posted: 5 Apr 2022 17:52
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Quoting: BRADISH I love to hear it. What pitch was your roof? You see a decent amount of snow too correct? (Can't keep everyone I haven't met straight in my head )
Ours is a gambrel roof.. So 2 hips and 2 eaves.
We got 4ft of snow this year, but it seems the gambrel roof really sheds the snow. I have never seen more than about 1ft of snow on it.
The company I bought it from said they never put anything but synthetic under the metal roofs. I asked about I&WS and they didn't think it was required on my roof. So I opted to save the money!
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Brettny
Member
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# Posted: 6 Apr 2022 07:22
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Quoting: Bruces have a 12-12 pitch tin roof on my cabin ,I used ice and water under the entire roof .My thinking was that any condensation is taken care of instead of soaking my plywood and insulation .
This is why you use proper metal roof underlayment. It's cheaper than the ice and water shield and made for the application.
And yes you should use the proper underlayment. Dont use tar paper.
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WILL1E
Moderator
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# Posted: 6 Apr 2022 08:08
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Travellerw and I pretty much have the same setup. My cabin is 16x32 with a gambrel roof. I did the Grace I&WS for the little section over the rafter tails and then 1-2ft up the first section of the gambrel. The rest of the roof is 30lb paper. My roof is also vented from the soffit to the peak using custom built baffles.
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Aklogcabin
Member
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# Posted: 6 Apr 2022 09:42
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If memory serves. 2 rows or 6' of ice n water shield is required from the soffit edge. Good luck on the build. Time to wrap the place up as fishing season approaches
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