Ice Dams, Post-Build Fixes.

 
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Old 12-13-2016, 12:18 PM   #1
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Ice Dams, Post-Build Fixes.


Winter is just hitting my area and I've got a home I suspect may have ice dam issues soon. The home has 3" of 2# foam (+/- r-21) at roof deck. 3/4 of the home also has r-19 in cathedral ceiling rafters with some air space above to sprayfoam. There is no airflow or ridgevent being the roof rafters are locked foam from eave to ridge.

This home could use a new roof. I am considering metal and retrofitting some type of sheet good foam above a created airflow gap. Home is about an 8/12 pitch with straight peak.

Thoughts?

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Old 12-13-2016, 01:45 PM   #2
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Re: Ice Dams, Post-Build Fixes.


I'm not a roofer by any means, but what makes you think it will have ice dam issues? Is there previous damage indicating ice damming is a seasonal thing with the home?

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Old 12-13-2016, 02:02 PM   #3
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Re: Ice Dams, Post-Build Fixes.


Thanks for responding. The home is coming "online" now and we've had good snowfall. The home is showing snow melt with minor ice forming. I am concerned it will continue and potentially become an issue so just doing some preemptive brainstorming. The home is small, so snow raking it is an easy temporary solution, if it does show significant melt. Right now it's hard to tell.

Although melt appears to be uniform, the home has its furnace and on-demand water heater in he conditioned attic, which is adding to some heat trap above living area.

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Old 12-13-2016, 02:36 PM   #4
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Re: Ice Dams, Post-Build Fixes.


Adding an airspace, then foam, and a metal roof isn't going to make sense. Putting foam on the decking, then an airspace and a metal roof with ridge vent could help.

Heat cables are sometime used, but they have drawbacks.

Normal roofing would require ~2 rows of ice and water shield installed along the eaves to guard against ice dams getting water into the building.
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Old 12-13-2016, 02:41 PM   #5
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Re: Ice Dams, Post-Build Fixes.


Maybe examine the vent area in the attic (i.e. 1sqft vent: 300sqft attic floor area)? Obviously it sounds like the furnace and HW heater isn't helping.
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Old 12-13-2016, 02:50 PM   #6
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Re: Ice Dams, Post-Build Fixes.


My thought on a layer of foam over air space is isolating the heat from the roof covering. I think that would function better than just adding more insulation to the overall roof system, ie foam on top of decking. Although that would keep more heat inside. My concern is even with more insulation on roof, it'll still have heat transfer.

Anything that would be done would include eave to ridge venting.

HDAVIS, why do think it wouldn't do much?
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Old 12-13-2016, 02:52 PM   #7
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by CharlieDelta View Post
Maybe examine the vent area in the attic (i.e. 1sqft vent: 300sqft attic floor area)? Obviously it sounds like the furnace and HW heater isn't helping.
This is the primary issue with spray foamed roof decks, there is no venting; at least with this home.
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Old 12-13-2016, 04:35 PM   #8
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by META View Post
My thought on a layer of foam over air space is isolating the heat from the roof covering. I think that would function better than just adding more insulation to the overall roof system, ie foam on top of decking. Although that would keep more heat inside. My concern is even with more insulation on roof, it'll still have heat transfer.

Anything that would be done would include eave to ridge venting.

HDAVIS, why do think it wouldn't do much?
If you were adding anything, it would be foam first, then an air gap then roofing. The continuous foam will alleviate the thermobridging problems, then you'd have the venting to keep the roof surface colder.

If you put the venting first, you'd be wasting a lot of money on foam just to "solve" an ice damming problem, but you'd still be allowing heat to escape from the home at almost the same rate it currently is. You want to make the home more energy efficient as well as less prone to ice damming, not just the latter.
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Old 12-13-2016, 05:48 PM   #9
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by META View Post
My thought on a layer of foam over air space is isolating the heat from the roof covering. I think that would function better than just adding more insulation to the overall roof system, ie foam on top of decking. Although that would keep more heat inside. My concern is even with more insulation on roof, it'll still have heat transfer.

Anything that would be done would include eave to ridge venting.

HDAVIS, why do think it wouldn't do much?
You want the ventilation to keep the roof at outside air temp so you don't get uneven melting / freezing. If you put the metal on the foam and have the ventilation under the foam, you don't have effective ventilation of the roof system, and you don't get full value of the added insulation.

A lot of people will do a metal roof retrofit by just adding the sheet insulation over the deck, putting on ply or OSB on top, and installing a (thin) metal roof over that. I don't see a lot of ice dam problems on ones done that way.
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Old 12-13-2016, 07:15 PM   #10
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Re: Ice Dams, Post-Build Fixes.


I appreciate each of your input. I think the likelihood of noticeably increasing the thermal envelope on the roof end will be negligible in terms of what needs to be done to eliminate an ice dam. It sounds like I was over thinking this with considering air gap and foam, where a layer of decent foam could take care of it all together.
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Old 12-13-2016, 07:41 PM   #11
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Re: Ice Dams, Post-Build Fixes.


Air gap is easy to create with a cold roof. If you dont need any more insulation its pretty low cost as well. 2x2s over current sheathing and sheet over that. Other than increaseing height at fascia and rakes its not a huge retrofit.
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Old 12-13-2016, 08:02 PM   #12
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by PatChap View Post
Air gap is easy to create with a cold roof. If you dont need any more insulation its pretty low cost as well. 2x2s over current sheathing and sheet over that. Other than increaseing height at fascia and rakes its not a huge retrofit.
Right, wrong, or indifferent, this is the way I have always seen them done.
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Old 12-13-2016, 08:11 PM   #13
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by PatChap View Post
Air gap is easy to create with a cold roof. If you dont need any more insulation its pretty low cost as well. 2x2s over current sheathing and sheet over that. Other than increaseing height at fascia and rakes its not a huge retrofit.
I agree with that. He's in Michigan, so moving closer to the R-38 recommendation before putting the metal on wouldn't be a bad thing.
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Old 12-13-2016, 08:22 PM   #14
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Re: Ice Dams, Post-Build Fixes.


Here's the kicker, much of the roof system has about R-40 when including the R-19 bat fiberglass under the foam. I really think the roof needed higher R-values without the ventilation of excess heat. This thought is what had me concerned with just adding another layer of foam.
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Old 12-13-2016, 08:27 PM   #15
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by META View Post
Here's the kicker, much of the roof system has about R-40 when including the R-19 bat fiberglass under the foam. I really think the roof needed higher R-values without the ventilation of excess heat. This thought is what had me concerned with just adding another layer of foam.
If it's that good, you should be able to just switch over to a cold roof without adding any more insulation.
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Old 12-14-2016, 02:48 AM   #16
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Re: Ice Dams, Post-Build Fixes.


Is the heat that is creating the ice damns actually from the roof, or is it from the wall system/window/doors? even a basement heat leak? plumbing stack? R40 and no air flow shouldn't allow any ice damns....

Can you borrow a infrared camera?
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Old 12-14-2016, 10:35 AM   #17
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Re: Ice Dams, Post-Build Fixes.


The ice forming is fairly even along both eaves. No basement. It is about 20 degrees cooler today where yesterday and Monday were closer to just under freezing. I could be "freaking" out about nothing. I'll keep an eye on it and inform later.
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Old 12-14-2016, 01:27 PM   #18
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Re: Ice Dams, Post-Build Fixes.


If it aint broke...
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Old 12-14-2016, 05:04 PM   #19
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Re: Ice Dams, Post-Build Fixes.


Quote:
Originally Posted by Fouthgeneration View Post
Is the heat that is creating the ice damns actually from the roof, or is it from the wall system/window/doors? even a basement heat leak? plumbing stack? R40 and no air flow shouldn't allow any ice damns....

Can you borrow a infrared camera?
An R40 hot roof can still have ice damming. All of the rafters will allow heat to escape. Then again, sunlight can cause ice damming too, so it's a crap shoot sometimes.
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Old 12-14-2016, 05:33 PM   #20
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Re: Ice Dams, Post-Build Fixes.


24 winters fighting ice damming. There are things that can be done to help a little. Solving it ? No chance
6' of ice and water and pray for a mild winter

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