Ice Dams, Post-Build Fixes.

 
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Old 12-15-2016, 07:18 AM   #21
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Re: Ice Dams, Post-Build Fixes.


Sorry I missed this earlier - as others stated you should not have an air gap between insulation & the best method is insulation directly on the roof sheathing - this helps eliminate air gaps & thermal breaks. The other item is you will always have icicles & even some ice that form even with a perfect roof - the just is just making sure you don't end up with something worse

I am not sure of your climate zone but per the codes do require at least an R20 (maybe up to 35 in your area) of an air impermeable insulation (foam qualifies - mostly see; http://thehtrc.com/2013/ice-dams-ici...c-condensation)

One quick final caveat is if you are in an area with 50 psf of snow or more, then you should have an air gap (aka cold roof) where you vent between the insulation & roofing as a best practice
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Old 12-15-2016, 06:05 PM   #22
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Re: Ice Dams, Post-Build Fixes.


I just want to clarify what the home has at the moment. Tell me if this is correct. 3" of 2#(is that considered closed cell?) spray foam sprayed to underside of roof sheathing in rafter bays ridge to eave. Then an additional R21 of fiberglass batts. You also said that in 3/4 of the house is the fiberglass. Does that mean that in 1/4 of the house it is just the spray foam? Also, what is the rafter size?
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Old 12-15-2016, 07:34 PM   #23
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Re: Ice Dams, Post-Build Fixes.


Home is 2# foam entire shell, walls and rafters (top of wall to ridge). Rafters are 2x6 however the ceiling also has cathedral created with sistered ceiling joists. R-19 batts are in all areas where sistered joists exist.

Weather has been much colder the last couple days, I think it's made all the difference as mich less melt occurring.
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Old 01-10-2017, 03:21 PM   #24
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Re: Ice Dams, Post-Build Fixes.


Photos or a site visit are key to solving an ice damming issue caused by an architectural and/or builder defect. We typically use a thermal imaging camera to best understand what is going on in those areas that you can't see. A cold roof, combined (sleepers) with foam is a good probable solution but a complex roof can hamper the ventilation. This model would provide additional insulation reducing energy and improving comfort while providing outstanding ventilation.

We have found that we need to get at least R30 to isolate the interior climate from the exterior (retrofits/rebuilds).

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