Check out the attached picture. This is what the builder built. tells the home owner “ice dams” are his problem, act of God etc. design is fine! Unreal!!
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I posted last summer on nearly an identical situation at a friend"s house. Hot air heat ducts run thru the attic as a retrofit to replace electric heat, including a metal chimney thru the roof. Plus, the rafters end at the top plate and thus no overhang or soffits for venting. The escaping heat on the north facing side of the roof would melt the snow, which would immediately refreeze in the gutters, filling them with ice, which would the run down and freeze on the siding. The consensus was to foam the roof sheathing which was done ($2700). No more melting snow, ice dams, and the upstairs is warm as toast.
Not to sound ignorant but if the air ducts are insulated, what is the harm in running them through the attic? We are having a house built that has soffits and a ridge-vent but the plan was to put the flexible insulation air-ducts for the 2nd story in the attic. Any information would be appreciated.
Thanks,
Jonathan
Vapor barrier in ceiling forms part of the building envelop and every time your run something up to or out of the attic you creating holes in your envelop. You would have to make sure that all holes are sealed very well. In addition, if you were to ever talk to a good HVAC designer, they would tell you to use rigid ducting (less friction). Keep all duct work and mechanical systems in the conditioned part of the building.
I'm no expert, I just know what I saw at my friend's house. Even though the ducts were supposedly insulated, they gave off a lot of heat and probably had a certain amount of leakage. Plus the main lines were close to the eaves and thus close to the underside of the roof deck and therefore heating it. The foam on the roof deck completely isolates it from the heat and closes off any air leakage.No ice dams even in this tough winter in Ct.
a la SIP panel
The problem is the heated air in the ducts is at 110 or so degrees and the insulation on the ducts would have to be very thick to stop the heating of the attic and making the snow on the roof melt early. The melted water collects at the gutter and freezes and the Ice dams start!
Thanks all. I suspected that was the reason.
Thanks again.
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