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Conditioned attic over porch?

foeller32 | Posted in General Questions on

I’m building a house in Northeast PA – Climate Zone 5.  The front of the house faces Northwest so there’s not a lot of sun exposure on the front-side roof.

I’m insulating the attic roofdeck with 8-10″ of closed-cell spray foam to create a conditioned attic space.  I’m not sure what to do with the open space above the front porch.  It seems like the most efficient option would be to add blocking and continue the plane of the front wall right up to the roof, and then spray foam the inside of the wall.  I’m concerned that this might cause ice dams over the front porch area.  I shouldn’t lose much heat through 8-10″ of spray foam, but even a small amount of heat loss has the potential to melt snow on the roof, which could then run down and re-freeze on the colder area above the porch.  Am I over-thinking things?

One other option would be to still spray-foam the entire roof deck all the way to the edge, and then also spray foam the ceiling of the porch. Though this seems like overkill if it’s not really necessary.

I suppose a final option would be to block off a “wall” in the attic as discussed in option #1, but still spray an inch or two of foam on the bottom section of the roof just to slow the movement of heat through that area.  So if warm water is running down the roof, it would be less likely to continue freezing in the bottom section.

What’s the best option?  I’m betting the first answer will be “it depends” 🙂

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Replies

  1. Expert Member
    Peter Yost | | #1

    Hi Foeller32 (always good to include your first name or a handy nickname...) -

    The best way to build a porch roof is to add it as an assembly AFTER you have completed the fully-insulated and air-sealed exterior wall to which the roof abuts. That makes your porch roof completely an exterior structure, unfed by conductive or convective heat loss from conditioned space and no ice dams.

    Peter

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