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Insulation in a Tight Spot - What to do?

A few days ago, the friendly folks on this site helped me come up with a basic attic insulation plan for my house. However, there's a potential issue that I could use additional input on.

First, a quick description of the house/project:

- House is in Northern NJ (climate zone 6A)
- Built in the mid-1940s
- Stick construction
- Relatively simple gable roof currently covered with asphalt shingles that will probably need to be replaced in the next five years
- The roof stops at the edge of the house - there are no eaves/soffits, and thus no eave/soffit vents
- The attic is vented by two gable vents and three roof deck vents (there is no ridge vent)
- There is HVAC equipment in the attic
- The roof deck and gable ends will be sprayed with 4" of closed-cell foam, and the rafters encapsulated to eliminate thermal bridging, thus creating an unvented attic

The one potential issue is that at the edges of the house, the bedroom ceilings and roof basically meet. See attached picture to understand what I'm talking about.

The only foam guy I've had to my house for a quote said that he can't get foam down there because that would require using a long gun, and the foam cures so quickly that it would harden in such a gun. He said he'd build up what amount to very tiny foam kneewalls to air seal the space, and then do a normal foam job from there.

This approach makes me very nervous because that space will essentially be uninsulated and unvented. I'm not so worried about energy loss as I am about ice dams.

Do I have a valid reason to be concerned? If so, how would you handle this situation?


bedroom ceiling.jpg487.86 KB
Asked by Matt Culik
Posted Aug 11, 2014 2:48 PM ET


1 Answer

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The solution is to remove the drywall on the sloped ceiling so that the spray foam contractor has easy access to the roof sheathing.

Once the insulation work is complete, you can install new drywall and paint. Remember, drywall is cheap.

One point worth mentioning: you are planning to insulate your roof to about R-26. That is well below the minimum code requirements for roof R-value in your climate zone. (Although you inform us that northern New Jersey is in Climate Zone 6, it is, in fact, in Climate Zone 5.)

According to the 2009 International Residential Code, the minimum R-value for roofs in Climate Zone 5 is R-38. If you wanted to provide that much R-value with closed-cell spray foam, you would need to install 6 inches of foam. For more information on this issue, see It’s OK to Skimp On Insulation, Icynene Says.

Answered by Martin Holladay
Posted Aug 18, 2014 10:22 AM ET

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