Insulating an Attic With 2×6 Rafters
I live in NJ in an old 1930’s house. I’ve only got 2×6 rafters in the roof (which is interesting). My attic is currently uninsulated and there’s a lot of HVAC equipment and ducts up there. (Yes, I’m a poster child for disaster).
I’ve been looking a how to best insulate the roof. So far I seem the settling on add 6″ of closed spray foam to the rafters and create an unvented assembly . The rafters are 2″ x 6″ (actual not nominal) so I feel like close-cell spray is the only option.
I’ve read a lot of articles on the site (https://www.greenbuildingadvisor.com/article/a-new-look-at-conditioned-attics) and agree in general with the sentiment – don’t condition an attic however I have little to no choice.
So my question is – it’s 6″ of foam going to cause a problem as it will create an unvented roof assembly?
Exterior foam on the roof 4-6″ was an option but no one seems to want to entertain a job.As an aside, I read something on this site the other day where a contractor was explaining that the way he’s set up the company 1 week jobs are his target and he’s figured out ho to make money that way so that kind of makes sense in this area where I live — the volume of jobs means they need to be highly predictable.
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I've got the same 6" rafters in the one of the attics in my 1870 home. I've decided to put the new HVAC air handler up there. The Building Inspector is fine with me filling those rafters the best I can instead of trying to make code, so we're going with Closed Cell. Should be fine.
Thanks - I think so too. I hate to use this solution but what can one do?
The other alternative is to effectively make the rafters thicker.
The extra thickness isn't needed to hold up the roof, it only has to support the weight of the drywall and insulation so it can be relatively flimsy. There's a couple of ways of doing it, the best way depends on how much thickness you want to add what the existing construction is like.
You want to have at least a 1" air channel between the insulation and the underside of the roof. If you have the clearance I'd be looking to make the effective thickness about 13", that allows for the 1" air channel and R-49 insulation.