Thoughts on barrier for attic insulation

[birds.of.a.feather]

Have some questions around attic insulation, we've got spray foam applied along the roof deck, which creates a decent thermal barrier, but the way it's set up, there's no actual air barrier separating the foam layer from the rest of the attic space now thing is, we're planning to run a ventilating dehumidifier up there to keep moisture under control, but does the open connection between the foam and attic space defeat the purpose and will the setup still count as a conditioned attic? or am I just letting the dehumidifier fight an uphill battle?
Appreciate your thoughts please, been grinding with the boys on this one for a while now

 

[JRobert Oppenheimer]

If the attic is open to the foam layer and you're treating it with a dehumidifier, then yeah, it basically be comes a semi-conditioned space. SEAL any air leaks that's it you'll still get good results.

 

[DeCorps]

Have some questions around attic insulation, we've got spray foam applied along the roof deck, which creates a decent thermal barrier, but the way it's set up, there's no actual air barrier separating the foam layer from the rest of the attic space now thing is, we're planning to run a ventilating dehumidifier up there to keep moisture under control, but does the open connection between the foam and attic space defeat the purpose and will the setup still count as a conditioned attic? or am I just letting the dehumidifier fight an uphill battle?
Appreciate your thoughts please, been grinding with the boys on this one for a while now

Most "conditioned attics" with spray foam aren't truly conditioned, they're just poorly sealed crawlspaces people hope work.

In your case, without a proper air barrier, that dehumidifier's gonna work overtime. You're basically trying to control open space, I'd seriously look into sealing things properly before running equipment nonstop.

 

[syllabus900]

I agree with @DeCorps there. From what I've read, for it to count as a conditioned attic, you need a continuous air barrier to fully separate it from outside air and unconditioned zones. Without that, your dehumidifier might be working overtime. Did you seal around penetrations like vents and framing gaps? Also, are you using open-cell or closed-cell foam? That can affect moisture movement too.

 

[Tir_McDohl]

Spray foam usually makes the attic conditioned if sealed right, but if it's open to the attic space, it sucks... literally. You're better off ducting in a little conditioned air (~20–50 cfm per 1,000 sf) or adding a small exhaust near the ridge to push out humidity. Otherwise your dehumidifier is just spinning wheels.

 

[Millirack]

Consider putting in a drywall ceiling or a vapor barrier under the foam.

 

[glass3s9uy]

Have some questions around attic insulation, we've got spray foam applied along the roof deck, which creates a decent thermal barrier, but the way it's set up, there's no actual air barrier separating the foam layer from the rest of the attic space now thing is, we're planning to run a ventilating dehumidifier up there to keep moisture under control, but does the open connection between the foam and attic space defeat the purpose and will the setup still count as a conditioned attic? or am I just letting the dehumidifier fight an uphill battle?
Appreciate your thoughts please, been grinding with the boys on this one for a while now

yeah, that dehumidifier will absolutely be fighting a losing battle. The whole point of a conditioned attic is that it's a sealed space. Without a proper air barrier, you're just going to be paying to dehumidify the great outdoors. Make sure that the space is sealed up tight before you flip the switch

 

[Nomorenoise]

Without an air barrier between the foam and attic, you're only insulating the roof, not creating a conditioned attic. Your dehumidifier will be working overtime to handle moisture from the entire house. To properly condition the attic, seal the foam layer continuously. Otherwise, humid air will seep in from the house. Think about adding a vapor barrier or more air sealing where the foam meets the attic or just condition the whole attic well.