Help insulating an unconditioned 4 season room.

[NBraun]

This is mostly regarding the roof, but figured id included the whole room for clarification. I am rebuilding our enclosed porch into a unconditioned 4 season(hopefully) room. The roof and walls will be new, but am keeping the existing roof. Im trying to insulate it as much as i can(within reason) to help keep it comfortable year round. I also refuse to use spray foam.

Currently it is a hipped porch roof with 2x4 framing. I would like to vault the ceiling and use T&G boards for the interior finish. This is where im not 100% sure what to do. I plan to treat it as a non vented roof. I will fir out the 2x4 rafters with another 2x4 to get 7" of space. Then use R-23 rockwool with a 1" air gap along the roof sheathing. After that use furring strips perpendicular to the rafters and attach 2" polyiso or rockwool board. The only issue with this, is i'm not sure how best to attach my T&G after all this.

Does this sound correct? Am I thinking too much into this? I'm open to any and all ideas.


Walls will be either 2x4 or 2x6 framed with tar paper vapor barrier on the outside with rock wool batts.

Floor is 2x10's with tar paper barrier under the OSB with rockwool batts as well, then 2" rockwool board nailed to the joists from underneath.

 

[pembol]

This is mostly regarding the roof, but figured id included the whole room for clarification. I am rebuilding our enclosed porch into a unconditioned 4 season(hopefully) room. The roof and walls will be new, but am keeping the existing roof. Im trying to insulate it as much as i can(within reason) to help keep it comfortable year round. I also refuse to use spray foam.

Currently it is a hipped porch roof with 2x4 framing. I would like to vault the ceiling and use T&G boards for the interior finish. This is where im not 100% sure what to do. I plan to treat it as a non vented roof. I will fir out the 2x4 rafters with another 2x4 to get 7" of space. Then use R-23 rockwool with a 1" air gap along the roof sheathing. After that use furring strips perpendicular to the rafters and attach 2" polyiso or rockwool board. The only issue with this, is i'm not sure how best to attach my T&G after all this.

Does this sound correct? Am I thinking too much into this? I'm open to any and all ideas.


Walls will be either 2x4 or 2x6 framed with tar paper vapor barrier on the outside with rock wool batts.

Floor is 2x10's with tar paper barrier under the OSB with rockwool batts as well, then 2" rockwool board nailed to the joists from underneath.

For an unvented roof assembly you want the impermeable insulation (the polyiso) closest to the roof deck and carefully sealed. The rockwool goes below that. If you are replacing the roof covering, have you considered putting a couple of layers of foam on the outside?

Unvented Attic Insulation | Building America Solution Center

Guide describing methods for insulating an unvented attic along the roof line.

basc.pnnl.gov

 

[billconner]

What climate? It all starts there.

 

[NBraun]

For an unvented roof assembly you want the impermeable insulation (the polyiso) closest to the roof deck and carefully sealed. The rockwool goes below that. If you are replacing the roof covering, have you considered putting a couple of layers of foam on the outside?

Unvented Attic Insulation | Building America Solution Center

Guide describing methods for insulating an unvented attic along the roof line.

basc.pnnl.gov

I spent a few hours today looking into this, not sure how I managed to miss that!

Can the Poly ISO be touching the roof deck? I've seen where you cut the Polyiso to put in between the rafters and you seal with canned foam. I would be fine doing that.

I'm trying to avoid tearing off the roof. It's new as of 2 years ago, so I would prefer to not have to tear it off, but the porch is small enough, that if I HAVE to it wouldn't be the end of the world.

What climate? It all starts there.

Zone 4, upper midwest.

 

[pembol]

I spent a few hours today looking into this, not sure how I managed to miss that!

Can the Poly ISO be touching the roof deck? I've seen where you cut the Polyiso to put in between the rafters and you seal with canned foam. I would be fine doing that.



Zone 4, upper midwest.

Yes, the polyiso or XPS can be against the roof deck and sealed with can foam.