Ideas for reinsulating a ceiling

[maineiak]

Hi
I have a camp I am turning into a year round residence. It has a new standing seam metal roof so the work has to start from the inside. The camp has a cathedral ceiling with tongue and groove pine nailed to rafters. It has six inches of fiberglass insulation. The room size is 20ft x 24ft. I f you need more information please let me know. Would it make sense to remove pine ceiling and fiberglass insulation and have it spray foamed ? I have feeling the pine would not go back up too well. The other choice I thought of is cover the existing ceiling with foamboard and strap it and then buy new pine to redo the ceiling. the camp is in Central Maine so it is cold up here. I am looking for feedback and ideas which are greatly appreciated. I've read a lot of posts here and appreciate the knowledge of the people.
Thank you

 

[begreen]

If you're careful and set up a scaffolding you may be able to remove a lot of the paneling intact and in good condition. This will depend in part on how it was nailed up. If top nailed it should be easy.

 

[semipro]

You may want to start here reading about Ashful's project, part of which included insulating a metal roof from the inside.
https://www.hearth.com/talk/threads/insulation-calculations.136769/#post-1835462

 

[maineiak]

Thank you I will read it.
The ceiling is not face nailed it is nailed on the tongue not sure how big the nails are.

 

[maineiak]

If two inches of ridged xps Styrofoam taped well and air sealed under six inches of fiberglass is close to what I would get with four and a half inches of closed cell sprayed foam. The xps would be a lot less mess. Does anyone disagree with this?
Thanks

 

[semipro]

Is there something between the FB batting within the rafters and the metal roof: purlins or decking? I"m trying to get at whether the inter-rafter space is sufficiently air-sealed from the outdoors.

 

[greg13]

Unfortunately the best option is also the most expensive. Your best bet would be spray foam, but the price tag is going to be in the thousands you may never recover the investment. Blown in may be as good and a lot less $$$.
Any way you go, you are going to need to have access to the space.

 

[maineiak]

There is plywood then one coat of asphalt shingles. There is a ridge vent and holes drilled on the eves for venting but no proper vent.
Thanks

 

[maineiak]

Greg 13
There is no access up there now and if I went with xps I would probably go over the existing tongue and groove strap then buy new tongue and groove.

 

[semipro]

There is plywood then one coat of asphalt shingles. There is a ridge vent and holes drilled on the eves for venting but no proper vent

So you have a ventilated roof deck with fiberglass batts below. Is there anything between the airspace under the plywood and the fiberglass? Any kind of air barrier (e.g. kraft paper, poly, Tyvek) on either side of the FG?

I'm trying to get at whether the FG is effectively insulating or not. If air is flowing through it all its doing is filtering the air. Very little thermal insulating is occurring.

Edit: Also, how deep is the between-rafter area?

 

[maineiak]

Between fiberglass and decking there is probably an inch airspace where the fiberglass has settled nothing else. Room side has paper with pine tongue and groove. I'm sure air is getting through. I notice in the summer by afternoon it starts getting warm up there.
Thanks again for the replies.

 

[semipro]

How deep is your rafter space?

 

[maineiak]

I believe six inches

 

[semipro]

As installed, the FG is pretty much useless as thermal insulation. You can't really just add foam below counting the potential l R-value of the FG.
My recommendation:
strip everything back to the roof deck, have closed cell foam sprayed full rafter thickness by a contractor, then install a layer of XPS taped/ sealed, then your ceiling. The XPS layer performs two functions. It addresses the thermal bridging that's occurring across the rafters and creates a secondary air barrier. I suggest that a secondary air barrier is needed because spray foam has demonstrated that it can shrink and pull away from the surfaces its sprayed onto. If you think this is overkill you could forgo addressing thermal bridging and just install another air barrier under the rafters rather than the XPS. Airtight drywall would suffice. If boards are going to be used then you should install a house wrap or some other air barrier against the rafters.
Doing this you've essentially converted to an un-vented roof assembly so your soffit and ridge vents are unneeded and would be plugged with the spray foam anyway.

 

[maineiak]

As installed, the FG is pretty much useless as thermal insulation. You can't really just add foam below counting the potential l R-value of the FG.
My recommendation:
strip everything back to the roof deck, have closed cell foam sprayed full rafter thickness by a contractor, then install a layer of XPS taped/ sealed, then your ceiling. The XPS layer performs two functions. It addresses the thermal bridging that's occurring across the rafters and creates a secondary air barrier. I suggest that a secondary air barrier is needed because spray foam has demonstrated that it can shrink and pull away from the surfaces its sprayed onto. If you think this is overkill you could forgo addressing thermal bridging and just install another air barrier under the rafters rather than the XPS. Airtight drywall would suffice. If boards are going to be used then you should install a house wrap or some other air barrier against the rafters.
Doing this you've essentially converted to an un-vented roof assembly so your soffit and ridge vents are unneeded and would be plugged with the spray foam anyway.

Thanks semipro
I was hoping I could get by with less mess and work and money. Your idea does sound like the best possible solution. I want to do this only once, so I appreciate your advice. I guess I will get some estimates. This will probably delay the work some and will take a lot of prep work as it is full of furniture up there.
Thanks again for your time

 

[semipro]

I was hoping I could get by with less mess and work and money.

I sympathize completely. That said, this is the most critical part of your house's shell to seal and insulate properly. Your resources are well-spent here rather than on walls or floors. If you were do nothing other than air seal it you would probably notice a big difference in comfort and energy use.
Your plan of just adding foam board below the pine may work but you'd have to build up a pretty thick layer to get anywhere near an acceptable R-value given that the FG is not contributing as installed.
Hopefully others here will chime in with some less expensive options.

 

[maineiak]

Is there a reason I can't see my thread on my computer?

 

[Hogwildz]

Make sure there is an airs space between th underside of the roof deck & the fibeglass. I just did the same thing and took the T&G down, reset & tightened up the fiberglass, then installed 2" Polyisocyanurate foil faced foam board (R13). I cap nailed the board to the bottom of the existing truss cords, and then used 1" x 3" lath board screwed through the board into the truss cords. Then reinstalled the T&G to the lath.

You can leave the foam board approx. 1/4" to 1/2" or so way from the perimeter walls and fill in will spray foam in a can. Then foil tape over the field seams , and wallah, nice air sealed barrier. My T&G was installed with twisty nails, not fun at all, but got them down, with minimal breakage. Shot the boards back up with 2-1/2" brad nails, 3 or 4 per latch.

 

[maineiak]

hogwildz
Could you tell me did you notice a big difference in heating with it done this way? This would make it so much easier and cheaper. But I want to do it right.
Thanks

 

[Hogwildz]

Ha

hogwildz
Could you tell me did you notice a big difference in heating with it done this way? This would make it so much easier and cheaper. But I want to do it right.
Thanks

rd to tell as I only got one small room done, and the entire house is cathedral ceiling. Air sealing by far is the best way to retain heat in the house. I'd focus on air sealing more than insulation. But with the better iso boards, you can achieve both. With the crappy stuff your thinking of using, your going to get minimal insulation value from that junk. Go with the Polyiso, it is stiffer, easier to work with, better insulation value and makes a great air seal when done right. I can attest to one thing, there are no flies or ladybugs est getting in through the attic in that room. Where as they did before, and still do in the rest of then house as there is huge gaps everywhere. T&G in not tight at all, and I can only imagine the heat going up and through the T&G and through the F/G and out to the wild blue yonder.

 

[maineiak]

Ha

rd to tell as I only got one small room done, and the entire house is cathedral ceiling. Air sealing by far is the best way to retain heat in the house. I'd focus on air sealing more than insulation. But with the better iso boards, you can achieve both. With the crappy stuff your thinking of using, your going to get minimal insulation value from that junk. Go with the Polyiso, it is stiffer, easier to work with, better insulation value and makes a great air seal when done right. I can attest to one thing, there are no flies or ladybugs est getting in through the attic in that room. Where as they did before, and still do in the rest of then house as there is huge gaps everywhere. T&G in not tight at all, and I can only imagine the heat going up and through the T&G and through the F/G and out to the wild blue yonder.

My choices are the two inch polyiso as you have or take the fiberglass out and have the rafters filled with closed cell foam then reinstall tongue and groove. I'm not sure the extra cost of the spray foam would be worth it.
Thanks for your input

 

[Hogwildz]

You will never see recouped cost of the foam. You could put iso on the bottom of then existing T&G and install new T&G probably for less than the foam.

 

[semipro]

Polyiso is good stuff and is widely used in commercial roofing. I use it in above-ground applications other than roofs, avoiding sub-grade and roof applications only because it can absorb water.

 

[maineiak]

Hogwildz
I'm thinking the way you are. Will I ever recoup the cost of the sprayed foam? It would probably cost me triple what it would cost for the Polyiso.

 

[Hogwildz]

Hogwildz
I'm thinking the way you are. Will I ever recoup the cost of the sprayed foam? It would probably cost me triple what it would cost for the Polyiso.

Doubtful on the return on investment. Foam board and seal well and be done with it.