Unique Roof Sheathing- 3" Thick Material

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woodburn

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Oct 26, 2007
221
Long Island, New York
I am thinking about insulating and sheetrocking my upstairs ceilings. Right now I have exposed beams and can see the actual roof sheathing. It is obviously an outdated material (my house was built in the sixties). It is about 3 inches thick and it seems to be a type of very compressed paper (it's pretty hard though). I cut in two skylights a few years back, so I know for sure there is nothing else like plywood or any other insulation. Just the sheathing itself with asphalt shingles on top. Needless to say my upstairs gets cold and doesn't hold the heat like the downstairs.

Is anybody familiar with this material? I want to insulate and rock, but I am told by a neighbor that this roof needs to be exposed on the inside to get the airflow underneath. I don't want to close everything up if the roof will rot. I am hoping to not have to deal with baffles on the inside and vented sophit on the outside (my house has 3 foot sophits with unvented sophit siding recently done). Also, I would have to cut for the ridge-vent to get the benefit from going that route. Does anybody know if I can just close this up and forget about it?

Thanks
 
woodburn said:
I am thinking about insulating and sheetrocking my upstairs ceilings. Right now I have exposed beams and can see the actual roof sheathing. It is obviously an outdated material (my house was built in the sixties). It is about 3 inches thick and it seems to be a type of very compressed paper (it's pretty hard though). I cut in two skylights a few years back, so I know for sure there is nothing else like plywood or any other insulation. Just the sheathing itself with asphalt shingles on top. Needless to say my upstairs gets cold and doesn't hold the heat like the downstairs.

Is anybody familiar with this material? I want to insulate and rock, but I am told by a neighbor that this roof needs to be exposed on the inside to get the airflow underneath. I don't want to close everything up if the roof will rot. I am hoping to not have to deal with baffles on the inside and vented sophit on the outside (my house has 3 foot sophits with unvented sophit siding recently done). Also, I would have to cut for the ridge-vent to get the benefit from going that route. Does anybody know if I can just close this up and forget about it?

Thanks
Click to expand...

Sounds like it might be fiberboard, not sure without seeing it. Got any pics?
You need ventilation between the rafter, or the roof will rot out from the inside out.
What you can do, is first off tear the old shingles off. If the old decking is solid, go over top of it with a 3" or 4" polyicocyanurate (spelling) board they make with plywood or pressboard already attached to one side.
The deckboard side faces out, you screw it into the rafters with commercial grade deck screws that penetrate the rafters say 1-1/2". You can get all this at a local roofing supply company. The you just felt paper the top and shingle as normal.
If you can leave the old decking on no inside work needed, accept maybe paint the underside of the old decking. If decking must come off, depends on how aesthetic you want it inside. The iso board has a paper surface on the bottom side, but if I remember correctly it has small holes in it. Can prolly be painted. We always used it over metal decking on commercial jobs. The R value is between 5 and 8 per inch I think.
Here is a link with some generall info......http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11620
 
Consider doing a "cold roof"- where you leave the existing decking in place, and then go over it with insulation (polyiso board as Hogwilds suggested), then an air gap (attained & maintained by strapping as spacers) so that the whole thing can "breathe" (with screen around the edge to keep creatures out) and then new sheathing and then new roofing.

If your existing sheathing has not rotted yet, then I think that with the ventilation that the cold roof will offer would let you leave the existing sheathing and inside finish in place.

Google "cold roof" and here are some depictions
www.cedarbureau.org/installation/roof.../Roof-manual-p17.pdf
 
I have a 60s era house with that same stuff except more like 6" thick. Some rocket scientist designed a roof system with a 22' span of flat roof supported by 4x6s on 2' centers in the snowbelt. After the beams sagged, someone else came along and put 14" steel on top of every 4x6 and then bolted them up to the steel. There is a 10" airgap between the old roof over the paperboard and the bottom of the I-beams. Last year, I put trusses with big overhangs over the whole thing. I have wondered what to do with the paperboard as well. Insulate above it or cut the goofy beams and paper board out and have 10' ceilings. Any idea what the insulating value is?
 
Using foam insulation requires an air space and good venting to cool it. Rigid fiberglass won't melt down like foam can.
 
LLigetfa said:
Using foam insulation requires an air space and good venting to cool it. Rigid fiberglass won't melt down like foam can.
Click to expand...

Not the polyiso foam-- it is very frequently used right under commercial membrane roofs with no spacing or ventilation at all. I think venting is a good idea, but for other reasons not having to do with the needs of quality foam board.
 
I went searching for info and found out that heat buildup will shorten the life of shingles and for that reason, JM makes a vented nailboard panel bonded to polyiso foam. http://www.specjm.com/files/pdf/Vented_Nailboard_RS-5164.pdf

I take back my suggestion for rigid fiberglass with no venting.
 
Thanks for the ideas. Unfortunately, a few years ago when I cut those skylights in, the whole roof was ripped and re-shingled. That would have been the time to use the vented polyiso everyone is talking about. I wouldn't think of doing that now. I wouldn't mind insulating from the inside then rocking because it would let me run wiring and such. Also, solarandwood- my beams are also 4x6, but they are 4' on center. I was hoping to be able to by the 4x8' sheets of foam insulation and insulate from the inside. Then put 2x4's between the beams so I can sheetrock. What if I don't put the foam right up to the ceiling and leave about 1" airspace? Would this do anything without vented sophit?

Here are some pics
 

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What if you glued the foam tight to the existing ceiling and then glued and screwed strapping through it into the ceiling. You could then screw the drywall into the strapping and the air space would be on the warm side, not the cold side where moisture could condense.
 
LLigetfa said:
What if you glued the foam tight to the existing ceiling and then glued and screwed strapping through it into the ceiling. You could then screw the drywall into the strapping and the air space would be on the warm side, not the cold side where moisture could condense.
Click to expand...

Thanks LLigetfa, but I'm not sure what you mean by that. The way I'm reading that, I'm thinking that once I glue the foam right to the ceiling, there will be no airspace/ventilation. Putting strapping between the sheetrock and foam would allow airspace there, but I'm concerned about the roof rotting, not the foam. Plus once that sheetrock is up, how is air circulating up there.

Right now you can see from the pic that the air on the inside of my house is what circulates and touches the ceiling, which is the actual roof. Once I put sheetrock, regardless of whatever I do with insulating, the air from my house will no longer be passing over the ceiling and giving it ventilation.
 
You could get the isoboard 4' x 8' sheets. and if possible screw it up to the underside of the existing deck with the deck board facing down, then install your drywall right to it?
Just a thought. Not sure if you have anything to screw it to though?
 
woodburn said:
Thanks for the ideas. Unfortunately, a few years ago when I cut those skylights in, the whole roof was ripped and re-shingled. That would have been the time to use the vented polyiso everyone is talking about. I wouldn't think of doing that now. I wouldn't mind insulating from the inside then rocking because it would let me run wiring and such. Also, solarandwood- my beams are also 4x6, but they are 4' on center. I was hoping to be able to by the 4x8' sheets of foam insulation and insulate from the inside. Then put 2x4's between the beams so I can sheetrock. What if I don't put the foam right up to the ceiling and leave about 1" airspace? Would this do anything without vented sophit?

Here are some pics
Click to expand...

Yep, I have the same ones just thicker. It was hard to tell from your picture, are your 4x6s rafters? How tall are your ceilings? If you have room, I think I would fur them out with 2x8s, put fiberglass batts in and sheetrock over it. Just box out the skylights. Then cut in full length soffit and ridge vents. The paper may still rot but I doubt it would happen before it needs to be reshingled anyway.
 
If there is no airspace on the cold side of the insulation, there is no need for venting. They would be like SIPs where the dew point would be within the foam insulation. Just make sure there is vapour barrier directly behind the drywall.

SIPs (Structured Insulated Panels) don't have venting except as noted for cooling to prevent shingles deteriorating.
 
SolarAndWood said:
woodburn said:
Thanks for the ideas. Unfortunately, a few years ago when I cut those skylights in, the whole roof was ripped and re-shingled. That would have been the time to use the vented polyiso everyone is talking about. I wouldn't think of doing that now. I wouldn't mind insulating from the inside then rocking because it would let me run wiring and such. Also, solarandwood- my beams are also 4x6, but they are 4' on center. I was hoping to be able to by the 4x8' sheets of foam insulation and insulate from the inside. Then put 2x4's between the beams so I can sheetrock. What if I don't put the foam right up to the ceiling and leave about 1" airspace? Would this do anything without vented sophit?

Here are some pics
Click to expand...

Yep, I have the same ones just thicker. It was hard to tell from your picture, are your 4x6s rafters? How tall are your ceilings? If you have room, I think I would fur them out with 2x8s, put fiberglass batts in and sheetrock over it. Just box out the skylights. Then cut in full length soffit and ridge vents. The paper may still rot but I doubt it would happen before it needs to be reshingled anyway.
Click to expand...

Yep, they're 4x6.

So it seems I either need to cut the ridgevent in and put the vented sophit, or do it from the outside, which is not an option. Does everyone concur that if I just insulate and rock WITHOUT cutting in the ridgevent that it will cause a problem?
 
If you are going to insulate on the inside, and if you include a good vapor barrier behind the sheetrock (I recommend a product called TuTuf, which doesn't rip as easily as clear poly, and lasts much longer (It's been weird to open up walls or attics and find clear poly that all got brittle and went to shards), with sealing of the barrier around all outlets, etc., then I don't expect that you'll have problems.
 
Moisture (condensation) and the need for subsequent venting is brought about by moist air leaking into spaces on the cold side of the insulation. Rigid foam installed without air spaces and with a proper vapour barrier installation negates any need for venting. There are many cathedral ceiling spray-in-place insulation jobs that have no venting and no need for venting.
 
LLigetfa said:
Moisture (condensation) and the need for subsequent venting is brought about by moist air leaking into spaces on the cold side of the insulation. Rigid foam installed without air spaces and with a proper vapour barrier installation negates any need for venting. There are many cathedral ceiling spray-in-place insulation jobs that have no venting and no need for venting.
Click to expand...

This sounds promising. If the moisture leaks from the cold side of the insulation, then do I still need to put a vapor barrier under the sheetrock? The inside of my house is the warm side, so is the vapor barrier just an extra measure?
 
The building code is quite complacent when it comes to vapour barrier. I am a firm believer of a well sealed envelope both inside with vapour barrier and outside with Tyvek house wrap. I seal all edges with acoustical sealant and Tuck tape. Where it has to transition from warm to cold, like at window openings, I bring the Tyvek house wrap in to seal to the vapour barrier.
 
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