Question for the

I have installed fiberboard, ISO, and tapered styro-foam (can't recall its proper name) in concert with IB membrane(pvc). Out of the three, which insulation will work best for TPO and/or what specific types of roof structures do you reccomend for the insulation installation?>>>

That all makes sense. What they all seem to hate is field-assembled systems. Filled grids used to be the norm. If they are not done meticulously though, they rot. I did one on my own home fifteen years ago and it is functioning perfectly. Back then if you said 'vent chute' they'd look at you like you were dingy. They said complete fill obviated any need for air space. Basically they were wrong. Anyway, just to be doubly sure, I installed ridge vent (without any vent chutes of course) and choked it down a bit. Vapor drive will send any moisture out, I guarantee it. There is not a drop in there. I took it apart recently to check for mice and ants. Lack of moisture confirmed.>>>

4 inches poly iso @ 6.0/ inch. is being liberal...+ all the other stuff you mentioned. drywall, osb, shingles, roll roofing, felt, air space, etc...

http://www.arcat.com/specwizard/07222hun/

as far as GAF and icynene.....none of the manufacturers approve open cell poly foam., but with closed cell, they have no problems, that is as far as I know from an inquiry to my rep last July. I discussed it with roofdude and it seems that they approved it then, but I agree that a vented panel makes most sense when putting composite shingles down on sheathing.>>>

builderr, are you taking your vented panel info from a Hunter site? Just wondering. R-25 to R-28 includes how much poly iso? You left that part out. What I get from way more investigation than I want to be spending is: inside air film @.61, outside air film@ .17, 1/2 inch sheathing @.63, comp roofing @.44, Air space@<1.0 plus insulation per type per inch (so long as one type is not compressing another type) and dependent upon initial value or aged ratings.

I did read that a dead air space is accounted R-5, but dead means dead, which is virtually impossible to obtain. A vent chute is most certainly the opposite of dead air space. They count 1-4 inches of air space as variable around 1.0

You ought to see architects, manufacturers, engineers, and inspectors scramble when they contemplate nailbase and drag up their stories of improperly installed filled grids that trapped moisture. If you check the memos from GAF, they won't even allow comp over sheathing that has rafter bays filled with sprayed in place icynene, although that is not because of moisture. People are getting very twitchy about all this stuff these days.>>>

phenolic foam has an r factor of 8 per inch... it has a shrink factor that makes it a problem in some applications. poly foam has a good r factor....most poly=iso board have r factor of 6.2-6.6. the problem with it is reduced r factor due to aging.

the vented poly iso panels with an air space and a layer of 1/2 OSB claim an r factor of r 25-28, using air space and osb in their calculations. I am bidding work now to install these panels, which can be made up to 4 ft x 12 ft to go over existing framing/ sheathing on structures with 2x6 rafter cavities allowing only r 19...increasing these same buildings to r 40. adding 1 3/8 poly-iso to interior and then sheetrock adds r 10.>>>

P.S. You can get any length fasteners you need.>>>

I wish it were 7 per inch. You would have to show me a link before I agreed with that, even though agreeing with you is my preference. Long term thermal resistance (LTTR) values knock the heck out of things. My tables show I need to install 3 inch iso with a half inch skin just to get to R-19. For roof assemblies we get to add up other components though, including top and bottom air films, the roofing material, the existing sheathing, etc. to derive our total R-value. I'm working out one now where I'm actually up against weight considerations. This state has just gotten so difficult to do business in it is unbelievable. Even the inspectors are weary of it and they love this kind of sh.t.>>>

Isocyanurate is around R-7 per inch, give or take, so you get R-Value, but you would need over 5" to get near the R-38.

Ed>>>

quote...That iso with the wood skin usually goes by the term 'nailbase.' Don't know what you're shooting for, but you aren't even going to get R-19 with 2 inch poly-iso, let alone R-30 or R-38. That nominal 2 1/2 inch stock with four inch screws is going to poke through a bit in places, no?

That is insteresting info concerning the R-value, I have been instructed in the past to install this "nailbase" board on several 4/14 pitch res. roofs (then shigle it with arc. shingles) that initially had no insulation in the beginning. So you can be inferring that this may have been a unneccessary upsale?

There is no cavity for the install of insulation! The 4 inch screws are the only option, don't recall if 3 1/2 inch screws are on the market>>>

Not sure I had any legitimate rationale for thinking it, but I was assuming there is no cavity. As you point out, why else would you insulate from above?>>>

If this is a wood structure, wouldn't the costs of insulation best be served by installing fibreglas in the ceiling joists/ rafters? >>>

That iso with the wood skin usually goes by the term 'nailbase.' Don't know what you're shooting for, but you aren't even going to get R-19 with 2 inch poly-iso, let alone R-30 or R-38. That nominal 2 1/2 inch stock with four inch screws is going to poke through a bit in places, no?>>>

Thinking of going with the 4 x 8 fiberboard but have never installed on a 2/12 residential, but I have installed the f-board on a flat apt bldg with. I am not quite sure it though. Now, I have installed 2 inch ISO-POLY insulation with a 1/2 inch cdx board glued to it, it will require 4 inch screws to fastened. I am leaning toward the ISO-POLY glued board. Will this work better?>>>

:laugh: :laugh: :laugh:

Mike, you kill me.

I really am glad I never put down a TPO based on what you have had to say about it in the past.

For your roof situation though, you are going to want to maximize the R-Value, unless that is not an important consideration for your area, but if it is, then a double layer of Isocyanurate with staggered seams would fit your bil the best.

What are the pricing considerations that you desire to meet?

Ed>>>

It doesn't really matter too much what you use. All of those insulations will last longer than TPO.>>>

If part of the scope of your project involves the tapered products, that is the first part...then i would go with whatever your manufacturer requires to warranty your install. Either way....you need a compatible rigid to adhere, or torch to, but deftinitely not directly to the EPS. Hunter has always been my choice.....their vented panel makes a lot of sense for a lot of reasons that I'm sure you understand.>>>