# Anyone hear the rumor that polyisocyanurate insulation is getting downgraded?



## Grumpy (Oct 29, 2008)

Anyone hear the rumor that polyisocyanurate insulation is getting downgraded from R 6 to ro 5.5 per inch? 

Supposedly a government mandate to reflect the true R value of ISO. Supposedly ISO has a higher R value for the first few years due to various gasses used in the manufacturing process. As these gasses escape over time and are replaced by air, the R value is reduced slightly. This is all rumor, just curious if anyone else has heard it.


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## shazapple (Dec 3, 2010)

Definitely not rumour. You are correct that the R value changes and it is called the LTTR aka "Long Term Thermal Resistance". A lot of the time manufacturers are listing this in their literature (at least up here in canada). I wouldn't consider it a 'downgrade' but more of an improved method of testing the long term R value of insulations. I don't think I've ever used R6/inch for polyiso, more like R5. 

It is not just polyiso, it is any insulation that uses a gas during the manufacturing process (XPS, Spray foam). Here is an interesting article about it, although it is a couple years old
http://www.rci-online.org/interface/2007-03-roe.pdf

Another interesting note is that XPS may be water resistant, but try picking one up after sitting on an inverted roof for 30 years. They tend to be a bit heavier because of all the water and you can bet that kills most of their R value.


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## Grumpy (Oct 29, 2008)

I guess the point I got was that while LTTR is well and good, the literature and brochures still say R6 per inch, and that's what's going to have to change to the 5.5.


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## Pie in the Sky (Dec 21, 2011)

NRCA States 5.6 as the accepted R-Value of Polyisocyanurate and I wouldn’t use any more for calculations. You then get reductions in systems of up to 15% for joints and fasteners. I hope they do have to start stating it, When I used to do alot of QAQC I ran into these shady operations all the time. Recently the insulation didn’t fit correctly in the nailers only to realize the 2" iso was really 1-7/8". That’s a big deal when an R-50 is specified on the job. 

Also this varies with thickness of insulation and Facer! Foil facers keep a higher R-valuse because the foam cannot off gas as much.


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## Pie in the Sky (Dec 21, 2011)

shazapple said:


> Another interesting note is that XPS may be water resistant, but try picking one up after sitting on an inverted roof for 30 years. They tend to be a bit heavier because of all the water and you can bet that kills most of their R value.


You must be mistaken!!! Closed cell foam insulation DOES NOT absorb water... :laughing:

I've had salesman telling me this my whole consulting career. I was a Roofer and have torn off lots of rubbery heavy Blue Board (XPS) Spray foam, and EPS. I think you saying "a bit heavier" was either a gross understatement or sarcasm. It is true closed cell foam will not absorb water under most conditions but in the presence of a thermal gradient it will become saturated.


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