I've been looking around and Permatherm uses EPS while other (OSB SIPs) say EPS is no good and only Polyurethane is good? Why does one chouse EPS while other use Poly? I like the beneifits of Metal sips but love the insulation of wood sips.. Where do I find a balance?

The vast majority of SIPs are EPS foam. That being said I've seen a higher percentage of metal SIPs being done with Polyiso. Metal versus wood sips, EPS versus ISO. You will find far more opinions than manufacturers.

Posted By Brian on 13 Feb 2013 09:57 PM
I've been looking around and Permatherm uses EPS while other (OSB SIPs) say EPS is no good and only Polyurethane is good? Why does one chouse EPS while other use Poly? I like the beneifits of Metal sips but love the insulation of wood sips.. Where do I find a balance?

Brian,Permatherm stopped making PU due to blistering/delamination caused by offgassing,
the liability was not worth it
the truth is most OSB SIPs are EPS as well
as Torben said , you will find many opinions......
our own experience with PU is, the thickness is inconsistent, need to use a mask when cutting, the dust is an irritant to skin and eyes
our installation crew much prefers EPS

That was the little piece of info I was looking for.

PU foam is naturally almost fire proof. When exposed to flame it will form a char layer and then stop buring. The maximum working temperature of an EPS core panel is 160 degrees Fahrenheit. EPS foam will melt at 180 degrees Fahrenheit and burn at 212 degrees Fahrenheit. The maximum working temperature of a PU core panel is 300 degrees Fahrenheit. PU foam will degrade at 460 degrees Fahrenheit and burn at 2200 degrees Fahrenheit.

Posted By JeffD on 14 Feb 2013 08:09 PM
PU foam is naturally almost fire proof. When exposed to flame it will form a char layer and then stop buring. The maximum working temperature of an EPS core panel is 160 degrees Fahrenheit. EPS foam will melt at 180 degrees Fahrenheit and burn at 212 degrees Fahrenheit. The maximum working temperature of a PU core panel is 300 degrees Fahrenheit. PU foam will degrade at 460 degrees Fahrenheit and burn at 2200 degrees Fahrenheit.

I am curious if there is a documented case of a steel SIP building or roof with an EPS core that melted or burned due to an external (forest fire) or internal fire?

I'm not saying it can't happen, I am just curious to see if a documented case has happened. 

A steel SIP with an EPS or PU core has no "air" within the core. The key factor is making sure to protect the SIP with 5/8" or fire rated drywall on the interior and a fire resistant external coating, either stucco for the wall and metal or asphalt shingle roof.

I'm not a fire expert but if there is no external fuel source near the SIP, then I can't see it melting or burning. In the case of an internal home fire, with numerous fuel sources (furniture, etc), the drywall provides some protection but in a house fire the internal temps can easily see over 500F and both the PU core SIP panel and EPS core SIP panel will melt/burn and fail when subjected to those kinds of temps.

Aged PU generally has much higher R value than EPS. Because of the way PU panels are made, they sometimes have less thermal bridging than EPS.

Wire chases can be more problematic with PU as conduits need to be in place as they are making the panels. As long as one plans out the exterior electrical for the panel maker, Ive found it not to be a big deal compared to EPS.

Ive not experienced or seen the problems with PU that competitors bring up with PUs inconsistencies.

With wood SIPs, EPS is easier to make field changes. EPS foam can be easily recessed with the wire guns. PU requires a bit more labor to "claw out" the foam for the 2x.

As for worker inhalation concerns, EPS is a little worse in my opinion due to the smoke and fumes from melting the foam.

But most closed cell polyurethane is blown with HFC245fa (or other HFCs of similar impact), and in most houses the net lifecycle greenhouse gas footprint of the HFC blowing agents exceeds the total lifecycle energy use it offsets past the first R8-R12 or so.

EPS is blown with pentane that has only about 0.05x the greenhouse potential of HFC245fa, and will be greenhouse-gas neutral against energy use offsets even at R50 in under 10 years, in most places.

There are lower-impact blowing agents coming on the market (eg Honeywell Solstice, released only last November), and a very few closed cell PU products out there are water-blown, but until/unless a PU SIP manufacturer is going to document that they're only using low-impact blowing agents (< 10x CO2) on the foam, I'm neither recommending nor using them, despite the ruggedness and performance advantages of polyurethane foam.

Posted By Dana1 on 21 Feb 2013 02:28 PM
But most closed cell polyurethane is blown with HFC245fa (or other HFCs of similar impact), and in most houses the net lifecycle greenhouse gas footprint of the HFC blowing agents exceeds the total lifecycle energy use it offsets past the first R8-R12 or so.

EPS is blown with pentane that has only about 0.05x the greenhouse potential of HFC245fa, and will be greenhouse-gas neutral against energy use offsets even at R50 in under 10 years, in most places.

There are lower-impact blowing agents coming on the market (eg Honeywell Solstice, released only last November), and a very few closed cell PU products out there are water-blown, but until/unless a PU SIP manufacturer is going to document that they're only using low-impact blowing agents (< 10x CO2) on the foam, I'm neither recommending nor using them, despite the ruggedness and performance advantages of polyurethane foam.

Wish the GBT had a button

The blowing agent concerns are an excellent point. I feel that the global warming impacts of different foams could be a drop in the bucket compared to the millions of other environmental and societal costs of our dirty energy use.

Luckily, they are beginning to change out for more ozone friendly alternatives. Should we not use PU until they have made the switch? Perhaps. Manufacturers should take note that people are avoiding PU from the blowing agent concerns.

For those of us that are trying to squeeze out the most R value per inch, PU is still one of the best choices available. I also think its possible for PU products to better control air infiltration which can have a much bigger impact on the energy use picture than R value.

Closed cell polyurethane is an extremely useful material for air sealing and moisture control in building assembly stackups. Don't throw the baby out with the bathwater. A flash-inch on band joist or cathedral ceiling roof deck adds a LOT of moisture resilience to the assembly.

But despite it's excellent thermal performance, using it as primary insulation in any assembly is a net environmental negative, even at code-min R values (and DEFINITELY for high-R assemblies.)

FWIW: Contrary to industry lore, open cell foam does a better job of air sealing studwalls & rafter bays than closed cell, probably due to it's much higher expansion multipliers during installation. (You can have less than perfect aim and it'll still push it's way into the gaps.) The folks at Building Science Corporation have been carefully measuring the air leakage and it's effects on thermal transfer with many different insulation types in laboratory controlled & built stud walls. While closed cell foam makes tighter walls than damp-sprayed cellulose (and WAY tighter than any batt solution), it's not perfect, and it's as tight as open cell polyurethane walls.

Seeking out the lower impact variants is worthwhile- ASK the vendor what blowing agent is used, and also what the CO2 greenhouse gas multiplier is (or look it up online.) Many blowing agents go by proprietary names (like Honeywell Solstice, which is the good stuff), and not all of the greenhouse impact data is easy to find.

Water blown goods are inherently lower impact (H20 has a lower greenhouse potential than CO2), so products like Aloha Energy's lineup or Icynene MD-R-200 are about as green as it gets in the 2lb foam biz. I suspect MD-R-200 is more widely available in N. America than the alternatives, but not all Icynene installers are using it. But if they get 3 inquiries a month about it they might. Aloha Energy is a much smaller manufacturer, with far fewer installers- I have only 2 contractors handling their goods within an hours' drive of my location, whereas there are easily a dozen Icynene contractors in the same radius (though most do not have MD-R-200 in their standard lineup, some do.)

Almost all open cell spray polyurethane is water blown, and is in no way comparable to the closed cell goods.

Rigid XPS has the same issue, most of which is blown with HFC134a. In Europe HFC blown XPS has been banned, and is blown mostly with CO2 (which strangely, has only 1x CO2 greenhouse impact. :-) ), but the resulting product has the same R/inch as EPS of similar density (R4.2/inch for the standard 1.5lb goods.) But it's vapor permeance is about as low as the HFC-blown goods, and much lower than EPS (~1.2-1.5 US perms @ 1 inch for the 1.5lbs goods), and is thus comparable from a moisture control point of view.