Other types of rigid foam insulation do not use HFC blowing agents, so their global warming potential is much lower. It also provides better soundproofing, and being made with stone, it is fireproof.  Polyisocyanurate foam insulation panels come with a layer of foil on each side to keep the gases in, so there is the potential to solve a bit of a growing problem in wall assembly durability. Foil is a vapour barrier and a very good one at that, it fact it stops even more moisture than the normal 6 mil polyethylene normally used. Anything that begins with "poly" is a plastic, right? Whether the material used was PIR or PE, it was totally inappropriate & caused a small fire to engulf the block. Your price comparison is consistent with the trend. First time i hear about this loss of insulating properties of PIR boards at low temperatures. For example, when both products are used as wall sheathings, the ASHRAE Design R-value for 1” foil faced polyiso is 6.0 per actual inch versus 5.0 for polystyrene, when tested at 75°F mean temperature. As mentioned above, the performance of polyiso drops when it's cold, for that reason we would recommend it being just a component of a wall assembly, one where it could be kept warm, as in having more insulation on the exterior of it.Â. But I persoanally would have no concern whatsover storing furniture in a room insulated with XPS. Now, I've never been one to take the word of an article found on any website, ever, without checking the sources, but as far as I can tell, its called "Reynobond PE" and the PE stands for poly-ethylene. This type of rigid foam won’t absorb water and can act as an semi-impermeable vapor barrier. EPS vs. XPS vs. GPS. the walls and roof i have more flexibilty in what prodiucts i could use. The two options I'm looking at are the Foil faced EPS or the Polyiso. Many van dwellers successfully insulate with XPS and it is one of the most popular options for insulation. You can add as much rock wool as you want, or as little as you have to if there are other considerations like property line setbacks or such, because it won't alter the basic function of the existing wall. I'll stick with those numbers for easy math. Unlike polyiso and XPS, the R-value of EPS is permanent. Depending on building type, construction type, climate zone, orientation, etc., one has to examine the suitability of the limited service temperatures of XPS. Choose rigid insulation wisely, and consider the effect its characteristics will have on the performance of the your project, overall product cost, and the best way to get the bang for your buck. For reference sake, the traditional 6mil polyethylene vapour barrier has a permeability rating of 3.4 ng, making it about 18 times more vapour resistant than building codes allow. On top of that, the ACM cladding was created to emulate columns with large voids, and created a chimney effect. That would mean that it was performing at a level under R2 per inch, and there is no evidence to support that at all.  The NRCA ( National Roofing Contractor’s Association) recommends calculating the R value of polyisocyanurate insulation at R-5.6 per inch when designing for warm climates and R-5.0 per inch when designing for cold climates. The R-value of a product refers to the material’s resistance to heat transfer. This falls in line with the instability of a thermoplastic material. Under the slab, consider EPS over XPS. That way you could do Rockwool and have the vapor barrier like with the foil. And all plastics will burn, though some more readily than others. XPS foam insulation at about 1 inch thick will act as a vapour barrier, EPS foam insulation will start to act as one at about 2 inches, and polyisocyanurate (the one with the foil on both sides) is a vapour barrier at any thickness (foil is waterproof). Rated at R4 per inch; EPS foam insulation boards are more permeable to air and moisture than XPS, but it doesn't retain moisture to the same extent because of it's more closed cell structure and it's breathability which lets it dry out. If PIR r value drops 30% in cold temperatures, doesn't it still match or outperform it's competition in r value? And it isn't a great surprise that an installer hadn't heard that the performance falls off in colder weather since manufacturers present their 'best' results from testing, and in warm conditions it does offer R6-R6.5, so that is laregely the 'accepted' R value of polyiso in the industry.  The room is supposed to be “temporary” so we did not plan on putting drywall up. And then charged the public several million pounds for doing so? As gas escapes, however, the R-value of polyiso can drop over time, but foil and plastic facings can help stabilize that number.  Do you have any suggestions? There seems to be contradictory information about the material used. Excavating around the perimeter may not be possible due to concrete platforms and stairs around 1/3 or more of the perimeter. The information provided regarding r-value loss is incredibly incorrect and misleading. But one fact is indisputable - it burned ferociously. Rigid Foam insulation panels, Polyiso, XPS, EPS, Mineral Wool & Styrofoam © Ecohome, How to Find Qualified Green Building Professionals, natural Green Insulation Products, Like Hemp Insulation panels or Batt Insulation, mineral wool - demonstrated here in roof insulation, article from Building Science Corporation here, retro-fitting insulation when finishing basement, EcoHome Guide to High Performance wall construction here, Video Guide to high performance wall construction and insulation here, graph of the permeability rating of vapor barriers, suitable ‘vapor barrier’ in  residential constrution. Be sure to read the EcoHome Guide to High Performance wall construction here, And watch the Video Guide to high performance wall construction and insulation hereÂ. Our personal overall preference due to its recycled content and versatile applications is probably mineral wool, but as for the petroleum plastic rigid foam insulation products - polyisocyanurate gets top marks for being 'eco' if you are in a warmer climate and can handle its moody disposition. The effect you mention is known as 'thermal drift', and yes it is a real thing, but the drop in  R value per inch of polyiso is not even remotely close to that level. So you can pack more R-value in a smaller space with XPS. Expanded polystyrene insulation and polyisocyanurate foam polyiso are the two main insulation types used in EIFS in North America. Closer examination will show that when comparing R-values, polyiso is less expensive than XPS. Protect insulation from heat and water. Who in their right mind would fail to see the dangers of wrapping a building in flammable poly-anything? I'd use EPS, or even XPS. To test the R-value of rigid-foam insulation, companies use the ASTM C518 Standard Test Method. There may be a case to be made for EPS rigid insulation. You can read all about rigid insulation panels here.  As for how much to install, we have come to realize that for the most part, regional building codes are about half what we ourselves would do. ASTM E84 states, “Testing of materials that melt, drip, or delaminate to such a degree that the continuity of the flame front is destroyed, results in low flame spread indices that do not relate directly to indices obtained by testing materials that remain in place.” In fact, when XPS is subjected to the extreme heat of this test, it melts to the bottom of the tunnel.