Exposed polyiso on roof
I have a potential problem I could really use some help with. We are performing an energy retrofit for an old house near Rochester, New York. We stripped the roof and replaced most of the sheathing with taped Zip sheathing. We then laid down 3″ of reclaimed polyiso insulation. Our plan was to lay down a second layer of polyiso, then an underlayment, purlins, and metal roofing.
We worked through October and finished with the Zip sheathing and the first layer of polyiso. Our hope was to finish the prep by mid-November and have the roofer install the metal roof. Unfortunately, winter arrived early with a vengeance with an early November snow storm. Between poor weather, holidays, and schedule conflicts, we have made little progress on the roof since early November. Now my roofer is saying this winter is too harsh and we will likely need to wait until spring.
So, what do I do with the exposed polyiso on the roof? Can I leave it through the winter? Do I continue to wait for some days here and there to continue the work, or should I try to throw a tarp over roof?
I considered installing Solitex Mento, which can be used as a temporary roof and I’ll get the benefit of a more robust air barrier. But the gentleman from FourSevenFive said I would need to install the second layer of polyiso before the Mento, otherwise the fasterners for the second layer of polyiso will compromise the integrity of the Mento.
What would you do?
FYI, the house is unoccupied and gutted. I noticed small leaks in a couple of places. But, with this house being completely open, I’m not worried about that. I just don’t want to lose the $2,000 of polyiso currently on the roof and the hours of labor.
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Replies
I would be most concerned with water getting into the polyiso while it’s exposed. What I would do is to get some black (better UV resistance) polyethylene sheet, cover the roof with it, and run some small (~1/8” or so) diameter Dacron rope from eave to eave over the peak every 3-5 feet or so to hold it down tight. Be especially careful of the edges of the poly where wind will try to get underneath and lift it.
The poly sheet will act as a temporary roof, will be slick so snow and ice can slide off (somewhat, but better than something with a rough surface), and will protect the polyiso from both rain and sunlight, and any snowmelt too.
Bill
Good suggestion. However, how can I tell if the polyiso is already ruined? It's been exposed to the elements (rain, snow, ice) for two months now.
Frankly, it was purchased as reclaimed insulation. Who knows its history. I would guess that it's been exposed to the elements many times. I know reclaimed polyiso has become very popular, but I'm reading technical bulletins about the importance of keeping polyiso stored dry or else the insulation value will degrade. Well, that would mean that no one in their right mind should ever invest in reclaimed material.
My question is: if I cover my polyiso with a waterproof, but permeable membrance, such as Solitex Mento, will it eventually dry out and be just fine? Or is it ruined due to being exposed to the elements for too long? Visually, it looks OK, but if its R-value has significantly degraded, it's pretty worthless.
If I have to rip it all off and throw it into the dumpster, that would be a big loss.
Others here may have better information, but I believe that the R value degrades when the polyiso is actually wet, because the water in the insulation conducts heat. Once it dries out, the R value returns.
If the polyiso is pretty well fastened, then Mento or another self-adhesive underlayment would probably work well as a temporary roof and as your air barrier if detailed properly. I wouldn't worry about the later fasteners too much, as you will be installing another roof at that point.
Will you be stuffing the rafters with fluffy insulation, and when?
Dense pack cellulose in the rafter bays.
That would be very reassuring if I can just cover the polyiso with a breathable but waterproof membrane, and know that the insulation will eventually dry out and be OK.
I would leave it. I have left reclaimed felt faced polyiso sit outside for a couple years and other than the edges getting more yellow it was still dry when I cut into it.
I think some of the concern with polyiso getting wet is overblown because in flat roofing they don't want the felt facer getting wet for even one rain storm, which has nothing to do with the polyiso itself.
If you are really paranoid about it, I would do 3 layers of insulation instead of two. Absolutely not worth paying someone to remove insulation.
If you are determined to drape something over the roof I would not use plastic. House wrap or something breathable would be better.
My neighbor stretched a silver tarp tight over his old roof a couple years ago. It's hidden in the woods and looks like it is supposed to be like that..........I keep thinking, why do we waste all this money on roofing.........seriously tho, it will work till spring comes.