More Q&A Spotlight
One of the joys of living in a cold climate is that you may get to experience ice dams—a condition where air and heat escaping the house melts snow on the roof. The melted snow runs down the roof and refreezes at the unheated eave, forming a dam. The cycle continues, only as the melt water repeatedly drains down, the ice dam grows toward the roof peak, and the water soon finds its way under the shingles and into the house.
In a recent Q&A, an architect named Noah, posting as “streamcolab,” writes that he has a 1860s Greek Revival home in Climate Zone 6 that needs a new roof and that suffers from “really bad” ice damming. The second floor of his home sits beneath an insulated 8/12 pitch roof. Like many homes with living space beneath the roof, the sloping ceiling transitions to a flat portion at ceiling height—it’s a straight gable, Noah says, with no dormers.
Unfortunately, the roof and ceiling are insulated with vermiculite that contains asbestos. Although Noah recognizes that vermiculite isn’t ideal, he can’t afford to remediate it right now. “When you have a roof that is actively leaking and limited funds, you have to pick and choose your battles,” he writes.
Noah’s primary concern is to “mitigate the ice dams and moisture within the roof assembly and attic.” The problem is that he doesn’t want to ruin the historic lines of the Greek Revival roof trim details by adding layers of insulation above the roof deck, and he doesn’t want to disturb the interior’s plaster ceilings, which he says are in good condition. Ideally, he needs to make the roof waterproof, then air-seal and insulate his attic and roof deck to prevent continued ice dams.
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4 Comments
Dear Chuck: First, thanks for your detailed article. Ice dams are a perennial problem in Snow Country, like Massachusetts. Two comments:
(1) The Sun: We installed 8" of spray foam under our roof - including the knee wall areas, sealed all air leaks on the roof deck with Grace Ice & Water Shield (100% coverage) and in the attic, created a sealed attic, and ice dams still formed - though less frequently. Why? The Sun heats the roof, snow & ice melt and water runs toward the edge - and freezes. So you can reduce the incidence of ice dams - but the only real solution to stop water leaks is to install a waterproof barrier (e.g. Grace) on as much of your roof as possible. At a minimum 3' from each edge and 3' along 'valleys' in your roof. Grace and similar products are so inexpensive, however, that we covered the entire roof. You should too.
(2) Spray foam is bad: Wrong! Read up on low GWP spray foam, which has been available for years - and is now required:
https://www.sprayfoam.org/hfoupdate/
https://www.greenbuildingadvisor.com/question/low-gwp-spray-foam-vendor-hunt
https://www.greenbuildingadvisor.com/article/is-using-closed-cell-foam-worth-the-trade-offs
In short, low / very low GWP foam products have been available for some time. All of this said, blown cellulose is zero GWP and is the best and cheapest solution for many attics.
BvilleBound
Bville, for some reason, the industry standard for reporting GWP of spray foam only includes the blowing agent, not the resin. They also assume a 75-year service life, which may or may not be accurate. If you include the GWP of the resin, it still has the highest GWP of any common insulation product.
It's true that the new blowing agents have far lower GWP values than previous, HFC blowing agents; at least that's what we have been told. New research shows that the new ones may ultimately be as bad or worse than HFCs. Here's one of many articles available on the subject: https://scitechdaily.com/new-study-uncovers-dangerous-secret-of-green-refrigerants/.
Blown cellulose isn't zero GWP either; a quirk of their reporting is that they don't include what goes into making the raw material, they consider the newsprint to be zero GWP. All cellulose manufacturers use at least some "post-industrial" newsprint, which means it hasn't even been turned into newspapers yet. And the processing required is not zero-energy. It's still my go-to blown insulation but I'm not interested in greenwashing it.
Dear Michael: First, why would you think that the resin in spray foam would 'vaporize' and enter our atmosphere? Second, how do you know 'vaporized resin' would have "the highest GWP"? Third, "post-industrial" cellulose is saved from landfills etc. See: https://shop.gfsmith.com/glossary-of-terms Fourth, NO TYPE OF INSULATION (or energy) is ZERO ENERGY. Neither are humans! We run at ~100 watts per hour, at rest - and up to 440 watts per hour with vigorous activity. So none of these facts are "greenwashing" - a favorite term for Global Warming Deniers, by the way.
I have done a lot of research on the subject, to say the least.
The resin doesn't vaporize; thinking that's what I meant shows a lack of understanding of what GWP means. I recommend researching the topic.
I was a bit lazy with my grammar. I mean that combining spray foam's resin content and its blowing agent, it still has the highest GWP of commonly available insulation products. Traditional XPS is actually worse but the type with low-GWP blowing agent is now very common, at least in my area.
I understand that post-industrial newsprint MAY be landfilled if not used by cellulose insulation manufacturers. That doesn't mean it didn't require resources to produce. I understand why that industry wants to consider it to be carbon neutral, I just disagree that it's a completely fair way to measure its GWP. Currently there are no fully accurate ways to measure the GWP of anything so getting close and being consistent is the best we can do. I just like to understand the nuances of what's behind the numbers.
I am the polar opposite of a global warming denier. I do think that greenwashing is counter-productive.
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