Non-HFC ccSPF, R60 ceiling with skylight
Hi all,
I am currently learning/working on setting my insulation, thermal, air, and vapor barriers given my design and budget. The design is basically a pre-fab 35 foot diameter hard sided yurt. I loved the look of the yurt but have to improve the base package for it to be green. I have developed a wall with a nominal R value of about 46, my basement wall is R20, the basement floor is R18, the floor is R30. I haven’t adjusted for bridging yet. I’ve worked on getting air, thermal, and vapor barriers based on threads/comments, blogs, articles, etc. Pricing out Intus windows. So far so good. I’ve really enjoyed the process.
Here’s the rub of it though, and a potential deal breaker:
The rafters for my metal roof are only 12 inches. The rafters go into a compression ring, the rafter trim is attached to the inside edge of each rafter which then holdd 1×3 cedar. (see attached photo). If I have a 1in baffle (accuvent cathedral ceiling vent), then there is only about 10 in of insulation space remaining. If I did EPS + 2 in thermal dead air gap + EPS + thermal dead air gap + EPS, then the roof is nominally R33 (assuming 1in ply sheathing and 1in cedar are R1, 2 in dead air is R 3.5). I could sub mineral wool with furring/lath and have similar performance–but with greater bridging and still not good enough insulation. If I eliminated all thermal air breaks and just filled with EPS then I can get up to a nomimal R 42. Still don’t hit the R60 I was shooting for that would be consistent with the insulation, barriers and windows I want to put in. There is no point spending the money for well insulated walls, floors, foundations, and passive solar windows if all that hard work is just being lost through the roof. Because there is a dome/skylight, I am already losing heat big time, so it may not be worth it all (I will be using the free version of WUFI once I have it specked out to check if I am just wasting money cause of the skylight/dome). ccSPF at R 6.5/in @ ~10 in, along with plywood and cedar would get me at a nominal R67 (minus thermal bridging and losses to the skylight/dome etc). But I’ve read where closed cell foams have a high GWP because of the HFCs. So I did some digging.
Here’s the question: does anyone know if Honeywell Enovate 245fa or Solstice can just be a drop in substitute for HFC based ccSPF (the website says so)? Can I just get a local contractor to sub this in for the regular HFC based product? These products have a GWP of 1, eqvlnt to water based spray cellulose (I think). I know nothing about this though, and wanted to hear expert insight.
I was picturing adding in the Honeywell products to Icynene MD-C-200, but am very open to other suggestions. Icynene seemed to go well with LEED, didn’t use PBDE’s, and is low VOC.
If I can’t get low/no HFC ccSPF, then I think I may have to abandon the whole design. I just don’t think a roof @ R42 cuts it given the investment in walls, windows, and foundation. I can’t add insulation over the rafter interior because then the ceiling trim would have no where to go. I could in theory double the rafters, but that would mean another compression ring. I am already a bit over budget, so doing a double rafter/compression ring would probably tip the project over into a no – go.
So am I dreaming about subbing in the Honeywell products to make a low/no HFC ccSPF foam?
Is there an alternative to either an R40 roof, or, doing a double rafter set up?
Looking forward to the sage advice, reality check, and ideas.
Many thanks,
-ethan
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Replies
Should say I am a climate zone 6, and to throw it out there for feedback :
R40 ceiling/roof:
cedar > Proclim Intello > 8in EPS > 1 in accuvent cathedral ceiling baffle > 1 in taped? CDX plywood sheathing > ice and water shield over eaves and around dome > 30# felt with plastic cap nails > 24 guage galvanized roof
~ R65 ceiling/roof: cedar > no HFC ccSPF > EPS > 1 in accuvent cathedral ceiling baffle > 1 in taped? CDX plywood sheathing > ice and water shield over eaves and around dome > 30# felt with plastic cap nails > 24 guage galvanized roof
On the substituting blowing agents on the fly, you're dreaming. The local contractor can't just make the swap. Getting the foam at the right density & R value requires tweaks to the temperatures at which the chemicals are delivered, and some tweaks to the chemistry. The chemical manufacturer spends years figuring out how to get it to work with their goop, then specifies all of the installation parameters that will work with their process to get consistently high quality product. If you deviate by very much there will be both quality issues and long term polyol outgassing issues.
Enovate 245fa is just Honeywell's trade name for HFC245fa- the nasty stuff with the huge GWP problem that the industry is slowly pulling away from. Solstice is the low GWP HFO1234ze blowng agent. There are commercial foam vendors using it, but there is also water blown foam.
Icynene MD-R-210 and MD-R-200 are both blown with water, and run about R5/inch, which would get you to R60 nominal at a 12" depth.
In upstate NY a local company Aloha Energy has some 1.8lb water blown R6/inch water blown foams.
http://aloha-energy.com/spray/
Demilec Heatlok HFO High Lift is blown with HFO1234ze (Solstice).
So is Lapolla Foam-Lok 2000 4G
Also, do the math: The annual energy use difference between an R42 & R60 roof is quite small. It's absolutely NOT a waste to have an R42 roof with an R46 wall. You can probably garner bigger reductions in energy use by upgrading the windows than changing the roof from R42 to R60.
If you don't mind the neutral-density look of it, you can probably get an R20-ish skylight with aergel insulation for the dome. Wasco's commercial skylights with aerogel insulation might have something in the right size. https://www.wascoskylights.com/product/lumira-aerogel/ Their website's a bit of a pain to surf- you may have to just call them to see if there's something that will work for you.
Dana, you rock. I thought all the Icynene MD products were closed foam and used HFC in the blowing agents, and the water based products open cell were all ~3.5/in. My bad/learning curve. Either way, the Aloha Energy product is local to my area and bio-based, so I will probably go with that. I've contacted the company for an estimate. I take it the Demilec and Lapolla products are also no HFC? I was mistaken in my read of Icynene, so I wanted to confirm re: the Demilec and Lapolla. I think the Intus windows are the biggest bang for the buck (u of .16ish, shgc of .5-.6 depending) based on my reading here and elsewhere, but if you have a suggestion I am all ears. I really appreciate all the help/insight. I was really bummed earlier today and worried I'd ran up against a deal breaker. THANKS!
Ethan, I am considering building a Bill Coperthwaite tapered wall yurt in Western MA. I wanted it to be as insulated as possible and like you, stumble when it comes to the roof insulation. What did you end up with?