Open Cell v Closed Cell
Several months ago, Martin and Robert Riversong helped me to think through my options on a new home that we have under construction. The discussion centered on the idea that I have made some compromises, for budget and other reasons, which meant that I will be installing code minimum insulation and will not be addressing thermal bridging. With this in mind, I think that my use of foam, either closed cell or open, will be primarily driven by preventing air infiltration. Budgetary concerns plus the Fine Home Building article (June/July 2009) suggesting the both closed and open cell foam exhibit diminishing returns at approximately 3″ and 5″ inches respectively, have led me to price out 3″ of closed cell and 5″ of open. My questions are as follows: (1) does open cell require a vapor barrier? (2) does open cell hold up over time? (3) What other considerations, given these caveats, should I be addressing?
Thanks in advance
Al Charbonneau
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Replies
Whomever wrote that FHB article has clearly drunk the SPF koolaid. The only "diminishing returns" from increased SPF thickness are the financial returns to the supplier and installer, since they can't sell such an overpriced product in thicknesses required to meet or exceed code minimum standards.
If you double the thickness - and hence R-value - of any insulation, you halve the conductive heat loss (ignoring thermal bridging, of course). This is simple physics and all the foam manufacturer's know this. But they've propagated (that's the same root as propaganda) the false idea that there is no thermal advantage to really good insulation levels.
Yes, open cell requires a vapor barrier. We simply don't know the durability or longevity of any spray foam, particularly those which are site applied under infinitely variable conditions with no quality control, but all plastics lose their plasticizers over time and expanded foams lose their low-conductivity foaming gasses over time (some of these agents are toxic to people or to the environment). Other considerations are that petrochemical plastics are non-renewable, environmentally toxic, non-biodegradable, and one of the greatest scourges on the planet.
As I've said umpteen times before: there is nothing green about plastics. Zip, zilch, nada.
Al,
The usual question:
1. Where do you live? The answer to your vapor retarder question depends on your climate. If you are installing the insulation in your walls, however, and if your walls are covered with painted drywall, you should be fine anywhere in the U.S.
2. "Code minimum" means different things to different people. Three inches of closed-cell foam provides about R-19 or R-20; while 5 inches of open-cell foam provides about R-18 or R-19. That isn't much in a cold climate, but if you live in Texas or Florida you'll probably be happy.
As I've written before, it's too bad that the FHB article on spray foam insulation added to the widespread confusion about the "diminishing returns" of thick insulation. Those of us who have been promoting superinsulation techniques since the 1980s have been trying to convince builders and homeowners of the advantages of very well insulated envelopes. Unfortunately, the spray-foam salespeople have been working diligently to convince people of the opposite idea -- the acceptability of thin insulation.
Martin I am glad to see you have upgraded Texas and Florida from "R-10 is probably plenty"
Maybe 40 years from now the idea of Superinsulation in Hot and Mixed Climates may not be so ridiculous.
John,
Actually, all you really need in a hot and humid climate is a loincloth and a hat.
Robert,
I still think "Leroy who prefers the outdoors" may have you "out-greened"
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/15460/pv-peak-demand-and-beopt
;-)
I have always suspected that Leroy might be Martin's alterego
or perhaps Michael Chandler
come on Leroy ......Fess-up
Martin:
Answering your questions
(1) Rhode Island
(2) R 19, R38
I am more than curious about the origin of the diminishing return chart. Was it industry developed? The SPF sales people in our area will sell me as much as I will buy of closed cell or open cell insulation.
I feel like I am speaking with Moses and asking the question "Could you get along with two commandments?" As I said previously, we have had to make a series of decisions which put us where we are. The new house replaces an old house that had a max of R13 fiberglass and no air barrier. At least we are moving up, however slightly. If I had it to do all over again, I would have not planned as much on SPF because it seems that the way to go wrap the house in rigid foam.
At any rate, if I go with open cell foam in the walls and cathedral ceiling both under 1/2" drywall with plaster, you guys recommend a vapor barrier? Closed cell, you do not recommend a vapor barrier?
Enjoy the discussion and website.
Al Charbonneau
Al: Sorry to hear you are not in the Bill Gates Club and have to compromise; that is a theme of life, ain't it? Question: Is there somewhere else you can skimp other than the insulation? My personal opinion, being an insulation freak, is to try to find somewhere else to skimp; maybe not put siding on, or maybe not finish a few rooms, board over some windows and buy them next year, one less bathroom for a year... etc. Once you close up the walls, you're toast. You can always finish a house later; easy for me to say, right? Good luck on the house, either way. john
Al,
If by "vapor barrier" you mean "polyethylene," I would always omit it in Rhode Island. If you end up using open-cell foam, the latex paint you install on top of your drywall will be your vapor retarder.
If you can possibly afford it, maybe you'll consider 5 inches of closed-cell foam.
Yes, you're right that the "diminishing returns" chart — and the notorious R-value bar graph comparing various R-value options to the performance of an uninsulated tent — were developed by the spray-foam industry. To read much more than you ever care to on this issue, visit
https://www.greenbuildingadvisor.com/blogs/dept/musings/it-s-ok-skimp-insulation-icynene-says