Exterior Rigid Foam Insulation With Metal Siding
Hello all,
Owner-builder located in climate zone 5A, currently in the process of getting foundation walls poured and just found out our exterior insulation order (Rockwool Comfortboard 80 R6 1.5”) will not be filled, we are now frantically trying to come up with the best plan B that we can.
Little background on our wall assembly, 2×6 framing, 16” OC, with Rockwool R23 Comfortbatt between the studs, Zip sheathing (taped and rolled), covered by our exterior insulation?!, rainscreen strapping and corrugated metal vertical siding.
I am currently trying to figure out what our best insulation option is with the aforementioned Rockwool interior insulation and metal siding on the exterior. Have researched and read multiple GBA and JLC articles on using foam and fluffy insulation together. My understanding with our wall assembly we would need at least R7.5/2”/27% of foam to be safe with our R23 fluffy interior insulation.We have been trying to build as “green” /environmentally friendly as possible and therefore had been working to use the least amount of foam possible, but not sure if we can do that now.I am wondering if my line of thinking here is correct and if using foam behind metal siding is a good idea (condensation issues maybe??).
Also have not been able to locate ANY Rockwool Comfortboard, but have located some Rockwool Rockboard 60 and Rockboard 80.Looking at the technical data sheets, it appears to me that Rockboard 80 and Comfortboard 80 are very very similar, wondering if others have used Rockboard 80 in place of Comfortboard 80 for exterior wall insulation?
Just heard back from Rockwool rep, and sounds like they are able to be used for the same applications, at least in the exterior wall insulation use.
Would love to hear thoughts, and ideas from others.
Thank you Dan
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Replies
Will be watching as I'm looking at a similar build (also very interested in any metal siding details).
Are you opposed to reclaimed polyiso?
Dan,
I wouldn't hesitate to make the switch between any two 8 lb/cu.ft density rockwool product. They're effectively the same, as you've noted.
Kyle B,
That is also my first reaction, have you worked with Rockboard before?
Dan,
I haven't used the rockboard directly, but it's my understanding that most of the differences come from the surface coating on the insulation. Some have a foil or fiberglass face, others, like the comfortboard are unfaced. You can probably ask for a sample to see what it looks like in real life.
Kyle B,
Thank you, we are looking into sourcing some Rockboard 80 to compare with samples we have of the Comfortboard 80.
Kyle,
I have also located some Rockwool Curtainrock 80, do you think I could use the Curtainrock in place of the Comfortboard/Rockboard 80?
Dan,
I took a look at the data sheets online, and for the life of me I can't figure out what the difference is between the two. They both pass practically all the same ASTM tests, and have the same density. *I wouldn't hesitate to use them interchangeably based n what is be read. Perhaps someone else will chime in if there is a legitimate difference.
Kyle B,
I agree, as I looked at the data sheets they seem very similar. For the discounted price that I found this Curtainrock at, it is very intriguing, even with the thickness being twice what we originally planned on using. I too am interested to see if anyone else chimes in. Thank you sir.
Let me know how it turns out!
Kyle R,
No not opposed to reclaimed polyiso, more opposed to new polyiso. But reclaimed would be a better option, not sure if we have that available in my local area or not.
Dan,
I would check Craigslist.
Kyle R,
As you mentioned, I have frequented Craigslist and other similar sites, but with not much luck. It seems that others are probably thinking along the same lines we are and trying to use reclaimed polyiso.
AFAIK, Rockwool 80 isn't greener than polyiso or EPS. And certainly not if you spend the $ savings on something green.
Jon R - I just looked at your link ... very interesting and useful data there. Do you happen to have a source for it? I'd like to look into it further.
Jon R, looking at your attached chart, it seams that rigid mineral wool, while not being completely without drawbacks, seems to be a much better option (if available than any of the foams). Although it is nice to see that EPS and Polyiso are better options than I originally thought.
Greenest in terms of carbon is the lowest number in the rightmost column - rigid mineral wool isn't good. Cost effectiveness is also poor. Better to use cellulose within the wall and 2" EPS on the exterior.
https://www.buildinggreen.com/news-article/avoiding-global-warming-impact-insulation
Around here, reclaimed insulation is often priced higher than a bulk purchase of new EPS. And reclaimed isn't zero carbon just because someone else used it for awhile.
You don't need exterior R7.5 for a safe wall. But it's a good idea if you use low perm Zip and/or don't use an interior side air barrier.
Jon R,
I understand what you are saying regarding numbers in the rightmost column. And also agree that cellulose between studs with foam (or mineral wool or wood fiber) on the outside would be a good(green) option as well.
My understanding of the combination of foam and fluffy insulation is pulling heavily from my reading here on GBA, and articles from both JLC, and BSC respectively.
https://www.greenbuildingadvisor.com/article/combining-exterior-rigid-foam-with-fluffy-insulation
https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing