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Community and Q&A

Mineral Wool Rigid Insulation Price

rodrob15 | Posted in Green Products and Materials on

I’m planning on building a cabin in the next few months and would like to have a 3 inch layer of semi-rigid mineral wool on the exterior. Even though R-values are a little less compared to rigid foam, I think its a superior product given it’s breathable, is insect resistant, mold resistant, and r-values don’t drift over time. I also like that its a green product and doesn’t contain any blowing agents or formaldehyde.

It seems that Roxul Comfortboard 80 is the go to product for exterior applications in the residential market, but it’s very expensive. I’ve talked to local building suppliers that have quoted around $1.25/sqft for the 2 inch version. It looks like big box stores are selling the 1.5 inch version at about $1/sqft. I could probably negotiate those prices down, but it’s still considerably more than foam. I’ve found 2 inch XPS at $0.60/sqft and I can probably improve on that.

Does anyone recommend alternative suppliers or would like to share their experience with mineral wool? Is there a general market cost per square foot I should have in mind for mineral wool? I used to see older posts that praised the affordability of semi-rigid mineral wool compared to XPS, but that seems to have reversed in recent times.

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  1. rodrob15 | | #1

    To add to my comments above.... Here's an example of pricing a few years ago from an article on GBA

    "I was pleasantly surprised recently when I asked Leader Home Center in Brattleboro, Vermont, to price a number of insulation materials for a BuildingGreen report we’re revising. The contractor pricing for ComfortBoard IS came to $0.64 per board foot, compared to $0.48 per board foot for standard polyiso, $0.75 for fire-rated polyiso (Thermax), and $1.07 for XPS.

    While pricing will doubtless differ in other regions and for different quantities, the fact that ComfortBoard is in the same ballpark as these other materials is great. Even after correcting for the lower insulating value (you need more thickness of ComfortBoard to achieve R-10 than with the foam plastics), Comfortboard IS locally was more affordable than XPS: roughly $1.59 per square foot at R-10 for ComfortBoard vs. $2.14/sf @ R-10 for XPS."

    Maybe I haven't called around enough, I just haven't found anything close to those prices.. I haven't seen anything close to $1.59 sqft for R10 with comfortboard.

  2. user-2310254 | | #2


    I understand why you are focusing on mineral wool, but have you considered reclaimed rigid foam? Also, what climate zone are you in?

  3. rodrob15 | | #3

    I will be building in West Virginia (zone 5). Reclaimed rigid foam is definitely a great option, but seems hit or miss in terms of availability. Do you have any sources you've used? It doesn't need to be in West Virginia. I have a trailer so can pick up materials.... I've asked a few places I've called, and none carry reclaimed foam. I'd really only be looking for EPS too given its greener than XPS and Polyiso and its also more breathable....

    I'm really not a fan of XPS given the blowing agents and I think some of its claims are misleading. People are putting XPS below grade because of the advertised superior water resistance to EPS, but that's only true based on one specific test where foam is dunked in water. Real world studies show that EPS holds a lot less water than XPS when each is tested after its been installed for a few years. Polyiso is ok to me, but I also find the R value claims misleading and that also kind of makes me think negatively of the product (i.e. because R values go down in cold weather and degrade significantly over time)

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