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Rockboard [mineral wool] or polyiso?

I'm planning a new house. I've been thinking in terms of 2 3/4" of polyiso on the exterior of the walls. However, I'm now thinking that dense rockwool board *might* be better at least from the standpoint of the wall being able to dry to both the outside & inside. I kinow I'd be giving up some r value, but perhaps I could just up the thickness ? I'm in climate zone 4 Western NC in the mountains. Probably using zip sheating under either insulation board.

Asked by Roy Goodwin
Posted Thu, 06/12/2014 - 09:08
Edited Thu, 06/12/2014 - 10:03

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2 Answers

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1.
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Roy,
To read the accounts of two projects with mineral wool insulation on the exterior side of the wall sheathing, check out these articles:

Installing Roxul Mineral Wool on Exterior Walls

Wrapping an Older House with Rock Wool Insulation

You might also want to read:

Installing Mineral Wool Insulation Over Exterior Wall Sheathing

Answered by Martin Holladay, GBA Advisor
Posted Thu, 06/12/2014 - 10:02

2.
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Roy,
I'm in Upstate SC and did exactly that on our new house. We put 2" Roxul Rockboard wrapping the entire exterior. I chose Rockboard, because I could not easily get Comfortboard. The big box stores have to order Roxul Comfortboard in large pallets and wait for a full load before they order. They estimated 6 weeks for a shipment. I got Rockboard easily from ATS Acoustics online in less than a week. I think Rockboard and Comfortboard are the same product. Here is the GBA post talking about the 2 products:
http://www.greenbuildingadvisor.com/community/forum/green-products-and-m...

Patrick Walshe's blog, http://agreenhearth.com, has a good discussion on using mineral wool.

My blog has some information as well. http://greenvillegreen.blogspot.com/2013/10/cozy-mineral-wool-sweater-on.... You could hit the mineral wool insulation under labels and see the posts on how we used the Roxul.

Answered by Lucy Foxworth
Posted Thu, 06/12/2014 - 14:20
Edited Thu, 06/12/2014 - 14:21.

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