[Greenbuilding] R12 for 3" of Roxul Comfortboard IS..

Joe Killian kaa-ajk at sonic.net
Sun May 1 07:41:28 MDT 2016

Sounds excellent.  Make those furring strips vertical for a drainage 
plane under the siding (but no barrier, want the Roxul/rockwool to 
breathe) and you've got what buildingscience.com calls the perfect wall.


On 5/1/2016 4:49 AM, John Straube wrote:
> No experience with the wall, but I have thought about this on some projects.
> A 2x4 wood stud wall filled with clay, sheathed on the outside with a highly permeable sheathing like fibreboard or exterior gypsum, would dry quickly, and be relatively quick to build (and easy to convince code officials). In your climate, the sheathed in walls would quickly weather the building in.  I doubt more than 4" of clay does mouch for you anyway at timescales of under a week.
> Then add an air and water barrier (I would prefer fluid applied over fiberboard, but even loose laid Tyvek would be decent) and 6" of rockwool, held in place with furring strips and then siding.
> In your climate, that would be a great wall thermally, would be airtight, water resistant, durable but would not meet the PassivHaus requirements (which don’t usually make sense for a project like yours, so can't see why you would want to try).
> Use not too many but great quality windows (Cascadia triples are in your neighborhood or homemade triples of wood) and a modest amount of PV will bring you into the realm of net zero, which is more meaningful than the specific PassivHaus goals in many cases.
> John Straube
> www.johnstraube.com

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