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

John Straube jfstraube at gmail.com
Sun May 1 05:49:11 MDT 2016

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

-----Original Message-----
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Koehn Chris
Sent: April 30, 2016 15:48
To: greenbuilding at lists.bioenergylists.org
Subject: Re: [Greenbuilding] R12 for 3" of Roxul Comfortboard IS..

Following this discussion with some interest. Beginning stages of designing a small home with the aim of achieving Passive House using (mostly) natural- or healthy- materials.
We built a house recently using 12” deep Larsen trusses with full “chip and slip” infill with clay plaster finishes. Great material, very labour intensive, dries slowly, not the highest insulative values (a problem with Passive House).
So we’re keen to experiment with Roxul board (or other?) for a chunk of the wall, maintaining a 4-6” layer of chip and slip, presumably interior, to reap the hygroscopic benefits of the clay.

Any thoughts or experiences with such a wall?

We’re on Vancouver Island, so pretty low Delta T (at least for Canada) but nearly as many heating degree days as colder climes back east.


Chris Koehn

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