[GSBN] Can bale buildings be air tight?

Tue Nov 13 17:02:20 UTC 2012

Congrats Chris!! great to hear about all your great projects when you were
here, thanks again for coming, hope to visit up there someday!   Given this
thread, thought I would post that we just did our final test on our straw
bale passive house here in Boulder, Colorado.  We used a typical 10 ml
plastic vapor/radon retarder under the slab, Huber Zip System sheathing on
the roof which was taped down onto the box beam, and NHL plaster on the
walls.  The result was about .5ACH50.  The windows we used were tiple pane,
aluminum clad wood insulated Zola European windows (R11.36 cog, .5SHGC, R
6.31 frames) with zip tape to the solid wood bucks on the interior.  we are
now using Siga swiss tapes instead on the interior.

 The problems we found in air tightness were at the foundation joint and
several lighting penetrations that did not repair the air barrier after
being installed - in the future, we will gasket this under the plaster
J-strip so there is not air leakage between the plastic vapor barrier under
slab/walls and the end of the plaster.  Otherwise, I found the lime plaster
to be virtually airtight.  We tested a 2500 sf straw bale house with
vaulted ceilings, at 190CFM at 50.  It was not the plaster that appeared to be
leaking, but the joints where plaster went to other materials.  I am
convinced our earth plaster projects will perform just as well.  I am very
interested in building a typical 2x4 frame building with wood diagonal 1x
sheathing and then a continuous air barrier of burlap and clay plaster for
the air barrier with a 14" bales on edge wrap and may have a project next
year in this fashion.  I have been inspired by the Austrian passive house
straw bale wrap over cross laminated timber -if you haven't seen it:
www.s-house.at

On Tue, Nov 13, 2012 at 8:07 AM, Chris Magwood <chris at endeavourcentre.org>wrote:

> Thanks all!
>
> John, it's good to hear that the range to aim for is between 1-2 ACH at 50.I wasn't sure where the Passive House number came from, but I was
> attempting to get there just because I've talked to so many PHers who have
> told me there's no way to get there with bale walls, and especially not
> with clay plasters. But if we're in the right zone to be a good low energy
> house, then I'm happy with that!
>
> Chris
>
>
> On 12-11-13 8:02 AM, John Straube wrote:
>
>> Well done Chris!
>> Although it seemed possible in theory (at least I always said so) it is
>> great to get some real confirmation to be definitive.
>> Getting to 1 ACH at 50 is a real accomplishment in any housing type.
>> A tiny bit of air will likely leak through some earth plasters
>> (especially if they have straw in them) as we now have found that a tiny
>> bit of air leaks through some plywood and OSB. Maybe 0.2 or or 0.3 ACH at 50worth.  This is not really a performance issue, but it happens.
>> It is hard to get to 1 ACH at 50 without really good windows, so you likely
>> have those (casements in Canada tend to be good, double hungs in the US are
>> routinely leaky).
>> It is also important to remember that there is nothing magic about
>> 0.6ACH at 50, it is just a number someone picked.  While tighter is always
>> better, as I speak to more people at the edge of advanced housing and they
>> gain experience the more it seems that numbers between 1 to 2 ACH at 50look like a good spot to be.  There is almost no benefit to going from 1
>> down to 0.5 and there starts to be some odd effects (like challenges with
>> exhaust range hoods, bath fans etc) as we get to the 0.2 to 0.6 range
>> (effects we have learned more about as people target those numbers).
>> Suffice it to say, you have shown that you get as tight as needed for a
>> low-energy, healthy and comfortable home, even in very cold places.
>>
>>
> --
> Chris Magwood
> Director, Endeavour Centre
> www.endeavourcentre.org
>
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-- 
*Brian Andrew Fuentes, AIA, Certified Passive House Consultant*
*fuentesdesign | natural architecture*

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