[GSBN] Can bale buildings be air tight?

[John Straube]

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 50 worth.  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 50 look 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.

On 12-11-13 7:13 AM, Chris Magwood wrote:
> Hi all!
>
> Maybe the question of whether or not a bale building can be built air
> tight hasn't been keeping you all awake at night, but it's caused Jen
> and I some long evenings of thought and lots of detail drawings on
> our plans! Maybe that's just what keeps northerners warm at night...
>
> We've been honing in on good results over the past couple of years,
> and this year we finally nailed it (but didn't put a nail through
> it... that would have been counter-productive). We just did a blower
> door test on our most recent project and ended up with a result of
> 0.99 ACH50. That's approaching the PassiveHaus goal of 0.6, and we
> realized after the test that we hadn't covered up the open sump pit
> in the basement, so we may actually get to PH levels with the final
> test.
>
> The building has a mix of site-built, clay plastered walls and
> prefabricated, lime/cement plastered walls. We've long used a system
> that uses a flexible air barrier (house-wrap type membrane) at the
> edges of the walls where the plaster will meet ceiling, floor and
> intersecting walls. The membrane wraps down behind the plaster by 3-4
> inches. What was interesting with this building was to find that in
> some areas that detail worked very well, and in others it didn't help
> much at all.
>
> What this tells us is that unprotected plastered edges leak... a lot!
> Our first blower test helped us discover that some of these seams
> were leaky. One leaky wall accounted for a shocking 74 square inches
> of leakage! By eye, it just looked like  the usual plaster shrinkage
> around the edge of the wall, maybe 1/8 inch. But multiply that around
> an entire home and it's no wonder that many bale buildings under
> perform in blower door tests. You can see photos of these areas on
> our project blog at
> http://endeavourcentre.org/2012/11/blower-door-test-1/
>
> What we don't know is why some areas stayed tight and others didn't.
> Our best guess is that it can come down to quality of work. How long
> was the barrier tail left? How well was the mesh installed over it?
> How vigorously was the plaster pushed into the mesh? The plaster
> pulling away at the edge as it shrinks also seems to cause some
> slight bending of the skin inward, taking it away from the barrier.
>
> One good take-away from this project is about the beauty of clay
> plasters. The leaky edges of the clay plastered walls were relatively
> easy to address... moisten the edges a bit and squeeze in more clay
> mix. Everything bonds together and the seams went from very leaky to
> completely tight!
>
> Now, if anybody happens to ask if them there bale houses can be air
> tight, it's possible to answer yes.
>
> Cheers,
>
> Chris
>

-- 
Prof. John Straube, Ph.D., P.Eng.
Faculty of Engineering
Dept of Civil Engineering / School of Architecture

www.buildingscience.com