[GSBN] Can bale buildings be air tight?

[ejgeorge at riseup.net]

A much delayed response on the airtightness topic, but one that helps  
answer Derek's pondering of how often a custom home hits 3.15 or  
better (at least custom straw bale homes in the Northeast US). Aaron  
is presenting at a "Low Energy Homes" Symposium next weekend, and was  
looking for similar information so I went through some straw bale  
blower door test results gathered  by various members (Jay Walsh,  
Jacob Deva Rascusin, and myself) of NBNE over the last 7 or so years  
and compared groups of data over time. I did discard numbers for a  
couple of structures that had major gaps at testing making their  
results of little value (one hadn't covered the opening of an  
uninstalled window, and one was an owner built home with numerous and  
volumnious unfinished details).

The first blower door test I'm aware of in the Northeast US was in  
2005. There are some older straw bale houses included (built between  
1995-2005) but these were all tested well after construction (sometime  
in the late 2000's).

Homes built 1995-2006 (6 total), had an average ACH50 of 6.12
As far as I'm aware, these were all single blower door tests, most  
done well after completion. I believe all but one met US Energy Star  
rating for the time (<.5 ACHnat).

Homes built 2006-2007 (8 total), had an average ACH50 of 4.71
Most of these were single tests again, but now done near or at  
completion. There was a growing awareness of the importance of  
air-sealing by this time and various methods attempted to mitigate  
obvious leakage areas. Many of these homes may have had additional air  
sealing done after their test, but other than one built in PA by a  
home performance company (Envinity) I don't know if any did a second  
test (Envinity's final result was 3.32). I believe all of these homes  
met the US Energy Star rating.

Homes built 2008-2009 (6 total), had an average ACH50 of 3.91
Again most were single tests done at/near completion. The tightest was  
a load-bearing home built by Ben Simpson with an ACH50 of 2.0.

Homes built 2010-2011 (3 total), had an average ACH50 of 3.24
Still mostly single tests done near/at completion. Of interest, a  
GreenBuildingAdvisor article written in 2010 quoted: "ACH50 of 5 to 6  
is considered tight", which I guess makes these homes "very tight"  
though not quite "super tight" like Passive House or Canadian R-2000  
requirements.

And that brings us to 2012-2013. The only two houses I have data on so  
far is yours (3.15) and Aaron's latest (2.27). Which continues the  
downward trend to an average of 2.71 ACH50. Aaron did not bother to do  
a final test, but you said you got .99 on your second. Curious to hear  
your final numbers. I'm also cc'ing to the NBNE list since I'm sure  
more of them have numbers from last year to share and I know some of  
the Vermonters have been gunning for PH too...

All for now,

ej

ej George, CSBA
Tugley Wood Timberframing
6301 Searsburg Road
Trumansburg, NY 14886
tugleywood.com





Quoting Derek Roff <derek at unm.edu>:

> Congratulations, Chris!  This is an excellent result, and very  
> useful data on the performance potential of a well-detailed  
> strawbale building.  Keep us posted on what changes you come up  
> with, to decrease the variability in your air sealing details.
>
> In your blog, in reference to your initial 3.15 ACH50 test result on  
> this building, you say, "We had drawn careful details at the  
> planning stage and spent a lot of time and energy on site making  
> sure those details were well executed, and still didn't get a great  
> first result."  I'm thinking that 3.15 ACH50, too, is a great result  
> for the first test of a custom built home.  I don't really know what  
> the average result is for the first blower door test on a home, but  
> the case studies of high-performance homes that I have read tell a  
> story similar to yours- the first test shows more leakage than  
> hoped, through problem areas that have to be corrected.  I wonder if  
> John or Bruce or anyone else could venture an opinion on what  
> percentage of the time a custom builder hits 3.15 ACH50 or better on  
> the first test of a new home.  There certainly aren't many who can  
> hit .99 ACH50 on the second test.
>
> Best wishes,
> Derek
>
>
> On Nov 13, 2012, at 5:13 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
>>
>> --
>> Chris Magwood
>> Director, Endeavour Centre
>> www.endeavourcentre.org
>
>
> Derek Roff
> derek at unm.edu
>
>
>
>
>