[GSBN] Can bale buildings be air tight?

Thu Mar 28 07:27:49 UTC 2013

ej George,
thanks for persisting on that topic.  I failed to respond, with my own 
data, shortly after Chris announced his 0.99 achievement.
That really says it all, so what more was there to say? Yes, SB can very 
very airtight, and Chris, you're the guy to do it.

But since you are still interested in collecting data, I'll offer the 
results of the one and only SB house in our area that actually was 
tested. It is in Renfrew County, just East of Algonquin Park, Ontario, 
Canada.
This house was built for Skye Faris, and completed in 2003. Since I was 
a confirmed straw bale skeptic at that time, I probably "overbuilt" it 
to the max, as I just didn't want to create a Bad Thing.
So Details were God, and we prayed daily to that ruler, while on the 
job, and it's been a warm and cozy house ever since.

In 2009, there was a series of blower door test done in our area, around 
retrofit grants, and I asked the fellow if he'd ever tested a straw bale 
structure before. He said No. But, he was so eager to see the results, 
that he did the test for free, that very afternoon.
Her story and a half house of 1050 sq. ft, using all "orphan" windows 
from salvage, tested in at 3.3 ACH.
Considering the saggy vinyl windows that were used in the place, (for 
economy reasons) it seemed like a very good out come.

Hope that adds to your statistical review.

-- 
Frank Tettemer
Living Sol ~ Building and Design
www.livingsol.com
613 756 3884

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