[GSBN] High Performance Strawbale

[Laura]

Laura Bartels
Green Weaver Inc. 
(970) 379-6779
www.greenweaver.com
Laura at greenweaverinc.com
Sent from my phone. Please ignore typos.



Chris Magwood <chris at chrismagwood.ca> wrote:

>Hi Alfred,
>
>The creation of bale buildings that address infiltration has been my 
>main focus for the past few years of design/build, and we've got it down 
>pretty well now. Our last blower door test had 1.2 ACH/50, and 
>afterwards we realized that the plumbing stack was open! So the walls 
>and wall junctions were really tight. The house we did for Habitat for 
>Humanity last year 
>http://endeavourcentre.com/our-portfolio/habitat-for-humanity-house/ had 
>some issues around the straw/clay walls we did, but the bale walls were 
>tight and the house ended up at 2.1 ACH/50.
>
>In particular, I've been focusing on how to achieve this level of air 
>tightness without lots of yucky "product." For the bale walls, here's 
>what we do:
>
>- a strip of air barrier runs along the top edge of the wall, running 
>along the bales, under a strip of mesh, so that the barrier is covered 
>by the plaster and ties into the barrier in the ceiling. This is the 
>biggest leaky place in most bale buildings.
>- depending on the floor/foundation type, we'll use a similar strategy 
>at the bottom of the wall for wooden floor systems or good sill 
>gasketing and a caulk line on the interior and exterior edges for slabs.
>- at windows, we don't use spray foam but a light mix of hempcrete to 
>seal around the windows. Barrier strips are used here too under the 
>plaster seam.
>- electrical outlets get site-made barrier "hats" and we caulk around 
>the wire once it's been put through the barrier. We've also used the 
>plastic "R-2000" electrical boxes but we don't trust the neoprene seal 
>for the wire and caulk these too.
>
>It's really pretty darn easy to get a bale wall air tight. The beauty of 
>the continuous plaster is that there aren't that many seams, and the 
>ones that do exist are easy to predict and do something about! It's a 
>much less difficult and troublesome process than making a frame house 
>air tight.
>
>As a side note, the prefab panels we've been making have these barrier 
>"tails" already embedded and ready for joining to other building elements.
>
>The insulation value question is about to come and haunt us in Ontario 
>too. In January, the codes here raise the required R-values and I'm sure 
>we'll be facing some questions from plans reviewers who use the lowest 
>possible figures that are out there. I'm hoping that we can set up some 
>full-scale testing here to get good figures on a full wall panel, and of 
>course we'll share any results we get.
>
>Chris "Starving for Air" Magwood
>
>On 11-10-03 11:49 AM, Alfred von Bachmayr wrote:
>>
>> Greetings all,
>>
>> Thank you for including me in this elite group of building scholars.
>>
>> I wanted to get feedback on some performance aspects of strawbale 
>> building that I have been confronted with by energy modeling and 
>> regulatory entities that question its thermal performance.  This 
>> resistance appeared when I contracted a Hers rater along with 
>> mechanical engineers who, in generating thermal models of a strawbale 
>> building I had designed, consistently gave it low ratings for R-value 
>> and infiltration.  In researching the R-value they had given to the 
>> walls, I found that from the resources they had found, the value was 
>> somewhere between R-23 and R-27.  I got a copy of the newly proposed 
>> International Green Conservation Code and found they rated bales laid 
>> flat at R-1.3 per inch and on edge R-2.  That equates to R-23.4 for 
>> flat bales (2 string) and R-28 for bales (2-string) on edge.  I don't 
>> think this gives and accurate performance prediction of  the 
>> building.  In addition they considered the buildings to have high 
>> infiltration losses because of their opinion that they cannot be 
>> tightly sealed.  Their models indicated that the building could not be 
>> considered high performance due to the use of the straw thereby making 
>> my job of getting the building to the required Hers rating value much 
>> more difficult.  I am thinking I am not alone in this problem.
>>
>> This made me realize that we need to generate more convincing 
>> documentation as to the performance and design detailing of straw 
>> buildings.  There appears to be little resources out there that 
>> engineering professionals access that address the infiltration and 
>> insulation values of straw.  This is important because without a 
>> sufficient HERS rating and a positive blower door test (now being 
>> required in many jurisdictions) a permit and/or a CO will not be issued.
>>
>> What I would like to hear from you all is the location of resources 
>> documenting tight houses out of straw (like the passive houses) and 
>> specific techniques you have used to tightly seal up straw buildings. 
>>  Specifically what techniques have you used to seal around the windows 
>> and doors, at the bottom and top of the walls and at penetrations of 
>> the interior finish skins for electrical boxes.  Are there buildings 
>> out there that have gotten their HHI ratings down below 2 BTU/SF/DD?  
>> If so what techniques did they use and what insulation and 
>> infiltration rates were used?
>>
>> Thank you for your help.
>>
>> Saludos,
>>
>> Alfred
>>
>> VON BACHMAYR ARCHITECTS LLC
>>
>> 1406 Bishops Lodge Rd.
>>
>> Santa Fe, NM 87506
>>
>> 505-989-7000
>>
>> 505-984-1479     fax
>>
>> 505-470-6141     mobile
>>
>> vbarch at comcast.net
>>
>>
>>
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>
>-- 
>www.chrismagwood.ca
>www.endeavourcentre.org
>
>
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