[GSBN] High Performance Strawbale

[Alfred von Bachmayr]

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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