[GSBN] Straw-Bale Blower Door and Infrared Test Results

[ejgeorge at riseup.net]

Hi David and Anni,

Sorry I didn't have a chance to respond sooner. Thanks for sharing the  
test results especially all the infrared photos - some of which I had  
questions about.

As one might expect, it appears most thermal breaks/leakage areas are  
at shell transitions (window/door frames, studded corners, foundation,  
wall to ceiling, etc). There are a few envelope breaks in walls in  
some of the pictures, but I wasn't sure which ones were wood framed vs  
bales:

photo 7 shows a light fixture beside a door with virtually no thermal  
compromise at the light box
photo 8 meanwhile shows an outlet near a door that is clearly leaking
and photos 8 & 9 show the pipe penetration which is mentioned

Are the walls in these particular photos bale walls or wood framed?  
And if they are bale walls, how were these elements installed  
into/through the wall and how were they detailed?

Air leakage detailing has become a big topic at our Natural Builders  
Northeast (US) gatherings the past couple years and we've started  
gathering blower door data on straw bale houses in our region that  
have been tested.

There's info on around 20 buildings (but incomplete data on several)  
built from 1995 through 2009. They ranged in size from just under  
3,000 to almost 40,000 cubic feet. The tightest so far was a 11,516  
cubic foot, load bearing home built in 2009 by Ben Simpson/Growing  
Places (CFM50=475, ACH50=2). Otherwise:

CFM50's ranged from 344 to 1909, averaging around 1260
ACH50's ranged from 2 to 7.16 with an average of 4.69
ACHnatural (for the few that included it) were from .17 to .54
unfortunately, none of the tests included the CFM50/sf metric  
mentioned by John S. to compare overall envelope leakiness. I'd be  
curious to work that out on a few of them some day, although as John  
also points out, in the end it's the CFM50 number that best compares  
whole building performance.

In general, most of these builders were aiming for something that  
would hopefully meet EnergyStar (ACHnat less than .35) without  
requiring mechanical ventilation (via ASHRAE - depends on several  
variables, but roughly ~.25-.35 for most these homes).

Not surprisingly, as builders have developed more details for  
problematic areas, homes have gotten tighter - of the 8 houses  
included built since 2007,
average cfm50=1040  and average ACH50= 3.61. At our last gathering, a  
couple builders seemed keen to see how much tighter they can get, but  
I don't think anyone was aiming for PH extremes. Hopefully we'll have  
more numbers to collect at our upcoming gathering.

Thanks again.

ej

p.s. if anyone knows of blower door data for other sb buildings in our  
region (NorthEast US - basically New England & New York) or similar  
cold climates (zones 5, 6, & 7), I'd be happy to add it to our  
database - thanks!