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

Fri Dec 24 16:04:31 UTC 2010

There is no doubt that SB can meet the 0.6 standard. To do so requires attention to sealing ALL the joints.  Even one crack 1/8" long, hidden behind baseboards, window trim, intersection walls etc that is maybe 30 or 40 ft long, will essentially mean you meet it.
However, the question should be "Why would we meet 0.6 ACH at 50".  
The metric is questionable (cfm50/sf is better although the industry is only now shifting away) and that 0.6 target is totally arbitrary.
Why 0.6? Why not 0.5, 1.0 or 1.5 or 2.
The PH people chose the target based on flawed logic (condensation control is apparently the reason) and in many climates it is insane to expend too much effort to get to 0.6.
In the cold climate anecdotal experience of Canada, houses over about 3 ACH at 50 tend to have a risk of interstitial condensation. Rates over about 5 or 6 tend to be dry.  houses under 2 ACH  tend to perform quite well and only gross local errors cause condensation problems.  When the rate falls under 1.5 we note problems with high winter RH.  This is all just rough numbers but is based on a lot of houses and a lot of people in Zones 5, 6 and 7.
Depending on your energy goals and climate, you might want to get lower than 2 at 50.  BSC targets 0.1 cfm50/sf for very low energy / Net Zero houses in cold climates and hot-humid climates.  But some of the production builders we work with have reduced their fleets to under 2.5 with the occasional one at 1.2 or, and find no problems (except the need for mechanical ventilation and controlling high winter RH via using HRVs not ERVs).  In milder Zone 3 and 4 climates of the south east, getting the houses under 3 has been remarkable for improving almost all aspects of performance.

If you can get the house to 0.6 for no cost, by all means do so (and of course, this means you cant use normal range hoods in small homes, as they will extract 200 cfm + and may cause odd problems).  In my experience, airtightness costs money in terms of supervision, inspection, testing and a small amount of materials.  There is a tremendous benefit to getting as tight as David did on his house. And it would be worth hundreds of dollars more to cut it in half.  But would it be worth it to cut it to 1/8 at the cost of thousands.  I think not: better bang for buck is a small HRV, or an upgraded window.

John

On 2010-12-24, at 9:57 AM, Dan Smith wrote:

> David, that's about what I thought, what do you think about the likelihood of  bale walls meeting the 0.6 standard?
> Dan
> .......................................................
> Dan Smith 
> Principal - DSA Architects
> 1107 Virginia St.
> Berkeley, CA 94702
> 510.526.1935 x101
> 510.526.1961 fax
> dan at dsaarch.com
> www.dsaarch.com
> 
> On Dec 23, 2010, at 11:27 PM, David Arkin, AIA wrote:
> 
> Hi Dan, David E.:
> 
> Sierra Energy Professionals (SEP) say:
>> When the house pressure was at a 50 Pa difference relative to the exterior, the flow of
>> air infiltrating from outside into the building envelope was measured to be 617 cubic
>> feet per minute (CFM).
> 
> Based on "9592 cf house", 617 CFM = 37,020 CF/hour, or 3.8 times the volume of the house:
> 
> Flow @ 50 Pa	Air changes per hour (ACH) @ 50 Pa
> 617 CFM		3.8
> 
> If the house were tighter:
> 160 CFM		1.0 (probably about what John's house is)
> 96 CFM 			0.6 (Passive House (PH) certification threshold)
> 
> So house is 6.4x leakier than PH threshold.  We've done a passive house project since this one, but none bale ... yet. 
> 
> However, this is an off-grid home, with a combined passive and active hot water heating system, storing heat in an insulated sand bed, with electricity from a photovoltaic system.  So we're wasting some of that free energy from the sun ... I think we can live with that!
> 
> John, it's our 'typical' system of 14" I-joists at 7' to 10' on center, with 3-string rice bales on edge, PISE finish.  
> 
> More cheer to y'all,
> 
> David A.
> 
> On Dec 23, 2010, at 9:42 PM, Dan Smith wrote:
> 
>> David and Anni, thanks for sharing this, it is a treat.
>> 
>> What's the air change per hour at 50 Pa?
>> 
>> Happy Holidays,
>> Dan
>> .......................................................
>> Dan Smith
>> Principal - DSA Architects
>> 1107 Virginia St.
>> Berkeley, CA 94702
>> 510.526.1935 x101
>> 510.526.1961 fax
>> dan at dsaarch.com
>> www.dsaarch.com
>> 
>> On Dec 23, 2010, at 2:48 PM, David Arkin, AIA wrote:
>> 
>> Hello Fello Baleos Worldwide:
>> 
>> Since this list is particularly alive today, I'm taking the opportunity to share a Christmas treat.
>> 
>> I attach here (gosh, can I attach to this list?) a report on a Blower Door and Infrared Camera test done on a 900 sq. ft. (85 sq. meter) home in the foothills of the Sierra Nevada mountains.
>> 
>> In particular, dig this quote from Michael Ukraine of Sierra Energy Professionals:  "Any doubts that I had about straw bale or SIP construction are thouroughly gone after conducting these tests.  This is definitely the tightest and best insulated house I have ever tested."
>> 
>> The photos are quite illustrative, but certainly say that the bale walls in no way constitute a weak link in a tight or thermally superior building.  Don't ever let anyone try to tell you otherwise.  We raise a glass to y'all, and wish you an excellent New Year!
>> 
>> David and Anni
>> 
>> 
>> <Straw Bale House Photos 2010-10-18.pdf>
>> *  *  *  *  *
> 
> 
> *  *  *  *  *
> Arkin Tilt Architects
> Ecological Planning & Design
> 
> David Arkin, AIA, Architect
> LEED Accredited Professional
> CA #C22459/NV #5030
> 
> 1101 8th St. #180, Berkeley, CA  94710
> 510/528-9830
> www.arkintilt.com
> 
> "There is no way to peace. Peace is the way."
> — A. J. Muste 
> 
> 
> 
> 
> 
> 
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John Straube
www.BuildingScience.com

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