[GSBN] [Strawbale] Mycotoxins (GSBN Digest, Vol 35, Issue 20)

Sat Mar 26 00:08:38 UTC 2011

If I were them I would not have a great deal of trust in the architect.

However, in response to Rob, /stachybotrys atra /is not the fungal 
species that I would be concerned about at the design stage.  If local 
relative humidity gets up to the levels where /S.Atra/ can thrive, then 
other problems will have occurred too.  And the climate in southwest 
England (where I used to live) is much more humid than that in eastern 
Canada where Rob's examples come from, so humidity issues need more 
careful attention.

The mould species to pay attention to in design are the xerophilic 
primary colonisers - primarily /eurotium /spp and /aspergillus /spp.   
The most xerophilic appears to be /aspergillus repens/: at 20degC its 
mycelia can grow at about 75% rh - higher rh values are required at both 
lower and higher temperatures; and spore germination also requires 
higher rh values.

My own findings - based on computer modelling - indicate that 
properly-designed, properly-detailed, properly-constructed strawbale 
buildings are safe from /aspergillus repens/ growth in a humid temperate 
maritime climate, provided that (i) relative humidity indoors is 
controlled below 70%, and (ii) high vapour transmissivity plasters and 
renders are used (i.e. clay and lime plasters, preferably with no use of 
Portland cement whatsoever).  I think that most (maybe all) experienced 
sb builders in that climate zone in Europe would confirm this from 
practical experience.

Mark

On 2011:03:25 12:44, RT wrote:
> On Thu, 24 Mar 2011 13:00:02 -0400, <gsbn-request at greenbuilder.com> 
> wrote:
>> Date: Thu, 24 Mar 2011 07:56:02 -0400
>> From: carolatkn
>> Subject: [GSBN]  Mycotoxins
>
>>
>> I recently met a young couple wanting to build a new home on their 
>> family farm in south west England. They had been told by their 
>> architect that they should discount straw bale immediately as they 
>> would be certain to die from exposure to mycotoxins!
>
>> My initial response is that if the straw is baled and kept dry there 
>> will be few moulds anyway and crack free plaster would prevent any 
>> that were present making their way into the living space.
>
> [BIG <snip>]
> for full text of message and thread see:
> http://greenbuilder.com/pipermail/gsbn/2011q1/001379.html
>
> Sometime within the past 10 years (+/-) the City of Gatineau (in the 
> Province of Quebec, Canada (just across the river from Ottawa of which 
> the former City of Kanata is now a part)), wanted to enact a by-law to 
> ban the use of straw bales for making buildings in that city.
>
> The City's reason for wanting to do so was because of moisture-related 
> problems with at least one SB house (a two-storey dwelling, exterior 
> plaster fully exposed to rain wetting) in that city.
>
> A woman who spent time in that house and another SB large building 
> (with known wet SB issues) elsewhere in the province of Quebec 
> reported that the buildings made her sick.
>
> Don Fugler was one who kept files on these before he retired from 
> CMHC.  I don't know if Don was able to acquire any funding to have 
> forensic testing done on the affected buildings as he did for the report:
>
>    "Pilot Study of Moisture Control in Stuccoed Straw Bale Walls" 
> (June 1997)
>
> where the walls and floors of SB buildings that had been occupied for 
> ~10 years were cut into, straw samples taken/inspected and moisture 
> paths identified.
>
> That report, which includes nice colour photographs of 
> mould-deteriorated straw should still be available from CMHC.      
> http://cmhc.ca/
>
> If not, I'd consider scanning it and putting it into a PDF if 
> sufficient demand warrants (and if CMHC gives its permission).
>
> As with any other moisture-susceptible cellulosic material that is 
> allowed to get wet and not provided with the means to dry properly, 
> one can expect microbial activity to occur.
>
> It was mentioned by a senior bureaucrat at Health Canada (at least 15 
> years ago) that straw is an ideal host for Stachybotrys atra  
> (Stachybotrys chartarum) , a black mould that was a prime suspect in 
> infant deaths ( pulmonary hemorrhaging).
>
> True, SA needs humidity levels of ~90% in order to develop but that 
> would not be out of the question in a SBH built in a Cold Climate 
> region where insufficient attention was paid to air-sealing and/or 
> keeping rain off of exterior plaster and/or faulty flashing details 
> and/or about a half dozen other reasons.
>
> Bottom line: The fears expressed by the Brit architect may be 
> over-stated but not completely off-base, probably a hysteria borne of 
> seeing bits and pieces of messages like this one, out of context.
>
>
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