[Greenbuilding] Mold questions

[Jefro]

Hi Robert, thanks for the response

Not sure what "just don't" refers to.  Don't ventilate the crawlspace?  
Or don't use a vapor barrier under the house?  The building department 
here recommends neither insulation nor vapor barrier in a crawlspace, 
and while I was very skeptical at first I'm starting to see the logic.

Our climate isn't quite "southern humid".  Average air temp here is in 
the low 60s so we are more similar to Vancouver than to most other 
places in the US.  I agree about not using vapor barriers at all, but 
short of cutting holes in the sheathing I'm not quite sure what to do; 
that's the main reason I posted to the list.  We had originally intended 
to be building with bales and using permeable earth plasters on both 
exterior and interior, but that plan has changed considerably. 

We have been looking at cellulose because it is recycled and natural, 
but building a solidly performing house that will last a hundred years 
is much greener than using recycled materials and rebuilding every few 
decades.  I am not very familiar with Roxul but will do some research.

thanks again

Robert W. Tom wrote:
> On Mon, 28 Aug 2006 04:29:00 -0400, Jefro <jefro at jefro.net> wrote:
>
>> Mold is a big concern for us, as my wife has asthma and we both have 
>> allergies.
>>
>> - We are planning to use cellulose insulation.  Mold loves cellulose
>
>> - I am concerned about getting vapor barriers right.
>
>> (well-ventilated) crawlspace
>
> Ggggnnnaahhhhh !
>
> Sounds like a Disaster in the making, with a capital "M".
>
> A "well-ventilated crawlspace" in a humid southern (US) clime surely 
> has to be on Joe
> Lstiburek's  (a good Canadian, eh ?) "Top Ten" list of dumb things to 
> do. If not, it should be. So just don't.
>
> Similarly with the cellulose:
>
> If there are any doubts about the ability of the designers and 
> builders to detail the air barrier so that bulk moisture transport via 
> air leakage is minimised, I'd say look for some other insulation that 
> has a capacity to drain and is not susceptible to moisture. (ie Roxul 
> mineral wool)
>
> As for vapour barriers; vapour diffusion through the broad surfaces of 
> buildings never has and never will be a problem in a mild southern 
> (US) clime... so "getting the vapour barriers right" means not using 
> them.
>
> The sheathing materials (plywood) and Portland cement plasters in 
> themselves are of sufficiently low vapour permeance that they will 
> likely behave as effective vapour diffusion retarders, and possibly 
> even dangerously so.
>
> ===* ===
> Rob Tom
> Kanata, Ontario, Canada
> <archilogic at chaffyahoo dot ca>
> winnow the chaff from my edress in your reply
>
>