[Greenbuilding] Mold questions

[Chris Green]

Jefro wrote:
> Regarding mold <snip>  When you see it in fiberglass, do you see it in the glass 
> itself, or in the paper backing?
>   
I have worked on some renovation projects and found black, moldy 
fiberglass batts. It is my belief that the fg batts act like a lint 
filter, capturing dust and dirt that the air flow inside the cavities 
bring in and move around. That's just an opinion based on observation, 
but it is this soil which, once some moisture is present, acts as a 
growing medium for the mold and yes, it does grow on the 'glass fibers-- 
like mold in a petrie dish.

I believe that Roxul mineral wool is much less prone to this. For one 
thing, it's stiffer and won't sag when it becomes wet. This means a 
lower likelihood of convective air flows inside the cavities, which is 
possible if the pink fg sags away from the sheeting.
Roxul is also a lot denser and fills the cavity much better. As a bonus, 
because it's denser, the stated R-value of the product is 10% higher ( 
R-22.5 as opposed to R-20 for the 6" batts, all other things being equal.)

Lawrence Lile has mentioned that he caulks the stud/ sheeting 
connections and the horizontal spaces between the sheeting to prevent 
moisture infiltration.
Another way to do this, add some insulation, and cut down on all that 
caulking would be to install inuslboard with the aluminum foil coating 
on it. The foam panels can cover the joints between the sheeting if 
offset by, say, 12".  Being foam, the moisture won't pass through the 
panels. The joints between the foam panels can be taped over with Tuck 
Tape or some such.
In case it isn't obvious, the foil side faces the inside of the building 
in order to reflect the heat back into the wall cavity.
The house I am working on now has insulboard over top real plywood 
sheeting this way, and will have boron treated cellulose in the stud 
cavities  The owner is a successful insulation contractor in our area 
and everything will be insulated to a much higher level than normal for 
this area.
In handling the sheets of foam these past few days, I've noticed the sun 
reflects off the metal foil quite nicely, thank you, and with air temps 
at about 37C yesterday, the extra heat felt like I was in 50C+ conditions...

Taken together, a drier and hotter wall system should reduce the 
potential for mold growth.
I think. Someone kindly correct me on that if I'm wrong.

Cheers,

Chris Green.