[Greenbuilding] spray foam/fiberglas

Bob Klahn Home-NRG at dnaco.net
Sat May 14 18:34:34 PDT 2011

When you say the spaces are irregular, is it safe to assume you mean the 
spacing between the rafters.  Trimming the batts narrower to fit the 
non-standard cavities can be finicky work but is possible.  The sprayed 
foam is also likely to be an irregular surface, but the batts will 
conform to some extent.  Both complications would discourage me from 
using batts, even though I mentioned that earlier as an option.

I agree that installing a good, sealed,  air barrier (taped and mudded 
drywall for example - just avoid plastic) before installing the t&g 
ceiling is essential.  The primary source of moisture is from the inside 
air; water from a roof leak is always a long-term possibility but 
interior humidity is a constant pressure.

I'd think about blowing the space with "spider blown" fiberglass after 
the air barrier is in place, then sealing the access openings.

Bob Klahn

On 5/10/2011 9:18 PM, tom at honeychrome.com wrote:
> Thanks Bob and Ron for the responses.  Yeah, when I had the foam 
> installed I should have told them to fill the cavities completely and 
> paid the price, but they were 'the experts' and told me it wasn't 
> worth it.  It didn't really make sense to me at the time, but I didn't 
> follow through.  I don't plan on selling this house, so resale and 
> short-term investment recovery isn't a priority.  I haven't installed 
> the ceiling yet, so I can still add insulation before I put the 
> paneling up.  The ceiling is t&g pine boards, so I could install most 
> of it up to the peak and blow in cellulose from the top, or put in 
> fiberglas bats, though the spaces are somewhat irregular.  Seems like 
> the cel. might be the better option.  But there is also the moisture 
> issue.  Even pretty well sealed, it is rather dry in the house in the 
> winter (wood-stove heated) and the roof isn't vented (which is why 
> blown-in closed cell was installed).  Will filling in the space left 
> with fiberglas or cellulose create a situation where moisture can collect?
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