[GSBN] Cellulose in unvented roof

[timok]

Hi All, 

I know this question isn't exactly straw bale but, it is a topic about which 
reasonably good builders disagree. and we've come accross a county that 
wants more legitimate reasoning than we're discovering on our end soooo... 

Do any of you have an U.S. building code accepted report or testing on the 
use of cellulose in an unvented roof cavity. we have a roof design that's 
almost impossible to vent and it's pre-insulated with cellulose so we can't 
back up now. the best we've come up with is an supplement to the 2007 IRC 
that allows Air permeable insulation to be used with the addition of R-15 
rigid insulation on top as a condensation control. though this sounds like a 
good idea thermally and long term, there is already r-42 in the roof and the 
facia is bought, so I'd love to find a few reports that back the concept 
thoroughly enough to make our case stick. 

of course I'm open to being schooled by the great wizards of building 
science should my thinking be flawed about the benefits of an unvented roof 
cavity. but thermally, and to protect against fire flow up and into the 
eve's, I believe we are better vent free and I think the condensation is 
better handled in drain planes below the roofing and in not drawing extraw 
moisture into the roof through the eve's. and from my humble interpretation 
of John Straube last CASBA presentation there would have to be enough air 
pressure to suck small children off of the side walk in order to move air 
through the small cavities significantly enough to matter; for moisture or 
heat exhaust, was my interpretation. 

just trying to build the best buildings we can, 

from the firey hills of Mendocino county, California...where we would traid 
a lot for some condensation, i extend my thanks for your help with this 
detail 

tim 

 

Tim Owen-Kennedy
Vital Systems
Box 751, Ukiah, CA 95482
www.vitalsystems.net