Hi everyone, I’m a longtime subscriber to FHB but this is the first time I’ve tried out the forums.
I’m going to be remodeling an attic (central Illinois area). The footprint is about 25′ wide and about 32′ feet deep w/a 12/12 pitched roof and 2×6 rafters. I know it’s important to leave an airspace between the attic insulation and the roof sheathing, however most of the rafter bays don’t actually go all the way to the peak of the roof, so the soffit->ridgevent airflow is nonexistent. Can I get by w/some kind of 4″ batts stapled into the bays (leaving about 2″ of space) and following that up by furring out the inside along w/some insulating board (similar to a basement setup)?
Thanks in advance for any advice you guys can share!
Replies
First of all, the assumption that all roofs must be vented is a myth IMHO. There's been quite a bit of research in the past 20 years showing that it's virtually impossible to evenly vent a roof in an open attic much less in a cathedral ceiling application like yours. Check out the research done at the University of Illinois by William Rose for more information.
FYI, I renovated my own attic several years ago and did not vent the roof at all over the inhabited spaces after doing the homework. No shingle curling, no moisture problems, great living space. I live in northern Illinois.
What R-value did you get w/your attic remodel? Right now I'm looking at R20 or so w/dense pack cellulose in the 2x6 rafters, possibly more w/isocynene once the sales guy gets back to me. I've seen R-49 listed as a recommended number for attic insulation, but that seems an impossible number to achieve for an attic living space. If I run the Mooney option (which I'm leaning towards atm) then I can get into the mid 20's pretty easily. R-30 might be the most I can reasonably hope to get.
This same question has been asked at least 3 times in th last 2 weeks.
Forget the vents, spray it with foam for the best results.
2nd choice, search for Mooney wall here & do that. No vents.
3rd choice no vents, dense pack cells & layer of EPS with DW over that.
FG batts are a waste of your time & money. Buy beer and pretend you are warm.
Joe H