On Sep 2, 4:27*pm, the_tool_man wrote:
Hi all:

I'm finally finishing that bonus room project, and am investigating
insulation options for the cathedral ceiling. *The roof structure is
standard 2x6 rafters on 16" centers with OSB sheathing and shingles
above. *I need to achieve R30, and would like to do so without loosing
much headroom. *From what I have learned, this will almost certainly
require a foam insulation of some kind. *I have investigated three
options:

1: A local installer of Icynene foam (trade name for a polyurethane
foam). *He has a minimum $2000 charge, and wants $2500 to do the whole
room (ceiling, walls, floor, stairwell). *He claims an installed R-
value of 20, but claims that because it is foamed in place, the air
permiability is virtually nonexistant, so the "effective R value" is
much higher.

2: Spray foam kits can be ordered, but are very expensive. *Tiger Foam
sells a 600 bdft kit for $630, but I would need just over 1300 bdft of
foam just for the rafters (1 bdft = 1 sq ft x 1 in thick). *Again,
almost $2000. *This does not include walls, floor, or stairwell, and I
would have to do the work.

3: Use Dow Thermax precast polyisocyanruate foam, available locally in
2" thickness. *Enough to do my ceiling would be just shy of $1000, and
would require a 3/4" layer of foam on the underside of the rafters to
achieve R30. *This would require a lot of cutting and fitting of 2
layers of foam between the rafters and a third below. *The walls,
floor and stairwell would be insulated conventionally at a cost of
about $400 in materials. *Thermax is available in 4" thickness, but
not locally, and I would have to order a truckload to get any, so 2
layers of 2" will have to do if I go this route.

Option 2 is definately out. *Right now, I am leaning toward option 3,
as it is the least expensive (yes, I am ignoring the value of my time
to do the install). *I am wondering what else is out there. *I find it
hard to believe that with all the green building movement going on,
there aren't more options for acheiving high R-per-inch. *What other
options are out there?

Thanks in advance,
John.

Just a few random thoughts to confuse you.

First, if you're now 'finishing' your 'bonus room' (and how I hate
that term); why are you only insulating it now???

Second, if you have 2x6s, you shouldn't be putting 5.5" of insulation
in them because you need some space on the outside of the insulation
for air to circulate. If you go with a spray-on, I think you'll need
to have them install those vents to keep the air flowing.