On Sep 2, 3:27*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.

1 The guy says R 20 for 5.5" thats under R 4" not very good, there are
foams sold at R7 spray on for R 38, you have to shop around.

2 Polyisocyanurate board is R 7.2" so 5.5" is R39.6, it is sold in
1/2" sheets. If you look you will find an installer doing R7.2" spray
foam. But R 30 is nowhere near code in my area of Zone5 so you must
live south where heating isnt so expensive. Zone 5 optimal is around R
60, my Minimum code is R35, remember codes are minimums.