insulation batts, blankets & other ?'s ...

[flipper]

in my garage conversion, i'm laying insulation on the unused attic floor; ie, right on the flat plywood flooring, not in b/ joists. i can't get insulation blanket around here in r30, so i'm limited to 15" and 24" width batts x 48" long. the cost of 15" suits my total-sq-foot needs better, so i'd like to get it; but will more seam connections with 15" result in less insulating power?

also: around here, neither lowes nor HD stock r13 in the 24" width. they don't stock it and say they can't get it. i thought 24" was as standard a width as 15". Is that not so?

thanks

ps: cross posted this to one other logical ng.

[robo hippy]

I was looking into insulating the ceiling in my pole barn shop. The purchase price for the insulation from the local Ace Hardware store was about $600. I called an insulating company, and got a price of $650 for insulation installed with a white reflective sheeting over the insulation. robo hippy

[Clint]

Around here (central Alberta, Canada), the 24" insulation is about as common as the 16". Don't know about other places, though. Even though the 16" wide insulation is less per square foot, I went with the 24" wide for the ceiling, as I was putting up vapor barrier at the same time, and I didn't figure the two pieces would stay up there long enough for me to tack up the plastic. In your case, with a finished floor, I don't think it would really matter, but I'd look at renting an insulation blower, and buying the loose fill stuff.

[marks542004]

Check the building codes for your area. The 24" is generally not available if the local code does not allow 24" framing.

The joints are not a problem if you can keep the bats firmly pressed against each other.

I would consider throwing a piece of something like tyvek over it to keep dust out of the insulation and to provide another air barrier.

[TP]

++++++++++++

Interesting I guess I never thought of laying tyvek over the top of the pink stuff. Seems like it could trap moisture? Does dust hurt the insulation? Why doesn?t any of the insulation manufactures suggest doing this? I have a half a roll of Lowes house barrier leftover, maybe I?ll unroll it in my attic?

TP

[Chris Lewis]

According to flipper :

If you're doing unfaced batts, the seams are irrelevant if you've installed it properly.

R13 is for 2x4 stud walls, and R20 is for 2x6 walls. Building codes generally do not permit the use of 2x4s on 24" centers, hence, 24" R13 is a pretty rare size.

You need to base your insulation selection on desired R-value, not batt width. With unfaced batts, the determining factor in cost per square foot is R value (thickness) not batt width.

There's probably a reason that insulation manufacturers don't suggest using building wrap on top of ceiling insulation - it's a bad idea. Dust in the insulation will not make much of a difference, and you want to minimize as much as possible any blockage of moisture transfer _out_ of the insulation.