Doubling Up On 2in Rigid Fiberglass

[c7sus]

I'm having one helluva time here finding 3 and 4 in unfaced rigid fiberglass.

I called O/C a couple weeks ago, and they called back telling me to call a local wholesale house. Called them, they say they have it.

Call today to check availability, they say no, and the MINIMUM order is 3000 square feet of each! That's about $12,000 of the stuff!

My local guy has 1 and 2 inch in mass quantities. If I stack 1"& 2" to make 3", and 2" & 2" to make 4in worth of treatment, do I get similar IRC ratings for the effort???

I can get as much 3inch Rockwool as I can use, but the weight difference is 5 lbs/cubic foot. The difference works out to 32lbs and 43 lbs for my application. That's a significant difference to me!

Thanks!

[scottboyher]

Yep.. I am totally confused now..

[c7sus]

I just got a call back from a guy named Bob Gardner at Knauf Corporate. He's their technical guru on this stuff.

He said stacking the material was acceptable, even though if you look at the IRC ratings between the different thicknesses it would seem to defy logic.

He also recommended staggering the joints when used this way.

Now for the price difference between using mineral Rockwool and Knauf:

About DOUBLE to use Knauf over Rockwool!

[sheppard]

Graig,if you are having trouble locating 4"rockwool,try contacting
your local Hilti products dealer.They carry a lot of fire proofing
products and can most likely put you on to a dealer that has
what you need.(especially if they somehow got the impression
that you were a contractor that might possibly purchase some of
their highly expensive fire proof caulk.$400 for a 5 gal. bucket)
might be worth a try.

[c7sus]

I think at this point I'm gonna go with 3in Rockwool for the absorbers and double up the 2in Knauf in the slot resonator.

The price difference is about $125US!!!!

I was trying to keep these monsters below 100 pounds/panel but I can see now that's just not gonna happen..............

[Michael Jones]

Originally posted by c7sus
...I was trying to keep these monsters below 100 pounds/panel but I can see now that's just not gonna happen..............

Cut 'em in half!