Adding insulation to attic – mix and mat
sweetlake
| Posted in Energy, Heating & Insulation on
I’ve got an attic with FG batts in various thicknesses around trusses (from 3.5 to 8 inches). The fixtures are very leaky and the FG isn’t even around the trusses. Reading the multitudes of threads leads me to believe Cellulose is the best insulation but I’m not sure about blowing it on top of the FG. I’d like to fill all those gaps around the trusses. I also read about weight issues (24″ spanned with drywall that has already sagged a bit). Is this a problem?
As far as air sealing around ceiling fixture boxes in the attic- can I tape off the holes and then seal with foam? Is there a best practice?
Thanks for your help. Ted
Edited 1/25/2006 1:44 am ET by sweetlake
Edited 1/25/2006 1:46 am ET by sweetlake
Replies
just blow about two feet of cell on top of the bats. The weight is not an issue, Cell will glue itself together and almost self supporting
any ideas on sealing electrical boxes? I'm considering using foil tape to block the little holes/gaps and 'great stuff'ing around them.
I've used a soundproofing product on electrical boxes. It's basically clay in sheet form, maybe 1/8" X 8" x 10" or so. It's designed to seal the holes where wires penetrate, and deaden the box, but it's fireproof and heatproof and would work fine for sealing boxes for insulating purposes. I bought a box of it for a job a few years ago... now maybe I'll be able to remember what it's called.
As for sealing the boxes I have made a 8x8x4 box out of 2" foam glued together with my foam gun and then glued to the ceiling rock with the same foam gun.just make small notches were the BX or Romex come out and your off to the races.I made the boxes in the comfort of my garage. brought them all up at the same time and had them in about as fast as I could move around the attic. Surely beats plugging a boat-load of seperate holes on you knees in an attic.I agree about the insulation on top of the FG--shouldn't be a problem.Mike" I reject your reality and substitute my own"
Adam Savage---Mythbusters
I'm finally getting to the point of blowing insulation in the attic I originally posted about. About half of the attic has 12-15 inches of FG with gaps where the trusses are (see the picture) The other half is only about 4-6 inches deep. How much cellulose do I need over the FG in the thick areas to halt the airflow? The other thing is I'd like to have a walkway down the middle of the attic to access some storage shelves. I had a couple of pieces 2 inch foam and some plywood, (see the picture) Would this make an acceptable comprimise (energywise)? Once the cellulose is blown how do I access the place with out squishing the insulation?
Forgot the pictures - oops
Our insulator will blow in cellulose over fiberglass, and it makes for a nice job, in my opinion. They have to baffle around things like woodstove vent pipe and some types of recessed lights, but otherwise you get very uniform coverage.
An alternative would be to lay more FG across the top of the existing.