Insulation Question

[Mike Wilkins]

I am planning to close in my shop ceiling joists and could use a suggestion for insulation. They are 2 X 6 joists, 24" OC. I know fiberglass batts are available, but I am also considering rigid foam. These come in 4 X 8 sheets from the local Lowes. I could cut to fit between the joists, using 1.5 or 2 inch thick sheets. Anyone see a reason not to use the foam??? Thanks for the collective wisdom.

 

[SawBuck]

Hi Mike,

I originally considered closing in my shop's ceiling with the rigid foam sheets too. After pricing out the materials I found that sheeting the ceiling with OSB was by far the cheapest, and it gave me a good substrate to fasten light fixtures and DC duct work to. I also thought I could insulate the attic space myself with fiberglass batts and save a bunch of money. It turned out that I could hire a local insulation co. to blow in a higher R value blanket than I could buy myself, and the labor was included. My only regret was not taking the extra time to paint the OSB white first.

-Lonnie

 

[Skymaster]

If you use any kind of open heat source, foam NOT a good idea. otherwise it is ok. just put 1 x 2 ledger all the way around bottom edge of joist to rest foam on. Also if you have lights in/on ceiling be very careful with closeness of foam to fixture

 

[Bill Clemmons]

Like Lonnie, I found the cheapest / best solution was to have insulation blown in by a professional. Install your ceiling, get your wiring in order, then have it done. One caveat: if you have any can lights, make sure they are rated "IC" to come in contact w/ insulation.

Bill

 

[SteveHall]

Rigid foam is more flammable than glass fiber. (Isocyanurate has better resistance and lower flame spread than polyurethane; alternatively, glass fiber backing is somewhat combustable.) It also melts when heated and can drip during a fire (only a problem on commercial roof decking or within tall building walls). Usually it is also a little more expensive.

The pluses are that it is better R per inch thickness when properly joined and taped, it provides the same insulation value when wet, and it provides less of a burrowing opportunity for rodents.

Glass fiber is going to be more convenient between wooden construction members (properly sized) and will have a snugger fit, and therefore actually perform better than loose-fitting rigid. Unless you can get rigid at a great price, I'd go with the batten.

 

[Phil S]

I am also getting ready to insulate my shop ceiling. Foam from the big boxes runs about $25 to $30 per sheet for 2" r10 Approx a buck a foot - that seems pretty high. You can buy r30 for only 31cents per foot. If you buy the big rolls at either the blue or orange stores they cost almost 81 cents/sqft but if you get the small 15" x 25' roll from HD for $9.95 it is a good deal - please leave enough for me

 

[junquecol]

I like to insulate between joist with fiberglass, add a layer of 3/4 foam on bottom, and then cover with 5/8" sheetrock. After taping joints, paint ceiling with ceiling white paint. Foam prevents "thermal bridging" of joists. You do have to use 2 1/2" screws for the sheet rock.

 

[ScottM]

When I built last year I used 6" fiberglass between the 2X4s. My ceiling is OBS which I painted white.

 

[Skymaster]

Scott; hmmmmmmmmmmmmmmmmmmmm new material eh? OBS? not OSB?
:rotflm::rotflm::rotflm::rotflm::rotflm:


sorry da Devil made me do it

 

[ScottM]

Scott; hmmmmmmmmmmmmmmmmmmmm new material eh? OBS? not OSB?
:rotflm::rotflm::rotflm::rotflm::rotflm:


sorry da Devil made me do it

:tinysmile_cry_t::BangHead::BangHead::BangHead::embarrassed::embarrassed::embarrassed:

 

[Skymaster]

Please dont b :gar-La; I just couldnt resist 'cause I am just a mean,old,Da** Yankee carpetbagger
:rotflm:

 

[golfdad]

We use the Ridgid insulation a lot on the job....its hard to cut and fit tight...I put 2" in my shop but screwed it directly to bottom of the joist's....Chk with some big construction Co's they might have some leftover cheap