Tuff-R instead of fiberglass......

[charry]

Looking at replacing the insulation in the walls of a small office. I pulled down the (wrecked by glued panelling) drywall, to reveal some

*very* old fiberglass insulation (which is now about 1" thick).

Question is, should I just replace with R13 batts, or can I put rigid foam (like Tuff-R) in its place. I know the Tuff-R gives a better R-rating, so should I fill the cavity completely? (2x4, so 3 layers of

1" Tuff-R), or just do 2 layers and leave the rest open?

Also, if I use the Tuff-R, do I need to put up a plastic vapor barrier before putting the drywall back on? Or would the foil facing serve as a vapor barrier?

Thanks in advance!

-Chris

[marson]

you could use Tuff-R, but it would be labor intensive to install between studs. also, it would be very difficult to fit around all the obstacles one encounters, like wires, pipes, etc. it also would be hard to get a good fit to the studs (though you could fill any gaps with spray foam. if you really want a good job, use fiberglass, and then cover the wall with tuff r. tape the seams with red tyveck tape for your vapor barrier (caulk to floor, etc.)

[charry]

I thought about that too, seems like a good enough idea but I wouldnt know how to get all of the receptacles (easy enough to fix I guess) and window frames (not so easy to fix) to match up to the wall being an extra 1/2" thick.

Maybe Im just better off with Kraft faced R13.

-Chris

[marson]

yeah, that's true. boxes can be moved or extended, and window jambs can be extended (often lumberyards will sell a stock molding called parting stop that measures 1/2" by 3/4" which can be used to extend the jambs), but that amounts to work too. if you work with a building inspector, he'll doubtlessly have an opinion.

[charry]

I dont mind the extra work, just wondering if the extra insulation value is *worth* the extra work.

R13 with the vapor barrier already attached seems a lot easier, but I dont know if Ill kick myself for not having the Tuff-R over it, figuring Id get another R3 or R4 depending on the thickness.

-Chris

[marson]

well if you don't mind the extra work and expense, go for it. i think you get a better air barrier using tuff r versus poly, and you minimize thermal bridging (whereby heat is conducted through the studs themselves).

[charry]

One final question - anything wrong with having *2* vapor barriers?

Just got back from HD, and all they have for 2x4 walls was Kraft-faced batts. Can I put those up and then the foam over it? OC makes an R-15

2x4 batt now, so at least I got a little more than R13. Id like to use the foam if I can, but not if its bad to have dual vapor barriers (assuming the Tuff-R acts as a vapor barrier)

Thanks!

-Chris

[marson]

two vapor barriers is fine. in fact, if you wind up using the kraft faced with no foam, then add a 6 mil poly vapor barrier. the kraft paper is really not considered an adequate air barrier any more (at least here in MN!).

[charry]

Thanks! Didnt know that about the Kraft paper.

But at this point it seems easier to put 1/2" foam on instead of a 6 mil vapor barrier. Less work, looks better (behind the drywall ;) ) and will insulate that much more.

Thanks for the advice!

-Chris

[charry]

Oh yeah forgot to ask.....

How sould I fasten the foam in place? Can I just glu eit to the studs?

-Chris

[marson]

i would just get "plasticap nails" which they should have at HD. they are a nail with a plastic washer head. roofing nails would probably work too. whatever you use is temporary until the drywall goes up anyway. remember when you put your trim etc back up that you have to allow for the extra 1/2 of foam so you might need a longer nail glue is fine, but that seems messy and like more work.

[jgb]

If you want to maximize the R-value of the R13 (or any insulation for that matter) then you should use expanding foam to seal any penetrations through the exterior wall and/or each cavity. This will create dead air space in each cavity and allows the insulation to be most effective. You can use the low expansion stuff. Check the price of the R15 vs the R13. R15 tends to be very pricey and if you're going to use Tuff R then I don't think you'll need it. You can simply increase the thickness of the product. I just would go any thicker than 1.5" because then you'll have a hard time keeping the drywall flat. Any way to attach the foam to the stud temporarily will be fine since it will be screwed tight once you apply the drywall over it will also fasten the foam. You could probably nail it but make sure the nail head doesn't stick out since it will also interfere with the drywall.

Good luck.