advice needed about insulation under sheetrock

[rockchuk1]

Hello again, gang...it's been awhile.....say, I need some advice please.  I've been remodeling and turned a pretty blah bed room into one with vaulted ceiling that's going to be pretty cool when it's done (fingers crossed).

I am reusing the old fiberglass insulation that was in there originally.  However, when I pulled it out the vapor barrier came off of it (on some of it was aluminum, and some had an asphalt backed kraft paper).   The batting is fine though.

So I have all the fiberglass batting back in and am ready to sheetrock, but I need to know if I need some kind of vapor barrier between the insulation and the sheetrock?

A few considerations:

*** The outside wall has heavy 30 lb felt under the siding....an apparently good barrier as there was little wood rot found anywhere.

*** The roof does not leak.

*** Since I have now vaulted the ceiling, the rafters are now of course also the ceiling joists....unfortunately the rafters are only 2x6's, so the fiberglass is 4" in order to leave some kind of a ventilation space.

*** We live in the northwest where there is plenty of humidity.

I'm thinking that putting a vapor barrier between insulation and sheetrock is bad news due to condensation....but wasn't sure.  Can I just go ahead and sheetrock it as is?

As always, thank you very much for your good and kind help!
Rockchuk

[rwalter]

rockchuk1,

Install the fiberglass batts and then staple to the studs at least 3mil polyethylene plastic sheeting. Out in the Pacific Northwest from what I hear they have a lot of problems with moisture entering so you might want to use 6 mil plastic. You can buy the sheeting at most lumber yards or at any Home Depot or Loews. That is the standard technique used when installing unfaced insulation.

[John Raabe]

What rwalter suggests is what we did in 1983 when I built my house on Whidbey Island (Puget Sound, WA).

I have had no regrets and no moisture problems. The house has been quite energy efficient and has low heating bills and no drafts.

There has been an ongoing debate about such moisture barriers for over 30 years. In cooling climates they probably don't make sense, but in cold winter locations, especially in windy areas, I think they are worth the time and expense and help the house last longer.

[rockchuk1]

Hi John and rwalter....thank you both for your thoughtful replies....however, now I'm even a bit more confused, so please bear with me.  I talked to an older guy who works at the lumberyard about this yesterday....he said that they did what you're suggesting in a house in eastern Oregon, and it basically rotted from the inside out.

Why would something like that happen?  It's much colder in eastern OR than it is here on the coast, but it's much drier than here too.  So, you don't think this would cause a condensation problem here then?  John, you being on the Puget Sound should know first hand about this stuff, so I'm all ears.

Man, like you say, it's really hard to get a definitive answer on this....yesterday 3 guys all gave me different answers, and now you both are saying to use the plastic.  One guy suggested I use something called "Aquabar Kraft 30-30-30 paper".  It's impervious for the most part, but heck, if impervious is the way to go, then I'd rather put in the heavy plastic like you suggest....I just still wonder about any potential condensation problems.

Then another older guy with some experience said not to put anything in, just sheetrock over the batting.  Sigh.....

Thanks again, John and rwalter.....I had no idea this would have been such a toughie to pin down.  More thoughts please!!!!  
rockchuk

[rockchuk1]

A postscript......we plan on working down south in the winter for 2-4 months every winter, so the house would be empty with little heat during that time....is this a consideration as well?

[PEG688]

roc  My to bits , yes Glenn , we know .   Is this , sounds like a older building that as you said had very little,, no rot . With the same insulation your reinstalling , yes with out the paper / facing .   The old foil faced stuff , I think was just a way to hold the insulation so you could install it .  

  I'd go with out the plastic , I do wonder how you'll hold that insulation up , so it won't slide down the stud bay , in  normal use / compress.

  We use a PVA primer that is also a vapor barrier on the drywall it self.

  You'll leave a little heat on when your gone , like 55 or so ?  

   I think it will be fine without , but see settling problems. and cold spots at the top .  

 HTBH  ;)PEG