Type of insulation behind greenboard


Old 02-11-09, 03:05 AM
Thread Starter
Join Date: Sep 2008
Location: Ca.
Posts: 84
Type of insulation behind greenboard

I am installing greenboard on a bathroom wall which is the inside of an exterior wall. So would like to insulate wall. Is there any problem with installing faced insulation? Does green board act as a vapor barrier and would I be trapping moisture between the two? I believe the perms rating on greenboard is around 30 ( Could not confirm spec) which if I understand the theroy correctly means its not a vapor barrier. The permeability rating states if less then 1.0 it's a vapor barrier.So, with a perm rating of 30 does this mean it's OK to put greenboard over the faced insulation? My understanding is greenboard is just drywall with special paper to not promote mold. Any help appreciated.
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Old 02-11-09, 03:25 AM
Join Date: Feb 2006
Location: New York
Posts: 174
Greenboard also has a diiferent core. You don't say whether if you are tiling this wall or not. If you are, there are much better materials to use than green sheetrock. We have been using Denshield or Durock depending on the job. For insulation, I would use conventional fiberglass sized for the wall framing. You're probably going to get a lot of other opinions here.
Old 02-12-09, 07:33 AM
Join Date: Dec 2003
Location: USA
Posts: 994
From what I've read, green board is actually worse than regular drywall in a moist environment. It is no longer legal to use in some locations.
Old 02-17-09, 06:06 PM
Join Date: Nov 2007
Posts: 39
Green board is made with a water-resistant formula to prevent moisture trapping and resultant mold, deterioration, weakness of substrate, and so on.

Different manufacturers use different formulas so to be sure about the one you plan to use, check the manufacturer's website and get the detailed specs. If the green board is going behind a FG tub or shower unit, most mfrs. recommend priming it with a good grade of paint to inhibit moisture penetration If you are backing up tile around a tub or shower go with Durock or some other cement board in spite of the extra cost. Green board is more than satisfactory as a tile backer in open walls and celilings with thinset mortar.

Using FG with a vapor barrier on one side is the recommended way to go to allow moisture in an exterior wall to migrate outward. Remember that the vapor barrier is always placed against the inside wall surface regardless of what it is.

ext wall surface< fiberglass insul< vapor barrier< inside wall

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