Bathroom greenboard/vapor barrier/insulation

Hello all, coming up on the sheetrock stage on my master bath addition and had a few questions. I have exhausted myself trying to find the answer to my somewhat unique problem. My master bath is on the second floor of my house, and the second floor outside walls consist of knee walls floor to ceiling. The stand up shower and whirlpool tub will both be on the out side walls against the knee walls.

First, I have read that you NEVER use a vapor barrier behind greenboard. Do I just insulate the wall with unfaced insulation, and use insulation hangers to hold the insulation into the stud bays? I have little to no access to the back side of the knee wall. The knee wall is about 2 feet at the floor and evens out with the 8'ish ceiling on top.

The idea of not using a vapor barrier to block the cold here in new england really bothers me. The 1/2" greenboard will block some of the cold, but without some sort of vapor barrier im worried that my shower will be a cold one for the winter.

 

There is no real reason to use greenboard anymore. If you tile, you use concrete backer underlayment, not greenboard. If you don't tile, you install vapor barrier, sheetrock, prime and apply a good paint.

 

I've never heard "never use a vapor barrier behind greenboard". But doesn't matter because I don't use the stuff. Go with the vapor barrier. Don't use green board. Like Chandler says use some sort of tile backer behind tile. If not then just use regular rock and a really good paint.

 

Hi Dynamci, I'll take on the insulation issue. A knee wall is generally a vertical wall less than full height between the living space and a side attic. It sounds like you are including the sloped ceiling in that description, or I'm lost, which is common.

Anyway, the 2' vertical section where you can't get to the back of it, needs some detail work. I'll wait for answers before going into details.
1. Is that side attic space open to the eaves for venting?
2. 2x4" or 2x6" knee wall?
3. If a slope, is it vented all the wat to the attic and what are the rafters, 2x6"?
4. What do you have for insulation in rafters?
5. What do you have for air blocks and insulation in floors?
6. What do you have for an exhaust fan and where is it vented to?

That will get us started.
And I agree with advice above.

Bud

 

1. Open to eaves for venting! yes
2. 2x4 knee wall floor to 8'ish ceiling
3. slope, yes, but the slope is only on the roof pitch, bathroom is squared. bare walls at the moment, 1940's dimensional 2x4's framing outside walls and slope, rafters are also 1940's 2x4's.
4. nothing at the moment.
5. nothing at the moment.
6. exhaust fan on list of things to do and will be vented outside of house(back wall).

 

SO,

use regular 5/8" sheetrock on all walls.

Insulate and vapor barrier as normal.

primer and paint with good primer, and "bathroom" paint.

Install appropriate sized ceiling fan.

GI2

 

1/2" sheetrock is fine. 5/8" is heavy. Right on the primer and paint. And you mean "exhaust" fan, not ceiling fan, I am sure. Check the volume and the Sones of the fan you choose and try to get both eggs in the same basket.

 

Sorry, I missed your reply. I hope the walls are still open, lots of important details that can be taken care of. Here is a detailed link for air sealing, the number one energy improvement you can make, at least easily.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud

 

.actually, I meant "FART" fan...

Im still kind of fond of the 5/8" for a sound barrier, durability, fire protection and such.

great pdf!! lots of great info. Beer 4U2

 

"Im still kind of fond of the 5/8" for a sound barrier, durability, fire protection and such."

To each his own, but in a bathroom with all the water, fire is the last thing that crosses my mind. Sound proofing can be achieved via better insulation.