Wall Insulation and vapor barrier

[Stuart Brooks]

I had a pre-drywall inspection today. The builder had already installed wall insulation. I notice that they had the vapor barrier reversed in 3 locations: 1) garage wall where a HVAC chase is located, houses duct work and B-vent for furnace; 2 & 3) Exterior wall beside bathtubs. They were using Kraft paper backed fiberglass batts for insulation. Since I don't usually see insulation, shouldn't there be a plastic barrier on the inside of the insulation at the bathtubs? The builder is going to use the new mold/moisture resistant drywall around the tub (no cement backer board).

[Scott Patterson]

I had a pre-drywall inspection today. The builder had already installed wall insulation. I notice that they had the vapor barrier reversed in 3 locations: 1) garage wall where a HVAC chase is located, houses duct work and B-vent for furnace; 2 & 3) Exterior wall beside bathtubs. They were using Kraft paper backed fiberglass batts for insulation. Since I don't usually see insulation, shouldn't there be a plastic barrier on the inside of the insulation at the bathtubs? The builder is going to use the new mold/moisture resistant drywall around the tub (no cement backer board).

OK, I'm a little confused... Yes, I know that is not unusual! :)

The Kraft paper needs to face the the warm or conditioned side of the home. It even has a small edge that can be stapled to the studs.

I don't understand the HVAC chase, does it have ductwork and the furnace B vent in the same chase? What kind of ductwork?

The reversed insulation at the tubs makes no sense. NO, you do not want to add plastic sheeting. If you did this you would have a mess.

The builder needs to use drywall or backer board that is approved for wet/damp locations.

[Jerry Peck]

I notice that they had the vapor barrier reversed in 3 locations: 1) garage wall where a HVAC chase is located, houses duct work and B-vent for furnace; 2 & 3) Exterior wall beside bathtubs.

4) in the ceiling above the garage

Presuming the first photo is the garage and is showing the 3 stud bays with reversed insulation, to the right 2 stud bays and up in the ceiling - looks like more reversed? If not, what is that?


The builder is going to use the new mold/moisture resistant drywall around the tub (no cement backer board).

Make sure it is rated by the manufacturer for that installation, much of it is not approved for installation in those "wet areas" around tubs or showers.


The builder needs to use drywall or backer board that is approved for wet/damp locations.

Precisely, and you need to check with the manufacturer's web site and get their information if you do not already have it - much of the new stuff is STILL NOT approved for those wet areas.

[Jerry Peck]

At the B vent in the wall, they should use batts without the backing. If the heat causes sweating, where will the moisture stop? Inside the wall. :mad:

The paper is not a "barrier" it is a "vapor retarder". That should not cause any problems (with the insulation facing in the correct way).


At the tub, they should have the vapor barrier on the interior side. In my area, we would be using poly on all the interior walls. Call it out, it is an easy fix now, it will cost them 1/2 a bundle of insulation to put it right. You have the pics to prove they screwed up.


Maybe up there, but anywhere I know of putting in a plastic sheeting behind the tub and tile surround WILL CAUSE problems.

[John Kogel]

The paper is not a "barrier" it is a "vapor retarder". That should not cause any problems (with the insulation facing in the correct way).




Maybe up there, but anywhere I know of putting in a plastic sheeting behind the tub and tile surround WILL CAUSE problems.Acknowledged. Different climate. I've deleted my post to prevent confusion. However, isn't there a concern with the paper in proximity to the B vent, therefore they turned the batts around?

[Jerry Peck]

However, isn't there a concern with the paper in proximity to the B vent, therefore they turned the batts around?


Not as long as required clearances are maintained.

[Stuart Brooks]

Garage insulation (1st picture, paper towards garage) - HVAC chase: Metal duct, uninsulated, Main supply duct and return duct for 2nd floor registers; Return duct is against the insulation in between stud area; B-vent is more than 6" away from insulation and between the two metal ducts

Bathroom: the drywall in the tub/surround area, maybe whole bathroom, is the new material with GP DensArmor Plus. The fiberglass faced gypsum drywall material that can be used where "green board" is usually required.

I agree that properly installed cement backer board is the best product to use around tub/shower enclosures but isn't that a matter of builder's choice? We're talking about a National Builder where lowest cost per unit is the driving force.

[Jerry Peck]

The fiberglass faced gypsum drywall material that can be used where "green board" is usually required.

You mean ... where "green board" (MR board) *was used*, but not really allowed, and certainly not required. Some manufacturers realized that MR board was not allowed before other manufacturers did, and not they all say it is not allowed for that use.

I agree that properly installed cement backer board is the best product to use around tub/shower enclosures but isn't that a matter of builder's choice?[/quote]

"isn't that a matter of builder's choice?"

Not if you are comparing it to something *which should not be used* around tubs and shower areas.

[Markus Keller]

Unless that tub is an outside wall, which it looks like it is; I recommend people not put insulation in the cavities around the tub. If there's a leak, the itch just soaks it up and it takes a lot longer to show.
As far as backer board ... I've seen the DensArmor used in tubs. I don't like it any better than greenboard. Haven't looked it up to see it's Spec's. Check out Densshield though, kickass tile backer, works well, holds up, never had a single call back, nice product to work with, glue and mortar sticks well.

[Jerry Peck]

Bathroom: the drywall in the tub/surround area, maybe whole bathroom, is the new material with GP DensArmor Plus.



As far as backer board ... I've seen the DensArmor used in tubs. I don't like it any better than greenboard. Haven't looked it up to see it's Spec's.

Nothing in the DensArmor Plus materials (specs / submittals / installation / etc.) says anything about it being acceptable for use around tubs or showers - so that would be a big no-no.

*IN* "bathrooms", yes, in areas *other than* around tubs and showers.

If you are seeing DensArmor *IN* the tub surround and shower wall (and ceilings over tubs and showers) then it is wrong.


Check out Densshield though, kickass tile backer, works well, holds up, never had a single call back, nice product to work with, glue and mortar sticks well.

DensShield *IS* a tile backer board and the information for DensShield *DOES* specifically state it is for those areas:
http://gp.com/build/documentviewer.aspx?repository=BP&elementid=6875
http://gp.com/build/DocumentViewer.aspx?repository=BP&elementid=3112