Insulation, Radiant and Vapor Barriers - vapor barrier on bathroom ceiling

Good day ladies and gentlemen
I am presently fixing the ceiling on a residential second floor bathroom on a house built in 1978. The home was constructed with poly vapor barriers behind the drywall on exterior walls and behind the drywall on ceilings NOT abutting an attic space. Ceilings next to an attic space have no vapor barrier - with insulation consisting of blown cellulose and unfaced rolled fiberglass on top.
The current bathroom ceiling has some water damage due to an exhaust fan that was not vented to the outside. The fan is now vented outside and I need to know how best to repair the ceiling. Specifically, should I:

1) add a layer of 4 mil poly on the bathroom side of the existing ceiling and then fit a new layer of 3/8" non MR drywall on the bathroom side of the poly?

2) Not add the poly, but fit a layer of 1/2" greenboard to the ceiling?

3) Fix the existing drywall by replacing the bad section and continue without a vapor barrier?

The bathroom does have a skylight with a drywalled shaft between ceiling and glass. Also, cursory inspection was unable to detect any mold or rot in drywall except for the are near the crappily installed fan.

Thanks in advance for your advice. I greatly appreciate the feedback. The research I have done independantly on the web was contradictory and confusing.

-ryan

Ryan: Don't do #1. You will create a water sandwich that way. I would go up into the attic, remove the insulation from the ceiling area, and either reinstall faced insulation (face down) thereby giving you a vapor barrier. Once you solved the problem with the fan I think you may have it licked. They are the most offending parts of the bathroom (skylights do it too). Then, you could either repair the damaged area, or resurface the entire ceiling with 3/8 or 1/2 sheetrock, finish, prime and paint or knockdown. Whatever you do, don't use popcorn in a bathroom!! I've got it in my bathroom and would like to place my hands gently around the contractor's neck.

A bathroom produces a tremendous amount of moisture. If this moisture enters your attic space it could lead to some severe problems, i.e. rot, mold, frost etc. I cannot understand why there is a VB in other parts but not above the bathroom.

My recommendation would be to apply the poly and then greenboard over top of that. The poly will prevent moisture from entering your attic and the greenbaord is moisture resistant and necessary in a bathroom.

I do appreciate the feedback, but sadly it looks as if there remains disagreement as to how best to proceed. I would question how a water sandwich is being created in scheme number 1, as the only material with any vapor retarding properties is the poly sheet - the standard drywall and unfaced insulation allow a path to atmosphere on either side of the sheet. Also, other threads on this website warn against placing greenboard on the ceiling of a bathroom. I was told it not only is inadvisable, but non-code compliant. Maybe some further discussion can help flush out the issue.

Ryan: Don't do #1. You will create a water sandwich that way. I would go up into the attic, remove the insulation from the ceiling area, and either reinstall faced insulation (face down) thereby giving you a vapor barrier. Once you solved the problem with the fan I think you may have it licked. They are the most offending parts of the bathroom (skylights do it too). Then, you could either repair the damaged area, or resurface the entire ceiling with 3/8 or 1/2 sheetrock, finish, prime and paint or knockdown. Whatever you do, don't use popcorn in a bathroom!! I've got it in my bathroom and would like to place my hands gently around the contractor's neck.

Why not use popcorn? We have it in every room of our house. I see on tv that a lot of people are scraping that off. What gives?

I am not a fan of the popcorn texture look, but that is just my personal aesthetic preferance. I was able to find some excellent information from Building Science Corp entitled "Vapor Barriers and Wall Design". I have a pdf of the report and can email a copy if anyone is interested. They subjected several wall assemblies to computational heat flow analysis. By then cross referencing temperature with a psychometric (sp?) chart, they were able to determine whether the dew point would be reached within the wall cavity. This was done in several climactic zones of varying heating degree days and relative humidity. Taking some measurements of my ceiling assembly and using there data, I decided to retrofit craft faced insulation and maintain an R value of at least 38. This has the added advantage of being re-configurable in the future without major demo work.

About four years ago I teamed up with a company that specializes in mold remediation. We did a bathroom remodel in a youth group home which experiences a great deal of use 24/7. The humidity levels were very high and some areas of the drywall had black mold. We also found wet black mold on the warm side of the vapour barrier which demonstrated that the barrier was working and that the moisture was internally generated. The old fiberglass insulation was also dry.

This work included complete replacement of the drywall and a shower enclosure (with aqua board behind). The noisy ceiling fan was replaced with a self regulating Passivent which opens and closes automatically (without electricity). It operates automatically whenever the humidity levels are too high then closes automatically when the humidity is at acceptable levels. The walls and ceilings were coated with a multiceramic insulation coating which actually prevents condensation from develloping. The reflective ceramics prevents the warm air molecules from touching the coated surfaces thus preventing dew point. To this day not a drop of water has develloped on the walls and ceilings even after a shower or bath. The electric baseboard heater is kept at a lower than normal temperature during the winter months since we used this coating as it is so effective in preventing heat from transfering through the walls and ceiling. The end result shows this system works well. The utility consumtion has been reduced significantly and the humidity levels remain low.