# vapour barrier on ceiling of bathroom?



## wilsonfrench (Dec 26, 2008)

Hi. my contractor has just finished our bathroom. He did not put a vapour barrier on the ceiling ovver the shower....he did use (however) blue board. He tiled over this blue board....
in the attic is blown insulation. 
My question: did this ceiling need to have a vapour barrier? if so, now what? I cannot take down the tiles and add a vapour barrier...can I install a vapour barrier from the attic?
or will it be ok without a vapour barrier?
I was told that moisture will go up into attic and the air will be let out by the vents and the air coming in through the soffits...
any help? suggestions? thoughts? thanks


----------



## Just Bill (Dec 21, 2008)

Technically there should be a vapor barrier, but many things qualify as a vapor barrier, including paint. The vapor barrier is usually installed on top of the ceiling under the insulation. Tile would certainly qualify as a vapor barrier. But a drywall or plaster ceiling sealed with a primer and top paint coat also qualifies, most of the time.


----------



## bjbatlanta (Jul 16, 2008)

I've never seen any sort of specific vapor barrier used on ceilings (such as plastic). Make sure you have an adequate exhaust fan vented to the outside of the house, and as Just Bill stated, proper paint on the exposed drywall.......


----------



## AtlanticWBConst. (May 12, 2006)

wilsonfrench said:


> Hi. my contractor has just finished our bathroom. He did not put a vapour barrier on the ceiling ovver the shower....he did use (however) blue board. He tiled over this blue board....
> in the attic is blown insulation.
> My question: did this ceiling need to have a vapour barrier? if so, now what? I cannot take down the tiles and add a vapour barrier...can I install a vapour barrier from the attic?
> or will it be ok without a vapour barrier?
> ...


The point of applying a vapor barrier onto insulation (facing the warm area) is about condensation/humidity from temperature change (cold air meeting warm condiitoned air). In the situation/arrangment that you describe, there should be some sort of vapor barrier between the insulation and the warm area (bathroom). Dependent on regional building codes, this may be required because of the cold air meeting warm (heated) air (aka = dewpoint condensation). 

As far as vapor coming thru the ceiling's painted drywall surface, this just isn't going to happen. If you have an exhaust vent, properly installed, and venting the moist bathroom air to the outside, and a proper coat of mildew resistant paint, these should suffice to protect the drywall from any moisture. 

Now the thing I find hard to understand is, if the guy installed the blueboard and you have blown-in (loose) insulation, how did that stay up, when there was no sheetrock on the ceiling? 

As far as mositure in the attic, you don't want that. But this is not going to take place from vapor traveling thru painted (protected) sheetrock. If you have an exhaust vent, make sure that is vented to the outside, and not into your attic.


----------



## AtlanticWBConst. (May 12, 2006)

Just Bill said:


> Technically there should be a vapor barrier, but many things qualify as a vapor barrier, including paint. The vapor barrier is usually installed on top of the ceiling under the insulation. Tile would certainly qualify as a vapor barrier. But a drywall or plaster ceiling sealed with a primer and top paint coat also qualifies, most of the time.


Just to Clarify:

Tile in and of itself is not considered a vapor barrier, neither does a top coat of paint over drywall.

Are these areas able to resist moisture vapor? Yes, to a degree.

Are such surfaces categorized by building code, or industry standards as proper/recognized "vapor barriers" or "vapor retarders"? No, they are not.

http://en.wikipedia.org/wiki/Vapor_barrier


----------



## AtlanticWBConst. (May 12, 2006)

More information on vapor barriers and regional needs: http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11810


----------



## wilsonfrench (Dec 26, 2008)

*venting an exhasut fan through soffit hole*



AtlanticWBConst. said:


> The point of applying a vapor barrier onto insulation (facing the warm area) is about condensation/humidity from temperature change (cold air meeting warm condiitoned air). In the situation/arrangment that you describe, there should be some sort of vapor barrier between the insulation and the warm area (bathroom). Dependent on regional building codes, this may be required because of the cold air meeting warm (heated) air (aka = dewpoint condensation).
> 
> As far as vapor coming thru the ceiling's painted drywall surface, this just isn't going to happen. If you have an exhaust vent, properly installed, and venting the moist bathroom air to the outside, and a proper coat of mildew resistant paint, these should suffice to protect the drywall from any moisture.
> 
> ...


 
Hi. I have installed the exhaust fan with a hose that expells the warm air through the a hole (which I cut) in the soffit....will this warm air be sucked back into the attic? ..thereby defeating the whole purpose of an exhaust fan? 
I Have peforated soffits..thanks


----------



## wilsonfrench (Dec 26, 2008)

Just Bill said:


> Technically there should be a vapor barrier, but many things qualify as a vapor barrier, including paint. The vapor barrier is usually installed on top of the ceiling under the insulation. Tile would certainly qualify as a vapor barrier. But a drywall or plaster ceiling sealed with a primer and top paint coat also qualifies, most of the time.


...

not sure I understand...can I retro-install a VB now? in between the joist bays ?


----------



## wilsonfrench (Dec 26, 2008)

*venting an exhasut fan*



wilsonfrench said:


> Hi. my contractor has just finished our bathroom. He did not put a vapour barrier on the ceiling ovver the shower....he did use (however) blue board. He tiled over this blue board....
> in the attic is blown insulation.
> My question: did this ceiling need to have a vapour barrier? if so, now what? I cannot take down the tiles and add a vapour barrier...can I install a vapour barrier from the attic?
> or will it be ok without a vapour barrier?
> ...


what is the proper way to exhaust a bathroom fan? (through the roof or through a soffit)?


----------



## Rivethead (Dec 26, 2008)

Vent your bath fan thru the roof.


----------



## AtlanticWBConst. (May 12, 2006)

wilsonfrench said:


> Hi. I have installed the exhaust fan with a hose that expells the warm air through the a hole (which I cut) in the soffit....will this warm air be sucked back into the attic? ..thereby defeating the whole purpose of an exhaust fan?
> I Have peforated soffits..thanks


No. You are moving that moisture laden exhaust-air through mechanical, "active", or forced means. 

Soffit vents are static, or "passive" intake venting.

Additionally, that interior air that you are moving out, is generally warmer, and under most weather conditions: Warm air will rise, and move out & away from the underside of the soffits.


----------



## wilsonfrench (Dec 26, 2008)

*passive and active vents*



AtlanticWBConst. said:


> No. You are moving that moisture laden exhaust-air through mechanical, "active", or forced means.
> 
> Soffit vents are static, or "passive" intake venting.
> 
> Additionally, that interior air that you are moving out, is generally warmer, and under most weather conditions: Warm air will rise, and move out & away from the underside of the soffits.


...

so, I don't have anything to worry about? should I cover the soffits to the left and right of the exhaust vent (a pain-in-the-you-know-what) to get to because of its location (slope of roof and corner of house)...
I drew a photo to assist...even though you make clear sense...sounds like you have a lot of experience...however, could you explain how the soffits work? I thought that they suck up any air (warm or otherwise) around the soffits....
as such, I am not basically putting the warm air back into the attic? I know I have asked this two or three different ways...but I don't want to worry about it as I hate going up to the attic to potentially look for moisture. thanks (see photo)


----------



## Rivethead (Dec 26, 2008)

http://www.doityourself.com/stry/icedam


----------



## wilsonfrench (Dec 26, 2008)

AtlanticWBConst. said:


> The point of applying a vapor barrier onto insulation (facing the warm area) is about condensation/humidity from temperature change (cold air meeting warm condiitoned air). In the situation/arrangment that you describe, there should be some sort of vapor barrier between the insulation and the warm area (bathroom). Dependent on regional building codes, this may be required because of the cold air meeting warm (heated) air (aka = dewpoint condensation).
> 
> As far as vapor coming thru the ceiling's painted drywall surface, this just isn't going to happen. If you have an exhaust vent, properly installed, and venting the moist bathroom air to the outside, and a proper coat of mildew resistant paint, these should suffice to protect the drywall from any moisture.
> 
> ...


HI Atlantic, I am not sure of what the resolution should be...
do I install a VB on the warm side of the insulation (by going up into the joist bay)...
or do I not put any VB....
as for the sheetrock that was installed wihtout a VB...he took down the old drywall and the insulation fell down into the bathroom..it was not replaced...which is why I need it to get blown in now....
which brings me back to the original q..
VB in ceiling above shower? or no? 
thanks!


----------



## AtlanticWBConst. (May 12, 2006)

wilsonfrench said:


> HI Atlantic, I am not sure of what the resolution should be...
> do I install a VB on the warm side of the insulation (by going up into the joist bay)...
> or do I not put any VB....
> as for the sheetrock that was installed wihtout a VB...he took down the old drywall and the insulation fell down into the bathroom..it was not replaced...which is why I need it to get blown in now....
> ...


You should have a VB between the insulation and the warm side (bathroom) area.


----------



## Rivethead (Dec 26, 2008)

To the original poster I hope you don't mind but I need to ask a question here - due to everything I've read on this issue.

Folks - if he has a shower that now has blue board as the ceiling and we presume it was properly taped and mudded. Then he has tile over top of that on the ceiling - why would he need to try and retro fit a vapor barrier above that? 

Retrofitting a vapor barrier is recommended against on most sites I've seen. Let's say he does a really good job of placing plastic between the joists and taping in place to the sides to seal it. Isn't any moisture (which I doubt will migrate thru the set up he has) going to be trapped at the bottom of the plastic and simply soak into the edges of the joists that will still be exposed because of the retro fit.


----------



## AtlanticWBConst. (May 12, 2006)

Rivethead said:


> To the original poster I hope you don't mind but I need to ask a question here - due to everything I've read on this issue.
> 
> Folks - if he has a shower that now has blue board as the ceiling and we presume it was properly taped and mudded. Then he has tile over top of that on the ceiling - why would he need to try and retro fit a vapor barrier above that?
> 
> Retrofitting a vapor barrier is recommended against on most sites I've seen. Let's say he does a really good job of placing plastic between the joists and taping in place to the sides to seal it. Isn't any moisture (which I doubt will migrate thru the set up he has) going to be trapped at the bottom of the plastic and simply soak into the edges of the joists that will still be exposed because of the retro fit.


The vapor barrier would be for Thermal applications...if the poster is in a region of the country that requires "thermal-insulation" vapor barriers. 

The poster stated that there was no vapor barrier installed between the attic insulation and the bathroom ceiling. By Code, in colder regions, there needs to be, due to difference in temperature. The attic is a non-heated area (non-conditioned). The Bathroom is heated (conditioned).

When cold air meets warmer air, it creates condensation (Cold Coke Bottle reaction in summer = dripping wet surface glass).

It is the same application on ceiling areas in direct contact with unheated space (in certain colder regions), as it is with insulated walls = Use vapor barriers.

Example Links: 

http://www.powerhousetv.com/stellent2/groups/public/documents/pub/phtv_yh_di_000433.hcsp

http://www.bge.com/portal/site/bge/menuitem.5e8ef9b342df471021b08424025166a0/

http://homerenovations.about.com/od/houseexteriorframework/f/atticvaporbarri.htm


----------



## Rivethead (Dec 26, 2008)

Thanks for the additional information! So much out there that ends up on opposite sides of this issue. Look at this for example. There is also a GSA site that says adding a barrier after the fact is not worth while?

Hope the OP isn't totally confused - I've read reams of information on the topic and no where near done yet - but I sure am. 

http://www.naima.org/pages/resources/library/order/BI451.HTML


----------



## Chemist1961 (Dec 13, 2008)

Guys, didn't read the whole link, but Wilson lives in Ontario as do I. Due to our climate fluctuation vapour barrier is definately code on all exterior walls / ceiling new construction. Not sure if that blue board covers the entire ceiling but due to our extremes in temp -30 to +100 VB is the norm. we are also in one of the most humid ares of the country between 3 Great Lakes.


----------



## mwr1550 (Jan 29, 2012)

I have a smiluar problem I have an older home with lath and plaster cielings. There is no vapor barrier in the attic under the insulation. Due to a roof leak last year the cieling of the bathroom got wet and started to bow. The leak has been fixed but I want to install new drywall in the bathroom. Should I put a vapor barrier on top of the old cieling before I install the new drywall?


----------



## dberladyn (Apr 24, 2011)

If your house has no vapour barrier already... I wouldn't lose sleep over whether or not you should install one during a renovation that only covers 5% of your house.

I don't even want to get into this one because too many people have too many opinions. Also, I have no idea where you are or what's typical for your climate. I know here we use 6mil poly to create an air tight barrier witch COMPLETELY seals the warm living space. You're only doing the bathroom ceiling... 

If a vapour barrier is typical in your climate... put one in and seal it the best you can... but considering you don't have one in the rest of the house... I wouldn't worry too much. Mind you, you might have tar paper backed insulation. That was a form of a vapour barrier in the old days.


----------

