Vapor Barrier Question - Insulation - Contractor Talk

Vapor Barrier Question

 
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Old 06-25-2013, 05:23 PM   #1
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Vapor Barrier Question


Doing a ceiling repair from a water leak in a 1950 vintage ranch home.. Went up into attic and removed the wet insulation above the repair ( about 75 sq ft) . There was loose rockwool insulation down first(about 2-3 inches) , then 3.5 inches of pink fiberglass batts on top inside the joist bays. Then across the top was 6 inches of pink fiberglass. No vapor barrier down against the ceiling. I dont want to mess around with the loose fill rockwool for the re-insulation, so I plan on just installing 6 inches of pink fiberglass between the joists and 6 inches across the top to match the existing thickness of the rest of the attic. Should I use unfaced down first against the ceiling or faced? Since the rest of the house has no vapor barrier Im thinking unfaced down first is the correct way?
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Old 06-25-2013, 06:25 PM   #2
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Re: Vapor Barrier Question


In our climate, you really ought to have a vapor barrier. While it might not be practical to redo the rest of the house, you can at least do the area you're working in the right way.

Bottom layer faced, second layer unfaced.

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Old 07-08-2013, 10:43 AM   #3
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Re: Vapor Barrier Question


Hi, Dale Rex. Im the senior research and development program leader at Owens Corning, so I wanted to see if I could provide some help as Ive done extensive work in this area.

To clarify, a vapor barrier is not required for your application that is, for a ceiling or attic insulation as long as your attic is well ventilated. Almost all houses have ventilation as a way for the attic to breathe. The ventilation carries away any kind of water vapor that makes it through the ceiling.

By the way, if youre moving around any of the existing insulation and you happen to see any locations where there is an opening this could be a source of air leakage, which is wasting energy. You should seize that opportunity to air seal that location with a sealant. (Full disclosure: we have a sealant called EnergyComplete.

Hope this information was helpful.
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Old 07-09-2013, 09:13 PM   #4
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Re: Vapor Barrier Question


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Originally Posted by DaveWolfOC View Post
The ventilation carries away any kind of water vapor that makes it through the ceiling.

By the way, if you’re moving around any of the existing insulation and you happen to see any locations where there is an opening – this could be a source of air leakage, which is wasting energy.
Uh... While the first part above is mostly true, vapor barriers also serve as air barriers. Is the product you recommend truly significantly more efficient at containing heat (while still allowing moisture to condense on cold attic areas)?
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Old 07-10-2013, 09:34 PM   #5
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Re: Vapor Barrier Question


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Originally Posted by DaveWolfOC View Post
To clarify, a vapor barrier is not required for your application that is, for a ceiling or attic insulation as long as your attic is well ventilated. Almost all houses have ventilation as a way for the attic to breathe. The ventilation carries away any kind of water vapor that makes it through the ceiling.
I forgot where I read it, but some university research stated that the only place for vapor barriers would be in wet areas, kitchens/baths. Some quality primers also serve a sufficient vapor barriers, then chunk on some paint.

We have a house where there's no vapor barrier in the ceiling, and the only place where the (original paint) is delaminating is above he stove...where there's no exhaust fan.
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Old 07-11-2013, 08:14 AM   #6
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Re: Vapor Barrier Question


Well vapor barriers have no business being in most houses & are pretty much slated to be removed from many existing climate zones in the 15 version of the building codes - the important thing is keeping the air from moving through the walls / ceiling, etc... which transports more moisture than diffusion could ever hope to in a lifetime

CO762 - major wet areas - back splashes, showers, etc... yes, the rest it is better to run the exhaust fans
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Old 07-11-2013, 05:03 PM   #7
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Re: Vapor Barrier Question


Some might even say there's no reason for a vapor barrier if one control some of the air flow...controlling not to be confused with containing.

What I find interesting is how a lot of folks say don't dump the bathrooms exhaust fan into the attic.....yet fans above stoves serve to be little more than stainless grease traps.

We are all different, but I've always viewed backspashes as a dry area unless in an institutional/commercial area, then it's stainless/FRP. But then again, I've seen more than a few showers with FRP walls......
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Old 07-11-2013, 09:45 PM   #8
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Re: Vapor Barrier Question


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Originally Posted by SLSTech View Post
Well vapor barriers have no business being in most houses & are pretty much slated to be removed from many existing climate zones in the 15 version of the building codes - the important thing is keeping the air from moving through the walls / ceiling, etc... which transports more moisture than diffusion could ever hope to in a lifetime
But what the heck is the difference?

Last year, we had an inspector tell us we didn't need a vapor barrier on the inside of a house because the foam board it was sheathed with served that purpose. Then he required us to use an air barrier over the fiberglass insulation in the walls. Plastic was just hunky-dory with him.

How is a vapor barrier not an air barrier? How is an air barrier not, at least to some [fairly large] extent, a vapor barrier? If air flows freely, so will water vapor. If air does not flow freely, neither will water vapor.
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Old 07-12-2013, 06:15 AM   #9
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Re: Vapor Barrier Question


Got kids CO762? It isn't a dry area in my place & not sure the issue on the kitchen exhaust though they do have filters to help slow down / prevent said buildup

Tin, good question - the answer in many respects is pretty easy, that is the wrong product for that application & it's being installed in the wrong place. Bur wait the exterior right? I mean it is installed under the cladding - true but there are a ton of gaps & spaces whether its vinyl, Hardi, Brick, etc... which will allow any water to drain out

On the inside we have drywall placed flat against the wall which is where you do want to stop the airflow, just like you do on the exterior at the sheathing. If you do get any water between the drywall & plastic, it is trapped & it cant dry out till summer time... It is much easier & better to stop unintended air leakage at the drywall (which by itself is an air barrier) & also at the exterior sheathing - for more on what an air barrier is: http://blog.sls-construction.com/2013/bs4d-air-barriers
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Old 07-12-2013, 08:42 AM   #10
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Re: Vapor Barrier Question


Some inspectors are on the ball, others are 8 ways of nerdlike goofy, and a small minority are seemingly clueless, just wanting to get out of the house/office, walk or drive around and visit with people. Ironic that at times we have to 'educate' inspectors. But to be fair, there are a lot of products out there.

Just my opinion, but whenever people boil water often and/or for a long period of time in smaller units, there should be an exhaust fan for that moisture as it's like a concentrated steam bath. If that blast of steamed water can be disbursed enough, then it probably wouldn't be a problem, but not my liking. But then again, with my cooking, at times I also set of the smoke detectors......
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Old 07-12-2013, 01:26 PM   #11
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Re: Vapor Barrier Question


Lots of products & new ways of doing things, shoot you think contractors don't like change...

In general the fan should be on as soon as they turn the burner or stove on (especially gas ones) & turned off once they are done - yep done that once or twice or... myself
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Old 07-12-2013, 06:29 PM   #12
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Re: Vapor Barrier Question


That's where in doing fluking residential remods, have those data sheets out and on the counter when the government paid socializer wanders in. He can educate himself later (?) as one continues to do actual work......
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Old 07-12-2013, 10:09 PM   #13
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Re: Vapor Barrier Question


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It is much easier & better to stop unintended air leakage at the drywall (which by itself is an air barrier) & also at the exterior sheathing
And why is it not a good thing to stop water vapor at both of those surfaces? If it can't enter from inside the house nor outside, how can a double vapor barrier be anything but a good thing? Water would never get into the insulation, and therefore never need to get out.

Oops, sorry, got off on a tangent there. Getting back to Inspector Guy, his point was that fiberglass does a relatively poor job of keeping air in stagnant little pockets; thus the need for air barriers on each side of it.

I actually agree with that. But I contend that there is no practical difference between a properly done double vapor barrier and a properly done double air barrier.

Your blog doesn't address this, unless I've missed something.
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Old 07-13-2013, 06:15 AM   #14
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Re: Vapor Barrier Question


You don't want a double vapor "barrier" just in case water does get in between, but you got it - it is best to stop or retard it at both those surfaces, not under them but where the water vapor would be

The other thing is as CO762 is bringing up, you also need to control the moisture you generate inside, by using bathroom / kitchen fans, etc...

You are correct, the article I posted does not really get into the vapor issue, as I have other pieces on just that & depending on how or what materials you selected - it maybe the same layer, or even another one.

Fiberglass, it actually does a great job when installed properly of keeping air in stagnant little pockets if there isn't to much of a temperature differential. Of course part of the installed properly requires no air leakage to short circuit it.
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Old 08-15-2013, 01:37 PM   #15
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Re: Vapor Barrier Question


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And why is it not a good thing to stop water vapor at both of those surfaces? If it can't enter from inside the house nor outside, how can a double vapor barrier be anything but a good thing? Water would never get into the insulation, and therefore never need to get out.
If you could install it perfectly it is fine. Reality is that doesn't happen. Moisture gets in via an area that it can't get back out through the double barrier. You've got mold or worse.

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