need advice concerning vapor barrier - Router Forums
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post #1 of 63 (permalink) Old 07-24-2015, 04:27 PM Thread Starter
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Default need advice concerning vapor barrier

I'm going to be doing some renovation to a frame and stucco house with a sprayed foam roof. The reno will include removing the drywall from two rooms, installing rigid foam (polystyrene) insulation, sealing the edges and voids with spray foam and re-drywalling the rooms.

The question is: Where does the vapor barrier go? I've heard that it is to be installed on the warm side of the wall while my neighbor, who's a contractor, says on the cold side.

Who's right? And why? Could either of us be confusing the Tyvek house wrap with a vapor barrier?
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post #2 of 63 (permalink) Old 07-24-2015, 04:35 PM
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the polystyrene is the vapor barrier...
it's in the right place for vapor barrier...

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #3 of 63 (permalink) Old 07-24-2015, 04:49 PM
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Yes. The Vapour barrier goes on the inside; the Tyvek on the outside. Tyvek is NOT a vapour barrier!
In fact, just the opposite. It breathes water vapour through it, but not water itself. In other words a molecule of H2O in vapour form can pass through Tyvek but a water droplet can't.
You probably should check with your Building Dept. re your local Code requirements regarding 'rainscreen'.
Here (Canada) it's mandatory and very closely inspected. Condo rot focused a lot of attention on this issue.
The pic below shows a system for commercial or highrise construction, but the principles the same for residential...
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post #4 of 63 (permalink) Old 07-24-2015, 04:56 PM Thread Starter
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Thanks, guys, that's very helpful.
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post #5 of 63 (permalink) Old 07-24-2015, 05:44 PM
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Any more vapour questions, Chuck, we're here 24/7...
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post #6 of 63 (permalink) Old 07-24-2015, 05:59 PM
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@sfchuck ...
Dan meant to say vapor

This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
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post #7 of 63 (permalink) Old 07-24-2015, 06:03 PM
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If Dan had meant to say "Vapor" he'd have driven down to Blaine Washington.
https://www.google.ca/search?q=vapou...AsL1-AHr4I2oAQ
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post #8 of 63 (permalink) Old 07-24-2015, 06:20 PM
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Quote:
Originally Posted by DaninVan View Post
If Dan had meant to say "Vapor" he'd have driven down to Blaine Washington.
https://www.google.ca/search?q=vapou...AsL1-AHr4I2oAQ
may be you should have...

British vapour. a visible exhalation or noxious gas...
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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
Stick486 is online now  
post #9 of 63 (permalink) Old 07-24-2015, 06:27 PM
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One of the escape routes for vapour is through light outlets and plug in receptacle. I spray foamed some wiring when I installed a range hood quite a few years ago. I recently changed the hood and found that the spray foam had dissolved the outer layer of insulation on the wire loom. The insulation on the individual wires was still fine, different plastic I would guess. You might want to use a latex based foam for around the wiring.

The Canada building code also classes rigid insulation as vapour barrier especially if you finish sealing it the way you intend. The reason for the vapour barrier going on the inside of the wall is to keep the vapour inside the house from getting into fibreglass, cellulose, or any other insulation that is capable of holding vapour. Once those types of insulation get wet the R value goes waaay down. Also, if it's cold, the dew point at which the vapour will condense into water is somewhere between the outside of the wall and the inside. This leads to mold and mildew which are serious health hazards as well as eating up the structure of the house over time.

Of course if you are in the States then you are dealing with water vapor which, according to Stick, is something completely different.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #10 of 63 (permalink) Old 07-24-2015, 06:37 PM
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Quote:
Originally Posted by sfchuck View Post
I'm going to be doing some renovation to a frame and stucco house with a sprayed foam roof. The reno will include removing the drywall from two rooms, installing rigid foam (polystyrene) insulation, sealing the edges and voids with spray foam and re-drywalling the rooms.
PL 300 is your friend here..
glue your panels up to the studs and the insulation board seams together for a complete VB......
use the stuff as caulk if the need arises..

Foamboard Adhesive PL 300 VOC from Loctite Adhesives
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This would have been the week that I'd have finished chewing thru the restraints...
If only new layers hadn't been added....

Stick....
Forget the primal scream, just ROAR!!!
"SNORK Mountain Congressional Library and Taxidermy”
Stick486 is online now  
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