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glue, screw & vapor barrier?


Dingo2av8's Avatar
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01-30-06, 05:53 AM   #1  
glue, screw & vapor barrier?

I am building a new additon onto the exsisting, garage with room above in a canadian climate. The code calls for 6ml vapor barrier where any cold zone meets a warm including floor. I am going to glue and screw the ply to the joist. My question is " how do you put the vapor barrier in without disturbing the ply glue joist contact?" I hope you understand what I am trying to say.
Dingo

 
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doug thomas's Avatar
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01-30-06, 07:00 AM   #2  
Canadian code says that anything with a perm rating less than 45 ng will work (9.25.4.2.(1)), so long as you don't have anything low perm outboard of the insulation. If that happens, then you have to drop the interior perm rating to 15 ng (9.25.4.2.(2)).

In a wall system, the low perm outboard sheathing necessitates the use of 15 ng or less poly.

In a garage ceiling, drywall has a perm rating of about 500ng, so the PLYWOOD can satisfy the code requirement so long as it has a perm rating less than 45 ng.

Did that make sense?

 
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01-30-06, 08:16 AM   #3  
OK then

so what you're saying is no vapor barrier needed.

 
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01-30-06, 10:01 AM   #4  
So long as the floor has a perm rating less than 45 ng. Or even your floor finish, if you are using something like tile, or hardwood floors.

 
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01-31-06, 06:17 AM   #5  
Spray foam

I have heard that the spray foam acts as a vb and gives you an R 7 for every inch. It is just a little costly. Have you heard this?

 
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01-31-06, 06:59 AM   #6  
I know this.

Price matches performance.

Except in art.

 
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01-31-06, 09:55 AM   #7  
Posted By: doug thomas Canadian code says that anything with a perm rating less than 45 ng will work (9.25.4.2.(1)), so long as you don't have anything low perm outboard of the insulation. If that happens, then you have to drop the interior perm rating to 15 ng (9.25.4.2.(2)).

If you are referring to the National Building Code, this is only a model for the Provinces to create their respective Codes. The local inspector will respect the Provincial Code, not the NBC.

Dingo, you need to follow what is stated in your Provincial Code. Which province are located in?

And, as I always say, the Codes are quite simply, "the worst way to build a home which will pass Code". That is why is says "mininum requirements". It is always better to improve on the Code.

 
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01-31-06, 12:37 PM   #8  
Thanks for the advice Em69, but it's also in the provincial codes as well. You are welcome to look it up for your location in Ottawa.

I would like to know however, what benefit you see to adding a vapour barrier under the floor deck? What's the winter condensation plane? There is none. All you'd be doing is providing the means for interior humidity to accumulate in the floor deck and raise its moisture content.

As for improving on code, it is important to realize that poly is dangerous; it does a poor job of keeping moisture out of places you don't want it, and a very good job of preventing things from drying once they are wet.


Last edited by doug thomas; 01-31-06 at 12:55 PM.
 
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02-02-06, 04:22 AM   #9  
Regardless of how the Code is worded, 6 mil poly is one fo the few acceptable "materials" for a vapour barrier in most Canadian provinces. Your "solution" would never pass inspection in Ontario.

 
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02-02-06, 06:14 AM   #10  
It has and it does.

 
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02-02-06, 05:37 PM   #11  
Wow! Congratulations on finding a way to build something that meets the "minimum" standards. You seem proud with that distinction.

Not even builders (who do everything possible to save money) would even consider doing this. Go figure.

 
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02-03-06, 06:13 AM   #12  
Em69
You seem to misunderstand.

Being able to eliminate the vdr improves the quality of the assembly, it doesn't reduce it.

You seem to have the notion that polyethylene is a benefit in buildings. Unfortunately, that isn't the case, especially in air conditioned buildings. The canadian & provincial codes even have a caveat in place that excludes them from fault in the event that polyethylene causes moisture problems in air conditioned buildings. It's Section A-5.5.1.2.(1).

Meanwhile, your government is spending millions paying special consultants to develop alternative construction methods that can exclude polyethylene while still preventing condensation problems. Ever been to a government conference? All they talk about is how to eliminate vapor barriers.

This white paper, a simplified version of an article published in ASHRAE in 2004, includes some of the assemblies that have been developed through this work:
http://www.buildingscience.com/resou...r_Barriers.pdf

A quote:
"So What is The Problem?
Incorrect use of vapor barriers is leading to an increase in moisture related problems. Vapor barriers were originally intended to prevent assemblies from getting wet. However, they often prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. This can be a problem in any air-conditioned enclosure. This can be a problem in any below grade space. This can be a problem when there is also a vapor barrier on the exterior. This can be a problem where brick is installed over building paper and vapor permeable sheathing."

 
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02-03-06, 10:26 AM   #13  
Sorry!

I didn't mean to create such controversy, I just want my floor built. Decided to use 5" of spray foam only with 5/8 ply on floor, 5/8 drywall on garage ceiling.
Thanks for all your help
Dingo

 
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