Insulation Thickness

bwilliams

Renovating 1 1/2 storey home. Kitchen ceiling was insulated. 2X6 joists across the top. Should I use 2X4 Roxul or 2X6 Roxul to insulate the ceiling followed by vapor barrier. Just wondering about airflow. 2X6 Roxul will fill the void between kitchen ceiling and tongue and groove flooring above the joist. Thoughts????

Windows on Wash

Where is the home located?

You don't need to insulation between conditioned spaces if that is what you are doing.

If the T&G is the attic floor, get as much insulation as you can up there because 2x4 or 2x6 construction does not give you anywhere enough depth.

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jklingel

you probably don't want a vapor barrier, either. if you MUST, then make sure it is on the warm side of the insulation. air seal as best you can.

bwilliams

I'm in Ontario Canada. There has to be insulation there. It is a storey and a half house and other than the roof itself, there is no other place to put insulation. I took insulation out when we dropped the ceiling. It had a layer of pink and then a bagged yellow insulation. I believe at one time, the bag was the vapor barrier. Why would I not want a vapor barrier. I thought that was the thing, to seal the home

jklingel

Canada apparently requires a vapor barrier. As far as I know, the bulk of the rest of the world does not. Vapor retarders (something that will pass a little bit of water vapor) are usually code in the US (one perm or less). Air sealing can be done quite effectively without a vapor barrier, and air sealing is what is important. VB's can be problematic, esp if you run an air conditioner; probably not necessary in most of Canada. If both sides of a wall/ceiling are heated, then the need for insulation is strictly for noise control unless there is a reason to keep one side warmer than the other.

Canucker

The National Building Code of Canada specifies that vapour barriers are not
required when:
“it can be shown that uncontrolled vapour diffusion will not adversely affect any of,
(a) health or safety of building users, (b) the intended use of the building, or (c) the
operation of the building services.” We always require the installation of an air barrier, unfortunately most contractors throw up the 6 mil poly to meet the requirements for both.
And you're right, its over kill and usually unnecessary when you can meet the requirements with 2 inches of ccPSF.

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jklingel

Thanks for clarifying that. I find it interesting that "vapour diffusion" is mentioned, as diffusion is not the culprit, but rather vapor traveling through leaks (according to building science, and it makes sense to me). From what I have read, far more water migrates through a 1" hole in sheet rock than diffuses through a 4x8 sheet. Maybe "diffusion" was used as kind of a generic word for "movement". Either way, thanks for the code.

bwilliams

Okay so we have that established. Kidding, but seriously though, does anyone have an answer to my question?

jklingel

IF YOU HAVE ventilation above your insulation (and you have not yet articulated exactly the whats/wheres), then use 6" Roxul and a vapor barrier if you don't want to use a vapor retarder and argue w/ the inspector. Either way, AIR SEAL. Poly is nice for air sealing, but it may cause problems if the seams are not taped and/or gooed w/ acoustical sealant, if you don't seal in and around electrical boxes, top and bottom plates of walls, etc, etc.

Canucker

It probably is just a generic term for vapour movement. It was part of a research study done for the sprayfoam industry by some members of the buildingscience crew for vapour barriers in above grade walls. Pretty much confirms everything you pointed out about faulty air sealing being the main culprit for failure. I can give you the link to it, if you'd like.

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jklingel

[QUOTE=Canucker;965819Pretty much confirms everything you pointed out about faulty air sealing being the main culprit for failure. I can give you the link to it, if you'd like.[/QUOTE] Good to know I have not been reading lies all this time. No need for the link, thanks. I've read enough on the subject that I will not be using any vb's again. We are too cold and too dry to worry about it.

Windows on Wash

+1 jk.

I always look at this picture when I think about air movement vs. diffusion.

75X more on air than on diffusion.

Airtight is right.

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jklingel

windows: good pic. source? size of sheet rock? thanks. j

Windows on Wash

http://www.energysavers.gov/your_hom.../mytopic=11760

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Gary in WA

ftp://ftp.cmhc-schl.gc.ca/chic-ccdh/..._Web_sept5.pdf

Gary

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