Replies

1. GBA Editor
   Martin Holladay | Jan 30, 2013 03:20pm | #1

   Erik,
   There's some information on your question in a GBA article, Choosing a Cost-Effective Wall System. In that article, Scott Gibson reported:

   “Malcolm Taylor writes that the British Columbia building code allows an “airtight drywall air barrier” instead of polyethylene. “Illustrated details covering all aspects of the approach can be found in the Building Envelope Guide for Houses published by the Homeowner Protection Office, which is a Provincial Government department,” he says.”

2. 
   user-1105327 | Jan 30, 2013 03:58pm | #2

   this is where it gets confusing: the inspector has never even mentioned air barrier. most everyone i know assumes the poly is both AB and VB. and if detailed correctly probably works well enough. i suspect i could use lumber wrap as the AB for all he cares as long as i use poly as the 'vapour barrier'

3. Expert Member
   MALCOLM TAYLOR | Jan 30, 2013 09:55pm | #3

   Hi Erik,
   The BC code does distinguish between Air and Vapour Barriers and spells out the properties each must have. Sheet goods can be used as Air Barriers as long as they meet the building code maximum air leakage rate of 0.02 L/s.m2. (and both plywood and OSB do). The code also allows any material to be used as a vapour barrier which has a vapour permeance of less than 60 ng/Pa.s.m2 (1 perm). Sorry I don't know if plywood or OSB meet this without a vapour barrier paint or not. But in either case there is no restriction on using sheet materials, and no injunction that poly must be used.

   Your BI is probably a dinosaur like me who has to be dragged into this new way of thinking about building envelope design, but the BC code doesn't!

   The 2012 has come into effect. I haven't seen it yet but any changes are likely to further relax the vapour barrier restrictions not increase them.

   As an aside: I don't know if you are in coastal BC but the new code has brought in very prescriptive seismic requirements which will dramatically change the way you have to design and build.
   http://www.bccodes.ca/Illustrated-Guide-For-Seismic-Design-of-Houses.pdf

4. 
   user-1105327 | Jan 30, 2013 10:32pm | #4

   hi malcolm, thanks for the reply. i have scoured the 2006 edition and cannot for the life of me find any language that suggest you can use any product you want as long as it meets their requirement of 60ng. my interpretation is it must be <60ng and one of or combination poly, membranes, wall coating.
   i agree the code distinguishes between air and vapour barriers, however, i was suggesting most assume they are one and the same. in fact, the inspector kept asking me--multiple times--why i should be allowed to build without a VB when i suggested using something other than poly.
   as far as the vapour permeance of 5/8" osb, i have literature from the plywood council of bc stating it passes the standard test for <60ng. for example, 1/4" cdx plywood is rated at 40ng dry cup.

5. 
   user-1105327 | Jan 30, 2013 11:07pm | #5

   malcolm, the gist of my reply was meant to ask if you know where in the 2006 bcbc it states explicitly or implicitly that you can use any product for a VB as long as it satisfies the vapour permeance requirement? thanks again..

6. Expert Member
   MALCOLM TAYLOR | Jan 31, 2013 12:10am | #6

   Hi Erik. I think the key section is 9.25.3.5.(1) (b) "Vapour Barrier Sheet, Excluding Polyethylene for use in Building Construction".

   And:

   The Appendix (A-9.25) which provides an overview as to acceptable approaches to satisfying both the air and vapour barrier requirements states in reference to interior finishes: "...these techniques often require no separate vapour barrier but rely on appropriate paint coatings to give the interior finish sufficient resistance to water vapour diffusion that it can provide the required vapour barrier protection. The wording of this Section allows for such innovative techniques, as well as the more traditional approach of using a continuous sheet such as polyethylene to act as an air/vapour barrier".

   A more detailed gloss on the requirements can be found in the BC government publication "Building Envelope Guide for Houses".

   With reference to Vapour Barriers:
   1.0 (10 of 13) "The BCBC allows for any of these materials (with a vapour permeance of less than 1 perm) to be used as the required vapour barrier in a wall system"

   With reference to Air barriers:
   1.) (11 of 13) "Air barriers are typically made from standard construction materials which are joined and sealed together. Any material that meets the building code maximum air leakage rate of 0.02L/s.m2 can be used as part of an air barrier system."

   So my interpretation of these is that if your plywood, OSB or drywall meets these two criteria it is both the required air and vapour barrier. Hope this helps.

7. 
   user-1105327 | Jan 31, 2013 04:48pm | #7

   it does help, thanks, malcolm...
   were you quoting 9.25.3.5.(1)(b) and appendix (a-9.25) from the 2006 edition?