Replies

1. Expert Member
   MALCOLM TAYLOR | Apr 05, 2023 07:06pm | #1

   A432,

   Membrain is a variable perm vapour-barrier that moves from less than 1, to 20 when damp. OSB, acts in much the same way starting at 2, and can climb to 12 when damp.

   So yes, the presence of a layer of OSB on the interior will thwart the smart membrane. I'd leave out the Membrain, and let the OSB do the job. But I'd be interested to hear what other posters think given it's potentially very wet environment, and you end up with almost the same permeability on both sides of the wall.

1. 
   A423 | Apr 07, 2023 09:28am | #2

   Thank you for your response.
   Am I getting it right to say.
   Sandwiching OSB between drywall and Membrain won't hurt anything it's just a waist of time and money to put both up. The Membrain has a potentially higher perm rating (20) for inward drying then OSB (12) The potentially higher perm of Membrain is lowerd to 12 by the addition of OSB. At that point the only thing the Membrain would be doing is acting as a air barrier.
   I do like the structural integrity OSB would add to the wall.

1. 
   huey_ce | Apr 07, 2023 10:11am | #3

   I agree with Malcolms comment that the OSB limits the capabilities of the smart membrane so you might as well save the money and skip the membrane.

   My advice would be to swap the OSB for plywood. In my experience OSB takes longer to saturate and dry than plywood. Once it is wet it likes to stay wet and starts to deteriorate. Seen some research that agrees with this which blamed it on the additional adhesives and broken structure of wood chips vs peeled veneer.

   I cant seem to find the link at the moment, but my anecdotal experience of leaving scraps of OSB and plywood outside at home support this.

1. Expert Member
   MALCOLM TAYLOR | Apr 07, 2023 11:33am | #4

   Huey_ce,

   Probably a valid concern in a high moisture environment like a garage.

2. Expert Member
   MALCOLM TAYLOR | Apr 07, 2023 11:34am | #5

   A423,

   Yes.

1. 
   A423 | Apr 07, 2023 12:11pm | #6

   Thank's again for the sound advice and helping me make my mind up. The only other question I would have is, Do you have a recommendation ( does it matter) what type of plywood to use?

1. 
   huey_ce | Apr 07, 2023 01:27pm | #7

   What is the purpose of the extra layer of sheathing on the inside face of the wall? I am assuming the exterior sheathing is taking care of any wall bracing requirements. Is it just some extra strength so you can hang tools everywhere?

2. 
   A423 | Apr 07, 2023 02:19pm | #8

   What planted the seed in my head was looking at the wall with the garage doors. The wall is
   40' long and has (3) 10' wide doors in it. Tying the top plates, pony wall, header and
   rest of wall together with a sheet product would greatly strengthen the wall. Plus I may be putting side mount garage door openers in. So in a nutshell yes, extra strength. It should be okay without the interior sheeting since it is tied together on the outside. I just like the thought of added strength especially in that area. I have enough sheets of OSB to cover walls
   (I know just because I have it doesn't mean I need to use it). If I decide to I may just do the wall with the garage doors with plywood then membrain and drywall other walls. Hence me asking you guys your opinion so i can come to an conclusion based off your knowledge.

1. Expert Member
   MALCOLM TAYLOR | Apr 07, 2023 02:41pm | #9

   A423,

   Plywood is an even more effective variable perm vapour-retarder than OSB. Wherever you use either OSB or plywood on the interior there is no point in using Membrain.

1. 
   A423 | Apr 07, 2023 03:24pm | #10

   The only reason I mentioned OSB is because I have it. After are conversation I will not use OSB. If I decide to sheet, I'll use plywood and no Membrain. Is there any particular type of plywood that I should use?

1. Expert Member
   MALCOLM TAYLOR | Apr 07, 2023 03:32pm | #11

   A423,

   1/2" CDX.

3. 
   A423 | Apr 07, 2023 03:49pm | #12

   Thank you, I appreciate the education.