Replies

1. 
   charlie_sullivan | Apr 18, 2021 09:56pm | #1

   We used site-milled horizontal board sheathing plus diagonal bracing. We foolishly tried to use a Mento heavy duty WRB for air sealing at the exterior and it was hard to detail that to make a real air barrier, but our primary air barrier is interior, so it's not a disaster. Taped polyiso should do better, if it's in good enough shape to tape well. A self adhesive WRB should do better than either, I would think.

1. 
   maine_tyler | Feb 03, 2022 09:27am | #6

   I know this is an old post... but Charlie, what made detailing the Mento difficult / ineffective? Might be looking at similar options...

1. 
   charlie_sullivan | Feb 03, 2022 05:34pm | #7

   Here's my thinking. With a free floating membrane, if there's a little tear in a membrane anywhere, that becomes a leak that size. On the other hand, if there's a tear in the self adhesive membrane, and it's on top of a board, there's no air leakage. It's only when the holes line up with the cracks between boards that you get leakage. There's also the fact that sealing the membrane to the sill plate, for example, requires the tape to stick to the membrane, and the membrane to stick to the wood, so that's two points for possible failure. And if you have wind before the siding is up, the whole expanse of membrane is a sail pulling on that possibly questionable interface.

   If partly depends on your contractors skill level and learning ability. Mine had trouble understanding that tape doesn't stick to dirty surfaces. The success level with a free-floating membrane might be higher with more skilled contractors.

2. Expert Member
   MALCOLM TAYLOR | Apr 18, 2021 10:01pm | #2

   Luke,

   We often re-use the 1"x8" boards we used to form up the foundation walls as diagonal sheathing. That's easier here because we still use an interior air/vapour barrier, but you can do as you suggest and use the foam, or use an adhered WRB.

   Sheathing with boards is a task I hate. If they aren't long enough you have to taper the ends at the studs they join at, and trim the ends where they overhang the plates. There is a lot of waste and it is tedious, slow work.

   That said there is nothing wrong with the finished product. It's a good durable sheathing that isn't as susceptible to moisture problems as plywood or OSB.

3. 
   lrs123 | Apr 19, 2021 03:45am | #3

   Thanks for the responses.

   I agree that a self adhered WRB would be ideal, but that makes board the same price as taped osb with more work. I supposed i could do air tight drywall as a secondary barrier.

   Charlie - did you happen to have raised heel trusses on your build? I'm wondering how I'd address that with horizontal boards (or diagonal for that matter). Also did you use 1x or 2x for the let ins?

4. 
   Jon_R | Apr 19, 2021 09:41am | #4

   Consider not using wood sheathing at all - just diagonal steel strapping if required for racking.

5. 
   lrs123 | Apr 19, 2021 05:34pm | #5

   Good suggestion, Jon. I hadn't considered it because it's not common around here but no reason not to I guess.