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What are the pros and cons of moving (or omitting) a self-adhered water control membrane in an assembly using exterior wood fibre board insulation?

andyfrog | Posted in Energy Efficiency and Durability on

I noticed that on there really aren’t any articles regarding exterior wood fibre board insulation, so I went down a Google rabbit hole and discovered a few different ways it’s being used in assemblies:

1. There are a handful of videos from Europe where the self adhered WRB is applied directly to the exterior face of the wood fibre board. For the air control layer, some of these have taped plywood on the interior, some of them have a sheathing with a pre-applied air control membrane (kind of like interior ZIP sheathing I suppose, but not exactly), and some put up Intello on the interior. I don’t really understand the differences between these three air control approaches. These are in northern Europe.

2. there’s Ben Bogie’s video where they’re using taped plywood on the interior for the air control layer, and then they just have the wood fibre board on the exterior with no self adhered WRB. I don’t know if the insulation seams get taped or not, or if it’s even necessary. This is in New England.

3. there’s another video where they’ve put the self adhered WRB on the exterior of the sheathing, and then mechanically fastened the wood fibre board to the membrane surface. This is in California.

All three of course have furred rain screens as the outermost layer of the assembly.

I can’t really figure out what the mechanistic differences are between these three options. I would imagine #2 is the most vapor open, followed by #3. But I don’t really know if any of these differences make a significant performance difference.




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