Concerned about Water Vapor in new wall assembly
Hello folks, really appreciate this forum.
We’re building a modular home at zomes.com. This is a CAD of our latest model: https://autode.sk/3VeAzdT
Our wall assembly is composed of the following layers from the EXTERIOR to the interior:
1. (outermost) 1/2 inch fiber cement board
2. 1/2 inch zip board structural pan
3. 1.5 inch continuous rigid insulation
4. 3 inch douglas fir frame with 3 inch rockwool comfort board in the insulation
5. 1/4 inch interior decorative panel
We are wanting to replace the 1/2 inch zip board with a 1/2 inch MgO structural panel. The concern being raised is that the MgO panel may not be breathable. And will therefore trap moisture from inside the building, which will condense from the inside of the board, and get trapped there. Creating mold on the framing.
My limited understanding of vapor is that it won’t get trapped on the inside and will diffuse back into the building.
Can anyone shed some light on this?
Here are the relevant spec sheets:
Magnesium oxide panel:
Rigid insulation: https://drive.google.com/file/d/1ybYdAP32vcI5uoPPDu4bHvxh7lTuJFq4/view
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