Mold Potential in Wall Assembly? – GreenBuildingAdvisor

Hello,

I recently built a house from Nelson Homes with their “energy wall” but have discovered that the foam board they used is Halo Interra which is quality product but is vapor impermeable and I really think they should have used a permeable foam. 

The assembly from outside to inside is:

1. Vinyl siding

2. Tyvek

3. 7/16″ OSB

4. 1-3/4″ GPS with foil facing

5. 2×6 stud bay with R-23 fiberglass batt

6. Poly vapor barrier

7 . Drywall

We are in climate zone 6B, so cold but fairly dry. The record high dew point is 60F.  

The wall assembly is similar to Zip R except the toe board and window/door openings are 2×8 so the OSB is in direct contact with the framing there. Also it came as a panelize kit  so the edges of the foam board coincide with the edges of the OSB. A couple things I have going for me is that since construction was slow there was plenty of time for the lumber to dry out. I don’t have plumbing in the walls and I didn’t observe any bulk water entering over the course of a year. If you were to use the foam as a vapor barrier they call for the seams to be taped which they are not.

There is a video and diagram of their wall assembly process here to get a better idea of how it goes together:

https://nelson-homes.com/design-engineering/engineering/

Is this a safe assembly? I did put a humidity sensor in the wall at the foam face in one spot and it stays as 45%-50% all the time regardless of outdoor conditions. I assume the framing is buffering but I can’t tell if moisture is accumulating or not and it sort of points to it not being permeable at all.