So…writing this here just as a means of documenting to remember.
We found out that our next door neighbors have been fighting M/I about mold. They closed on their house on Dec 31. Shortly after they saw black mold on the floor joists in the basement. M/I had it professionally mitigated.
Then the neighbors samples air moisture in their wall cavities and it was 21%. Higher than what they say is the max allowable of 20%.
Talked to our builder and his story is similar to the neighbors but that moisture in wall cavities is normal for winter construction. They said the houses need a good year to dry out.
More to come as we learn more.