Thank you very much for your professional opinion, jy101.

I kind of understand that it is possible that lumber has mold during storage or transporation, etc.

I feel it is possible that if there is only a few spots of mold on the lumber and the builder use it.

However, when the lumbers are covered completely by mold and my builder still used it to build a $1m house, I feel the builder is not taking good care of the customers, in term of the house quality and potential risk to health.

jy101, what do you think my concern from a builder's perspective? Thanks you very much.