Loan to purchase commercial buildings is partially secured by a dwelling. Is this HMDA reportable? I know a dwelling used to purchase a dwelling would be but since the purchase is a commercial building, I wasn't sure.

No it is not HMDA reportable unless the "commercial" building are residential property such as investment 1-4 family or multi-family.

If it is commercial property such as a store, office or factory, the loan is not HMDA reportable.

A refinance of such a loan, if still secured by the residential real estate, would be HMDA reportable if to the same borrower.