Who to hire to check building code compliance?

[Tammy Mason]

I’m in contract on a duplex in a small city. Title shows it as a single-family. City has minimal permit records (only back to the 1980s). No permits found for the single-family to duplex conversion.

Old permit docs from the 1980-90s show the building was already converted to duplex, so it was likely converted before then. Planning says zoning is fine, but I’m worried the 2nd unit was never permitted.

City told me they will only send out inspectors if there’s a complaint. Who can I hire to check if it’s up to code?