How many preliminary notices do I need to send for a North Carolina duplex?

Generally, a residential property being a duplex vs. a single-unit won't change how many preliminary notices are required. So, if a preliminary notice is required for that type of project, then the fact that it's a duplex won't affect the number of notices required. After all, it's still just one property. If there were multiple, separate properties being improved under the same contract or subcontract, then that might enter into the multiple-notice territory. But even then, it's possible that one notice could be sufficient if it's substantially the same project with the same owner and GC.

As for what notice is required - keep in mind that a Lien Agent won't be required if the project is less than $30,000. So, it's possible a lien agent isn't present, and if that's the case, a Notice to Lien Agent would not be required. Still, a Notice of Subcontract could be required (for both subcontractors and suppliers) if the GC has filed a Notice of Contract document.

For more discussion on North Carolina's preliminary notice rules, here are some articles that should be helpful:

North Carolina Preliminary Notice FAQs
North Carolina Preliminary Notice: Everything You Need to Know