How many units makes it commercial?

I have a multi-unit building in which I’d like to upgrade the electrical service. The local building department said that I need an engineering drawing because the building is 4 units - which makes it commercial. My understanding is and always has been that 1-4 unit buildings are residential and OVER 4 units in a building is commercial.
I have looked at a lot of references and found a lot of anecdotal evidence to support my position, but nothing in writing from an authoritative source.

What number of units in a building makes it commercial? Anyone have a written source to back up their answer? I’m in Ohio is that matters.




Normal when the question is asked, “How many units make it commercial?” that is in relation to lending. This may be a case where the local building codes and/or zoning differ from the lenders’ definition. I would ask them to provide me with a written citing – they’re the government and that’s part of what they’re there for (e.g., to serve the public as public servants!)…remember your taxes pay them!


What county is the property in? Not that it makes much difference but some counties I am sure have variances in the guidelines for building codes.

As far as lending gos it’s anything over 4 units

Hi Mike,

I’ve sent you a PM with contact info of a person that might be able to help you.


Not sure if it changes from state to state or even county to county, but here in NJ 1-4 units are residential 5 and above are commercial.

Thanks for all your replies. I just got off the phone with an attorney from our REIA and she had a copy of the building code. Apparently, Keith is exactly right. The 1-4 units that I am used to seeing as residential applies to lending. The Ohio building code is apparently entitled something like The 1, 2, and 3 Family Building Code, and then there is a separate commercial building code. So, it looks like I will need an engineering drawing.