Ag exemption makes it commercial? I would have thought the Ag exemption requires very little.
We just got an exemption to build a barn up on property that is zoned "residential/agricultural". They had been telling me I can't build a barn on the lot without building a 950 sqft residence.. Blocked us for years. Yesterday I found a "loophole" that allows us to build a "barn" for "agricultural storage / processing" - by digging into the ordinances and zoning confirmed (verbal) approval so I can submit a plan for formal.
If I said I was doing "processing" that's "commercial" here and that's why the OP is getting stuck with a requirement like that. I'd encourage the OP to read the zoning regs very carefully, as commercial can often require things like fire suppression systems and ADA parking, and ADA baths.
Here they wanted to know that we'd be doing the lumber production locally and not importing materials (even though this is not stated in regulations). We harvest lumber (sometimes) - it's not really commercial. They wanted to know if we were running a business.
My learnings on building things like this:
1) Do not trust "word of mouth" of the authority. If you're doing some thing that isn't in their day to day they may be wrong. Read the ordinances and know 'em. Bring them copies of their ordinances when asking questions.
2) Don't trust contractors either unless they are VERY familiar with building in your area and are offering to do the permitting.
3) Look for similar structures within the boundaries of the authority. Here I can lookup their permits and you can get a LOT of useful information.
4) If they "require" something politely ask them to show you where such a requirement exists.
There's a GC for the house but I'm doing it myself for the shop.
Try designating this as an "accessory building". There may be ways to get around ADA if there is a residence going up. Typically you can't mix "commercial" and residential construction (there are exceptions). You aren't commercial, this building is an "accessory" to the main house and shouldn't have to comply with commercial specs in most areas... Not saying your area isn't different as they are ALL different.