I find it interesting that a "definition" has become a code requirement. Normally, if I am looking for a code requirement I am not inclined to look in definitions. However, in 2006 the ICC changed the definition of Accessory Building to include the limitation of 3,000 sq. ft. in floor area in the definition and I find that limitation in no other part of the IRC.And, in the 2009 IRC, it further states that "the use of which is customarily accessory to and incidental to that of the dwelling".
I recently was sent to final a 12,000 sq. ft. accessory building to a "proposed?" (construction not begun) residential dwelling, in an area zoned residential. I'm new here and just adapting to the native mindset. Inside this "residential accessory building" I was surprised to see 2,000 sq. ft. of framing for office space (according to the owner who accompanied me). There is no plumbing, HVAC, or electrical to the building (remember, I am there to conduct a final inspection of a residential "accessory building"). This is an 80' X 150' X 20' high metal building. The residential lot is 10 acres. I halted the inspection (not knowing the local habits) and defered to the building official. I think this is going to P&Z or board of adjustments.
I'm curious to see how the use of this structure is going to be considered "customaily accessory to and incidental to that of the "proposed" dwelling.