What Building Code Applies to Post Frame Construction?

Being a Plans Examiner in a Building Department would have to be one amongst this planet’s toughest jobs. Besides having to listen to clients who have their own ideas about how things should be built, there are volumes upon volumes of Building Code books and referenced texts.
A Hansen Pole Buildings’ client in Arizona recently had some extended discussions with a Plans Examiner in regards to appropriate Building Code for a residential detached accessory post frame building. Plans Examiner really wanted governing code to be 2012 IRC (International Residential Code). Of course all of this becomes confusing and confounding to this future building owner, as he had initially verified Code information with this same Building Department
previously and was advised 2018 IBC (International Building Code) would be applicable to his structure.
IRC has no language in it pertaining to post frame construction, while IBC indeed does. Your Building Department may require this building to be designed under IRC version 2012, even though later versions have greater accuracy for structural design due to advances in research and technology. This has to do with local jurisdiction code adoption policy.
Let’s look at how latest (2021) Codes handle what Code actually applies.

2021 IRC R101.2 Scope.
“The provisions of this code shall apply to the construction, alteration, movement, enlargement,replacement, repair, equipment, use and occupancy, location, removal and demolition of detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress and their accessory structures not more than three stories above grade plane in height.”
2021 IBC 101.2 Scope.
“The provisions of this code shall apply to the construction, alteration, relocation, enlargement, replacement, repair, equipment, use and occupancy, location, maintenance, removal and demolition of every building or structure or any appurtenances connected or attached to such buildings or structures.
Exception: Detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress, and their accessory structures not more than three stories above grade plane in height, shall comply with this code or the International Residential Code.”

2021 IRC R301.1.3 Engineered design.
Where a building of otherwise conventional construction contains structural elements exceeding the limits of Section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice. The extent of such design need only demonstrate compliance of nonconventional elements with other applicable provisions and shall be compatible with the performance of the conventional framed system.
Engineered design in accordance with the International Building Code is permitted for buildings and structures, and parts thereof, included in the scope of this code.

Building a ‘barndominium’ or post-frame home or an accessory structure to a barndominium or post-frame home? Then IRC governs. Building an accessory structure when a home is not present on same parcel, then IBC governs.