AskCodeMan

Codeman:

Is there language somewhere in the IBC that prohibits constructing a building across a property line?
Even if the properties are owned by the same person?

Not as such, that would be a zoning issue with setbacks.

There are some code sections related to property lines, but those section specify fire-resistance of the exterior walls versus distance from a property line.

An example is this:
- 412.2 Aircraft hangars. Aircraft hangars shall be in accordance with Sections 412.2.1 through 412.2.6.
- - 412.2.1 Exterior walls. Exterior walls located less than 30 feet (9 144 mm) from property lines, lot lines or a public way shall have a fire-resistance rating not less than 2 hours.

The walls would need to be rated for no less than 2 hours.

Here is another one in Appendix D, Fire Districts:
- D102.2.6 Exterior walls. Exterior load-bearing walls of Type II buildings shall have a fire-resistance rating of 2 hours or more where such walls are located within 30 feet (9144 mm) of a common property line or an assumed property line. (section continues with other information)

There are others, but those sections are not designed or intended for a structure which is constructed across property lines.

Typically, you would need to do a what is usually referred as a 'minor replat' and legally join the two property into one property before any area would allow you to construct a structure crossing a property line between two properties.

Also, no lending company would lend money on a building such as that as one lot could be sold and that half of the building would now belong to someone else.

I cannot think of any acceptable reason to construct a structure across a property line, but ... that would be up to zoning in your local zoning area, whether that is a county, city or a town.

Keep in mind that building codes are minimum standards, they do not address common sense or the lack of common sense, they are just the minimum one is required to build to.