This is a very unique situation. I will use an example to illustrate my response.

E.g. A couple owns a corner store, and lives in the upstairs of the building. So the downstairs was their store and the upstairs was their principal residence. The couple decides to retire, and sold their business along with the building in 2016. They sold the building for $1M.

In this example, the couple will apportion part of the proceeds to their principal residence and part to their business. Assuming the residence occupied 50% of the building, then $500,000 was their proceeds for their principal residence. And if it was their principal residence for all the years they occupied it, then the $500,000 for their residence would be completely exempted. You will need to report this on the pages related to Principal Residence.

The other $500,000 that's apportioned to the business will need to be reported as part of the business sale.