When does flipping homes in a SD IRA create UBTI?

[Scott Jensen]

I am reading mixed things online about the tax implications of flipping homes inside of a self-directed IRA. When is a non-financed house flip inside of a SD IRA or Solo(k) subject to UBIT? Is one flip ok? One flip per year? Multiple flips? What if you are primarily a house flipper vs working primarily in an unrelated business? Is there any case law for this? What sections of the tax code or IRS guidelines are you relying on?

@Brian Eastman @Dmitriy Fomichenko @George Blower