Is Zakat due on the rental income of a jointly-owned building before its sale?

If you acquired the building with the intention of possessing it, and then decided to sell it, zakat is not obligatory on the building itself. Rather, it is obligatory on its revenue if it reaches the nisab and a full year has passed over it. However, if its acquisition was with the intention of trading, then it is subject to the zakat of trade goods, and the rental income is subject to zakat along with the principal.