The last I looked it up, I concluded the right answer was to bifurcate the property into 2 Sch E entries, one for the self-rental and one for the remainder. It's not all or nothing based on percentages, the way residential vs non-residential is.

That said, if the "his business" is not something that files a separate tax return (that is, if the business is a Sch C), and if "his LLC" also does not file a separate tax return (that is, the rental goes straight on Schedule E, rather than Ep2), actual expense for 50% of the building goes directly on Sch C, the 50% rented to other tenants is normal rental income and expense on Sch E, and the self-rental income / expense is entirely eliminated.