A residential investment property is considered a section 1231 property by the IRS. A section 1231 property is a business property that was held for more than one year. Rental property not included in section 1231 is single-tenant triple-net property. This is property that's leased 100% to a single tenant and that tenant is responsible for all property expenses. If you're unsure if your property qualifies for section 1231, you should consult with a real estate or tax professional.