The building sector is often subdivided into residential, commercial and institutional buildings. Commercial buildings include low-rise retail buildings and high-rise office towers, but could also include (depending on one’s definition) multi-unit residential buildings – condominiums and apartments. The institutional sector includes government buildings, hospitals, schools and universities. Many buildings in the institutional sector share similarities with commercial buildings. Thus, the distinctions between residential, commercial and institutional buildings are somewhat blurred and arbitrary. For this reason we shall lump institutional buildings with the commercial sector, so that henceforth we shall refer to just the residential and commercial sectors.