Tennessee Code Title 13. Public Planning and Housing § 13-19-102

(a) The state code for energy conservation established by this chapter shall govern the design and construction of new buildings and structures or portions thereof and additions to existing buildings that provide facilities or shelter for public assembly, educational, business, mercantile, institutional, storage, and residential occupancies, as well as those portions of factory and industrial occupancies designed primarily for human occupancy by regulating their exterior envelopes and the selection of their heating, ventilating and air conditioning systems, service water heating, electrical distribution and illuminating systems and equipment for effective use of energy.

(b) The state building commission shall utilize solar hot water heating systems if cost-efficient over the term of the bonds in any projects that involve conventional hot water systems.