In addition to any other lawful method for the provision by an authority of facilities incidental or appurtenant to a project, a municipality may in connection with any project of an authority, upon approval by the local legislative body, contract with an authority for the preparation of plans and construction by the authority for the municipality, as part of a combined occupancy structure, of a social, recreational, health, educational, or other non-housing facility or facilities deemed by the municipality and the authority to be incidental or appurtenant to such project, including material and equipment customarily provided in connection with such facility and required for the operation thereof, and for the conveyance, grant or surrender in fee of its interest in the facility or facilities by the authority to the municipality upon reimbursement of the authority by the municipality for all costs incurred by the authority for development of the facility during construction or upon conveyance thereof. The authority and the municipality may provide for, grant and reserve such easements, space rights and air rights as they may deem necessary to effectuate the project and complete the facility. The cost of any such non-housing facility or facilities to be built by the authority for the municipality, which cost is to be reimbursed by the municipality to the authority, shall not be included in project cost for the purpose of determining the amount of periodic subsidies, if any, to be paid by the state for the project pursuant to § 73 (State subsidies)section seventy-three of this chapter. Notwithstanding the provisions of any other general, special or local law to the contrary, such contract may provide that the authority shall have sole charge and control over the plans and specifications for and the construction and supervision during construction of such facility or facilities; provided that the plans and specifications for and the construction of the project and the non-housing facility or facilities shall be subject to approval of the agency or agencies of the state and municipality having jurisdiction thereof as provided by law. The authority shall in constructing such facility or facilities comply with the requirements of this chapter. As used in this section “combined occupancy structure” shall mean any improvement on real property including fee interests, easements, space rights or air rights, containing a non-housing facility or facilities in combination with the residential portion of a project and intended to increase from both a planning and economic viewpoint the effective utilization of available land areas. A combined occupancy structure shall also include a structure in a project or development under the auspices of the authority wherein housing portions of structures placed upon the overall site are not built in space rights over the non-housing portion, so long as some part of the housing portion is constructed over the non-housing portion. The foregoing authorization shall be in addition to any existing powers of an authority or municipality under this chapter, and is not intended to nor shall it impair any existing powers of an authority pursuant to this chapter to provide non-housing facilities deemed incidental or appurtenant to a project, and to operate such facilities or lease the same to a municipality or agency thereof, public or non-profit body, or other person or corporation, for such operation or use.