(a) Allowable depreciation for the residential treatment facility will be a continuation of the Department of Social Services depreciation schedule previously in effect unless the commissioner determines error(s) had been made in that calculation. This requirement may be waived by the commissioner if the circumstances involved are found by the commissioner to be reasonable, necessary and in the public interest with respect to the facility.

(b) When an institution converts only part of its capacity to a residential treatment facility, allowable depreciation for the facility will be based on the historical cost and useful life of the specific building(s) being converted.

(c) The square footage used to determine allowable capital-related costs will be as determined by the commissioner in connection with his project approval authority under the Mental Hygiene Law and Part 551 of this Title. When only a portion of a building is being converted to a residential treatment facility, the percentage of approved square footage to total square footage for the building will be used to determine capital-related costs of the residential treatment facility.