24 C.F.R. § 891.560 – HAP contract.

(a) HAP contract. The housing assistance payments contract sets forth rights and duties of the Borrower and HUD with respect to the project and the housing assistance payments.
(b) HAP contract execution.
1. (1) Upon satisfactory completion of the project, the Borrower and HUD shall execute the HAP contract on the form prescribed by HUD.
2. (2) The effective date of the HAP contract may be earlier than the date of execution, but no earlier than the date of HUD's issuance of the permission to occupy.
3. (3) If the project is completed in stages, the procedures of paragraph (b) of this section shall apply to each stage.
(c) Housing assistance payments to owners under the HAP contract. The housing assistance payments made under the HAP contract are:
1. (1) Payments to the Borrower to assist eligible families leasing assisted units. The amount of the housing assistance payment made to the Borrower for an assisted unit leased to an eligible family is equal to the difference between the contract rent for the unit and the tenant rent payable by the family.
2. (2) Payments to the Borrower for vacant assisted units (vacancy payments). The amount of and conditions for vacancy payments are described in § 891.650. The housing assistance payments are made monthly by HUD upon proper requisition by the Borrower, except payments for vacancies of more than 60 days, which are made semiannually by HUD upon requisition by the Borrower.
(d) Payment of utility reimbursement. As applicable, a utility reimbursement will be paid to a family occupying an assisted unit as an additional housing assistance payment. The HAP contract will provide that the Borrower will make this payment on behalf of HUD. Funds will be paid to the Borrower in trust solely for the purpose of making the additional payment. The Borrower may pay the utility reimbursement jointly to the family and the utility company, or, if the family and utility company consent, directly to the utility company.