If such order is not complied with, or so far complied with as the board may regard as reasonable, within five days after service or attempted service or within any shorter time, which, in case of imminent peril to the public health, the board may have designated, or is not thereafter speedily and fully executed, then such order may be executed as any of the orders of the board or department. Any agency of the city is authorized to act as agent of the department in executing such order. In the event that any agency shall so act, it shall certify and transmit to the department its expenses in the execution of such order separately in respect of each separately owned parcel of property. Such expenses shall be reimbursed to such agency and shall be chargeable and collectible as expenses of the department in connection with the execution of an order as referred to in this chapter.