Whenever the owner of any land or building fails to execute any work which he is required to execute under this Act or any bye-law made thereunder, the occupier, if any, of such land or building may with the approval of the Commissioner, execute the said work and he shall, subject to any contract between the owner and occupier to the contrary be entitled to recover from the owner the reasonable expenses incurred by him in the execution of the work and may deduct the amount thereof from the rent payable by him to the owner.