Notice to owner.

The said subcontractor or other person employed by the contractor as aforesaid, besides filing a notice with the Recorder of Deeds of the District of Columbia as aforesaid, shall serve the same upon the owner of the property upon which the lien is claimed, by leaving a copy thereof with said owner or his agent, if said owner or agent be a resident of the District, or if neither can be found, by posting the same on the premises; and on his failure to do so, or until he shall do so, the said owner may make payments to his contractor according to the terms of his contract, and to the extent of such payments the lien of the principal contractor shall be discharged and the amount for which the property shall be chargeable in favor of the parties so employed by him reduced.