45.—For the purposes of sections 46 to 57, “improvement” in relation to a tenement means any addition to or alteration of the buildings comprised in the tenement and includes any structure erected on the tenement which is ancillary or subsidiary to those buildings and also includes the installation in the tenement of conduits for the supply of water, gas or electricity but does not include work consisting only of repairing, painting and decorating, or any of them.