Fitness of materials and workmanship

In any relevant work— (a) the materials used shall— (i) be of a suitable nature and quality in relation to the purposes for and the conditions in which they are used; (ii) be adequately mixed and prepared; (iii) be applied, used or fixed so as adequately to perform the functions for which they are designed; and (iv) not continue to emit any harmful substance longer than is reasonable in the circumstances; and (b) the standards of materials and workmanship need be no more than are necessary to— (i) secure the health, safety, welfare and convenience of persons in or about the building; and (ii) further the conservation of fuel and power.