(13)Where appropriate, classes of performance in relation to the essential characteristics of construction products should be encouraged to be used in harmonised standards, so as to take account of different levels of basic requirements for construction works for certain construction works as well as of the differences in climate, geology and geography and other different conditions prevailing in the Member States. On the basis of a revised mandate, the European standardisation bodies should be entitled to establish such classes in cases where the Commission has not already established them.