Hence, economical height limits for a particular building maybe below the local planning regulation. In which case it may be necessary to place the maximum number of stories within the permitted height, which will result in the thinnest type of floor possible being chosen. For example, soils with low bearing capacity and high compressibility will require large spread foundations to distribute the loading or may require piles in order to transfer the loads to a firmer strata. In which case, it may prove cheaper to increase span of beams in order to reduce the incidence of pile growth. On elevation building size may be low rise or multi-storey.
Units generally repeat vertically and horizontally.
Width and height may be multiples of the structural units leading to use of simple skeleton frame. Square - structural grid may result in two way spanning slabs. Long thin form - buildings on plan may result in one way spanning slab. Speed of erection. Availability of labour, etc.