Flat roofs can be differed in the material (Bitumen or Synthetics) as well as in terms of building them ether in single-layer (non-vented) or double-layer (ventilated). For single-layer roofs a barrier layer is first sealed on the roof to prevent the diffusion of moisture to the insulation above. Thermal insulation can be made of various materials (polystyrene, polyurethane, rock wool, cellular glass). The final sealing follows above the insulation and is made of bitumen (multilayer type) or synthetic sheeting (single-layer).

To prevent flat roofs to be blown off by storms a load often is brought on the rooftop. These loads often derive from the planned use of the flat roof: