A flat roof is a low-pitched roof whose weatherproof outer layer is generally a continuous roof waterproofing layer. It may be unused, accessible, greened, or fitted with equipment or photovoltaics, and requires a coordinated drainage and maintenance concept.
What is a flat roof? Function and classification
The build-up protects the building despite slower water drainage. Waterproofing, insulation, vapour barrier, falls, drainage and details work together as a system.
Practical use
The load-bearing structure and falls are formed, followed, depending on the system, by a vapour barrier, thermal insulation, waterproofing, and protective and wearing layers. Junctions, penetrations and outlets are integrated with particular care.
Build-up and system variants
Typical constructions are unventilated roofs, ventilated roofs and inverted roofs. Uses range from gravel and green roofs to terraces, equipment roofs and solar roofs.
What should be considered in practice?
‘Flat’ does not mean omitting falls without planning. Water flow, emergency drainage, wind uplift, fire protection and maintenance access must be planned early; details have a decisive influence on durability.
Current technology and development
A revised version of the German Flat Roof Guideline has been available since January 2026. Water retention, combined solar and green roofs, and safe maintenance routes shape current planning.