Flat roof (roof terrace)

A flat roof, or roof terrace when people use it, looks level but is laid to a slight fall that carries rainwater to outlets or gutters. Its surface may be used only for maintenance, or turned into a sitting terrace, a green roof or a zone for plant and equipment. It is one of the most familiar elements of modern architecture.

The layers of a flat roof

In a conventional warm roof, the structural slab is topped with a screed laid to falls, then a vapour control layer, thermal insulation, the waterproofing membrane and finally a protective layer or finish. In an inverted roof, the membrane sits below the insulation, and water-resistant insulation boards shield it from sunlight and physical damage. Whichever system is chosen, the critical points are the same: enough fall, well-placed outlets and overflows, waterproofing turned up the parapets, and a proper coping. A flat roof that leaves standing water will leak sooner or later. If people will walk on it, the finish must be laid without harming the waterproofing.

Flat roofs in visualization

In aerial images, the flat roof is the building’s fifth facade. Gravel, paving, planting or the arrangement of equipment gives it character; leaving the roof as a plain grey plane is often the weakest point of a bird’s-eye view.