flat roof

A flat roof is a nearly horizontal roof designed with a slight pitch for water drainage. Historically, flat roofs were common in arid climates where water drainage was less critical. With advancements in waterproof materials and structural engineering using steel and concrete in the 19th century, flat roofs became more practical and widely adopted for commercial, industrial, and residential buildings.12

Modern flat roofs often feature highly water-resistant coverings. Traditional options include built-up membranes made of coal-tar pitch and felt, typically layered and ballasted with gravel. More recent innovations include single-ply roofs made from plastic membranes, with seams welded together and secured by ballast or mechanical fasteners. These roofs are usually pitched at very shallow slopes, between 1:100 and 1:50, directing water towards interior drains.3