Origin: Widespread in Vietnam since the late 20th century with reinforced concrete townhouses and modern architecture.
The flat-roof house has a reinforced concrete roof, usually with a slight fall for drainage, forming a usable terrace. The front is clean and modern and works well with louvres and balconies. Costs are reasonable and adding a storey later is easy.
Its big weakness is heat and leaks. With hot northern summers, a flat roof needs insulation such as hollow bricks, foam boards or a ventilated secondary roof above. Waterproofing must be done carefully with a bitumen membrane or cementitious coating, with upstands and drains detailed. In damp humid coastal regions, slope the roof about 1 to 2 percent to the outlets and make parapets tall enough to shield wind.
