The flat roof in its construction
Compared to the common couple roof (inclined roof, monopitch roof, steeply pitched roof) the flat roof has none or only very slight roof pitches.
When planning a flat roof an incline of minimum 2% should be considered (which is 1.15°) according to the German standards institute (DIN) in order to be able to drain off rain water or melt water.
The low owned weight and the extended usage possibilities (e.g. for roof terraces) are aside from the cost effective production the most important advantages of a flat roof.
The construction of a flat roof can either be constructed as a cold roof (single-shell roof) or as a warm roof (double-shell roof).
The cold roof
The cold roof consists of two roof-shells that are installed in a distance to each other and is an internally ventilated roof. The air can circulate in the cavity between both roof-shells and inhibits moisture condensation. Due to the air circulation between the roof-shells, the roof prevents also an accumulation of heat in case of solar radiation. The roof does not heat up and the heat is not accumulated in the roof. The internal roof-shells have the maximum air temperature that is present in the shade.
The thermal properties of a cold roof as opposed to a warm roof are similar, with the same insulation thickness.
The cold roof requires a more elaborate execution as opposed to the warm roof; and therefore creates also slightly higher costs.
The warm roof
The warm roof consists of a single-shell roof structure, and there is no exhaustion and ventilation in the roof itself. The warm roof is a non-ventilated roof.
In the cold season the warm roof has similar insulation properties as the cold roof. However, in the warm season the warm roof heats up during longer periods of warm sunny weather. Due to the missing internal ventilation in case of solar radiation the heat cannot be dissipated and is stored in the roof. Therefore, the residential house heats up after longer solar radiation.
Sealing of a flat roof
The most important thing regarding a flat roof is the sealing. Only the slightest leakages can lead to moisture ingress and even worse to a big damage caused by dampness. The sealing of the flat roof must be 100% waterproof. The slightest damages must be repaired immediately, and therefore a flat roof is maintenance-intensive.
The typical sealing of a flat roof consists of asphalt cement. Asphalt cement is a tarry coating that you can find on roads. Asphalt cement is applied on the flat roof in continuous lengths and then flamed.
You can find additional articles helping you plan your house in our guidelines for house builders.
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