Flat roof or pitched roof? Pitched roofs were the most common type of roof for centuries. It was only with the invention of plastic-based waterproofing and the start of modernisation in the middle of the 20th century that flat roofs became a popular alternative. Both variants have their advantages and disadvantages and so, in addition to design and economic issues, building-specific features must also be taken into account at the outset. Another important aspect is the climatic conditions at the location. The definition of a "flat roof" is specified as < 10 ° in accordance with the flat roof guideline. Architecture Flat roofs adapt better to complex floor plans in particular and give the building a modern appearance. The straight walls make it easier to furnish with conventional objects. The additional options for utilising roof areas, especially as roof gardens, roof terraces or play areas, offer an extended range of uses and climatic advantages in urban areas. The floor below can be illuminated using skylight domes.With pitched roofs, on the other hand, the cubic volume behind can be used in combination with dormers to create additional usable space. Its classic shape can be interpreted in a modern way and create a special appearance with rectangular floor plans. Costs A comparison of two detached houses between pitched and flat roofs carried out by TU Wien in 2015 showed that constructions with pitched roofs are more cost-efficient in the long term than buildings with flat roofs. The calculation included costs for all life cycle phases - i.e. production, operation and replacement of the components at the end of their service life. The maintenance of flat roofs is more complex than that of pitched roofs, but the initial costs of a pitched roof are higher. The possibility of extending a pitched roof and the resulting gain in space relativises these additional costs. Technology The biggest advantage of pitched roofs is the safe drainage of rainwater on the outer skin. This prevents standing water from forming, which increases the risk of mould and moisture damage on flat roofs. From a structural point of view, pitched roofs are more resistant to wind, as there is less suction effect, but their higher dead weight requires more foundation measures. In areas with higher snow loads, this advantage can diminish as the snow remains on the flat roof. The smaller the roof covering, the less surface area it offers for wind to attack. The most important aspect of flat roofs is by far the waterproofing, which must always be laid professionally. This can be made of foils, bituminous sealing sheets or liquid PVC. To summarise, all three aspects must be taken into consideration in order to make a decision about the roof shape.