Flat roof

Flat roofs (abbreviated FD) are only have a low or lower than 25 ° roof pitch with no or (more often) roofs. There are different limits, is spoken to those of flat roof:

  • Germany: up to 25 ° ( 44.0 %)
  • Austria: up to 5 ° (8.8%)
  • Recommendation flat roof guidelines: at least 2 % (1.1 ° ), better 5% ( 2.9 ° )
  • DIN 18531 roof waterproofing Roof pitch group I: up to 3 ° (5.2%)
  • Roof pitch group II: 3 ° (5.2% ) to 5 ° (8.8%)

In the German state building codes there is no clear statement to the roof slope of flat roofs.

In the first Federal Emission Regulation ( 1 BlmSchV ), the Clean Air Act, as well as be in the guidelines VDI 3781, Sheet 1 in the setting of minimum chimney heights between roofs with a roof slope of less than or at most 20 ° ( = flat roof) and a roof pitch distinguished from above by more than 20 ° ( = steep roof ).


Flat roofs were already known in antiquity. As early as 3000 BC they used according to the testimony of Herodotus bitumen as a building material. Especially in arid regions corresponded to this design climatic conditions. If the problem of sealing is satisfactorily resolved, a use can take place as a roof terrace. In the 6th century BC in Babylon arose about the Hanging Gardens of Babylon, one of the Seven Wonders of the World. The seal in this case was composed of layers of asphalt tiles, bricks and mortars. The garden culture of antiquity was revived during the Renaissance in Florence, Rome and Venice. Roof areas in castles were to roof gardens. In the Baroque period came Marperger Jacob (1656-1730), a vegetated roof surfaces. Already at the beginning of the 19th century flat roofs of architectural theorists such as Bernhard Christoph Faust were propagated. Worn by " beams and battens, consisting of two layers of tiles that are gepicht with black Peche together. Advantage of these roofs. Shapeliness of houses, strength, duration, and fire safety, more security against lightning " to change the recovery of another floor without the height, would pose " a good interest rate ", also could the construction of flat roofs " much dear lumber saved be " 1839 developed Samuel Häusler the wood cement roof, which became widespread in large cities. 1867 published Carl Rabitz the brochure" Nature roofs of volcanic cement " and defended it with the idea of green flat roof. During the interwar period, the flat roof was dispute between the representatives of" new building " and the conservative homeland Security architecture. the latter, for example, Paul Schmitthenner rejected the " Bolshevik- Jewish " flat roof for ideological reasons from, Le Corbusier took it, however, with doctrinal intensity, initially, however it turned out that in Central European climate conditions, the flat roof is not always ideal results offered ( as in the case of Le Corbusier's Villa Savoye ). In the 1950s, the flat roof sat through final.


In the 1960s and 1970s flat roofs were used mainly in bungalows. Over the past few decades but it has been used mainly for commercial buildings. By introduced in recent years, passive houses, the flat roof is now increasingly being used for residential construction.

Flat roofs are to be found in all types of buildings. Advantages of flat roofs with sealing against sloping roofs with roofing:

  • Low weight of the roof covering
  • Extended Licenses option (for example, rooftop terraces, landscaped areas, parking decks, installation and ease of access for technical units )
  • Exposure opportunity for indoor application, such as by skylights
  • Creative freedom in plan ( for future expansion )
  • Economical

Flat roofs also have some disadvantages:

  • They are very maintenance intensive.
  • It often occur on aging damage and moisture damage.
  • Required sealing materials such as bitumen or plastics are not particularly environmentally friendly.



For flat roofs, in multi-storey is the ultimate space-enclosing basement ceiling is normally part of the roof structure. Usually it involves reinforced concrete solid sheets, profile sheets or reinforced concrete structures. On gently sloping wooden roof constructions sealed flat roof surfaces are also possible, although less frequently. Roof structure and roof structure are interdependent and must be considered when planning unit.


Flat roofs are as warm roof ( non-ventilated roof), as a cold roof ( ventilated roof ) or as an inverted roof executed with external thermal insulation. During the renovation, also the lower, old roof, remain, then it is a reconstruction is made (DUO roof or " PLUS - roof "). This is more cost effective, especially in a restructuring, because the very high demolition costs can be saved. This version, however, should be strictly technical, object- based, tested.


The protection against the ingress of water takes over the sloping roof, the rainproof roofing, flat roof when the roof watertight seal. In addition to the tightness of comprehensive requirements for resistance to flying sparks and radiant heat according to national building regulations are required by DIN EN 1187 B roof t1. Typical materials for the sealing of flat roofs are bitumen membrane (now plastic generally remunerated ) and sealing and plastic roofing sheets.

Bitumen roofing membranes have been proven over many years in the market, since the splicing is simple and easy can be optically controlled. Here we distinguish between plastic ( PYP ) and elastic ( PYE ) modified bitumen membranes, which have different material properties: Plastic bitumen membranes have a high resistance to heat, but weaknesses in the resistance at low temperatures. They are often used in the Mediterranean. Elastic bitumen membranes have more strengths in Cold bending and find vast application in Central Europe. Bituminous seals have the particular advantage that is the later post-processing eg for additional penetrations for air conditioning systems, etc. problems.

As more durable and more resistant to EPDM waterproofing membranes have proven of ethylene -propylene -diene monomer. A rule- oriented processing of the seams by a skilled craftsman is required as with any roofing. A clear advantage is the much lower seam number compared to other roofing types. The EPDM waterproofing membranes are produced x 61 m up to a dimension of 15.25 m. The field of application ranges from Scandinavia to Australia and Canada to Chile.

In the renovation now for cost reasons very often sprayed liquid plastics are used. The advantage of liquid plastics is that they are applied seamlessly without a join, are highly elastic and can be applied to all surfaces. They are depending on the material, applied with a two-component hot- injection and metering system, with reaction times of 2-15 seconds.

Plastic roofing sheets made ​​of PVC, PE, EVA, PIB or Thermopolyolefinen are to be considered partially independently. This is also evident from the EN 13956, which provides for other test values ​​than with EPDM waterproofing membranes.

It can also be used flat roof tiles which are subject to a standard roof pitch of 22 °.

Apart from said seals and roof coverings of metal (eg, stainless steel) are possible. Doppelstehfalzdächer from fully recyclable construction metals are according to professional standards, professionally produced for the Plumbing Home with additional measures to 3 ° roof pitch. A roll seam - welded stainless steel roof is not only waterproof, but gas-tight and can even be made ​​entirely without any slope. This method has been successfully used not only for new buildings, but also in the restoration that have become leaky flat roofs.


Flat roofs must be drained in several places. According to DIN EN 12056-3 and VDI guideline 3806, there are two types of flat roof drainage. Both types operate by gravity drainage:

  • Gravity- drainage: The piping system is installed in the slope.
  • Scheduled full pipes: The pipe system is laid in a horizontal course without any slope.


A special form of the flat roof is the coffin lid roof, which is tapered at the sides. See also platform roof or arbor roof.