Flat roof
Flat roofs (abbreviation FD ) are roofs with a roof pitch of less than 10 °. Some sources cite an upper limit of 5 ° (8.8%).
There is no clear statement about the pitch of flat roofs in German building regulations .
In the 1st Federal Immission Control Ordinance (1st BImSchV), the TA Luft, as well as in the guidelines VDI 3781, Part 1, the definition of minimum chimney heights between roofs with a roof pitch of less or a maximum of 20 ° (= flat roof) and a roof pitch from or more than 20 ° (= pitched roof).
As a rule, the roof cladding of flat roofs is used as a roof seal . From a slope of about 10 °, roofing made of roof tiles or concrete roofing tiles is also possible in exceptional cases.
history
Flat roofs were already known in ancient times. Already around 3000 BC According to Herodotus, bitumen was used as a building material. Especially in arid areas, this type of construction corresponded to the climatic conditions. If the problem of sealing is solved satisfactorily, it can be used as a roof terrace. In the 6th century BC The Hanging Gardens of Semiramis , one of the seven wonders of the ancient world , emerged in Babylon . The waterproofing in this case consisted of layers of asphalt slabs, bricks and mortar.
The garden culture of antiquity was revived during the Renaissance in Florence, Rome and Venice. Roof areas on castles became roof gardens. In the Baroque era, Jakob Marperger (1656–1730) advocated green roofs.
Outside the European building tradition, flat roofs from India to the Arab countries to the pueblos are part of the traditional construction method, whereby the roofs are often used as roof terraces.
Architectural theorists such as Bernhard Christoph Faust were already promoting flat roofs at the beginning of the 19th century . Supported by “beams and battens, consisting of two layers of tiles pounded together with black pitch. Advantages of these roofs: good shape of the houses, strength, durability and fire safety, more security against lightning strikes. ”Gaining an additional floor without changing the construction height would also bring“ good interest ”, and when building flat roofs“ a lot of expensive timber could be used can be saved ”. In 1839 Samuel Häusler developed the wood-cement roof , which was popular in large cities. In 1867, Carl Rabitz published the brochure "Natural Roofs of Volcanic Cement" and advocated the idea of the green flat roof.
Between the First and Second World War, the flat roof was the subject of dispute between the representatives of the “New Building” or the Bauhaus and the conservative architecture of the homeland security . The latter, for example Paul Schmitthenner , rejected the “Bolshevik-Jewish” flat roof for ideological reasons, Le Corbusier , on the other hand, advocated it with doctrinal intensity, although it initially emerged that in Central European climatic conditions the flat roof did not always offer ideal results (for example in the case from Le Corbusier's Villa Savoye ). In the 1950s, the flat roof finally caught on.
Since then, flat roofs can be found in all types of buildings, from single-family houses to apartment blocks, prefabricated buildings and high-rise buildings, from commercial and administrative buildings to churches. Flat-roof bungalows and apartment blocks, for example, were defining elements of West German architecture in the 1960s and 1970s.
Advantages and disadvantages
Advantages of flat roofs with roof sealing compared to pitched roofs with roof covering :
- Low weight of the roof skin
- Extended usage options ( e.g. roof terraces , green areas , parking decks, installation and easy accessibility for technical equipment, use of solar energy)
- Exposure option for interior rooms, e.g. B. by skylights
- Inexpensive
- If necessary, the building can be added later.
- With the same eaves height , greater light incidence on the property is possible, especially when the sun is low in the winter months.
But flat roofs also have some disadvantages:
- As a rule, they are less durable and more maintenance-intensive than pitched roofs.
- They are more sensitive to aging and moisture damage.
- Sealing materials such as bitumen and plastics are more problematic in production and disposal than metal roof coverings, roof tiles or roof tiles.
- In the regions with large amounts of snowfall, a significantly reinforced roof structure is required or the roof must be cleared regularly.
- Compared to a building with a sloping roof, the same stand area and comparable usable or floor space , the incidence of light on the property is restricted by the higher eaves .
construction
Structure
With flat roofs in multi-storey buildings, the uppermost space-enclosing floor slab is normally part of the roof structure. Mostly it concerns reinforced concrete solid slabs, profile sheets or reinforced concrete structures. Sealed flat roof surfaces are also possible on sloping wooden roof structures, albeit less often. The roof structure and the roof structure are mutually dependent and must be viewed as a unit during planning.
construction
Flat roofs are designed as warm roofs (non-ventilated roof), cold roofs (ventilated roof) or as inverted roofs with external thermal insulation. In the case of renovations, the lower, old roof can also remain, and a new structure is then built on top (DUO roof or "PLUS roof"). This is more cost-effective, especially in the case of a renovation, since the very high demolition costs can be saved. However, this design should be checked technically, object-related.
Slope / roof pitch
The DIN 18531 roof waterproofing divided flat roofs in the roof slope group I inclination of up to 3 ° (5.2%) and roof inclination group II with inclination of 3 ° (5.2%) to 5 ° (8.8%).
The flat roof guidelines recommend a slope of at least 2% (1.1 °) in the area and 1% in the roof valleys . In order to largely avoid stagnant water caused by accumulation of snow or leaves, for example, a slope of 5% (2.9 °) should be provided.
In exceptional cases, such as intensely green roofs, backwater may be desirable so that there is no slope here.
Free backwater is usually undesirable because
- Together with UV radiation, it can damage soft building materials such as bitumen sheeting in the long term ("mud cracking")
- the growth of red algae can lead to incrustations
- it can cause embrittlement through plasticizer migration of plastic sheets
- When exposed to sunlight, greater temperature differences occur between moist and dry areas and lead to thermal stresses.
With sufficient load-bearing capacity of the roof, thermal stresses and UV radiation can be kept away from the waterproofing by means of a gravel layer, paving or roof greening .
seal
Protection against ingress of water is provided by the rainproof roof covering on the pitched roof , and the waterproof roof sealing on the flat roof . In addition to tightness, the state building regulations require extensive requirements for resistance to flying sparks and radiant heat in accordance with DIN EN 1187 B roof t1 . Typical materials for sealing flat roofs are bitumen welding sheeting (nowadays usually plastic-coated) and sealing and plastic roofing sheets .
Bitumen roof seals have proven themselves in the market for many years, as the seams are simple and can be easily checked visually. A distinction is made between plastic (PYP) and elastic (PYE) modified bitumen sheets, which have different material properties: Plastic bitumen sheets have a high resistance to the effects of heat, but weaknesses in resistance at cold temperatures. They are widely used in the Mediterranean. Elastic bitumen sheets tend to have strengths in terms of their cold bending behavior and are mainly used in Central Europe. Bituminous seals have the particular advantage that subsequent reworking z. B. for additional penetrations for air conditioning, etc. is unproblematic.
EPDM waterproofing membranes made from ethylene-propylene-diene monomer have proven to be more durable and more resistant . As with any roof waterproofing, it is assumed that the seams are properly processed by a skilled craftsman. A clear advantage is the far lower number of seams compared to other forms of roof waterproofing. The EPDM waterproofing membranes are produced up to a size of 15.25 mx 61 m. The area of application extends from Scandinavia to Australia and from Canada to Chile.
In the meantime, injected liquid plastics are often used in renovations for cost reasons. The advantage of liquid plastics is that they can be applied seamlessly without a joint, are highly elastic and can be applied to all surfaces. They are applied with a two-component hot spraying and dosing system with reaction times of 2–15 seconds depending on the material.
Plastic roofing membranes made of PVC, PE, EVA, PIB or thermal polyolefins are sometimes to be considered independently. This is also evident from EN 13956, which provides for different test values than for EPDM geomembrane .
So-called flat roof tiles can also be used, for which, however, a standard roof pitch of 22 ° applies, so that a roof covered with this is no longer counted as a flat roof according to the current definition.
In addition to the seals mentioned, roof coverings made of metal ( stainless steel , zinc , copper , lead, etc.) are also possible. Double standing seam roofs can be professionally produced according to the technical rules for the plumbing trade with additional measures from a roof pitch of 3 °. A roller-seam-welded stainless steel roof is not only watertight, but also gas-tight and can even be made without a slope. This process is not only used for new buildings, but also for the renovation of leaky flat roofs.
drainage
Flat roofs have to 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 work using gravity drainage:
- Free slope drainage with the pipeline system laid on a slope.
- (Under) pressure drainage with fully filled pipelines as planned. (The pipeline system does not need a gradient if it runs horizontally.)
Special shapes
A special form of the flat roof is the coffin lid roof, which is bevelled on the sides. See also platform roof or old roof . The wet roof is no longer common today .
literature
- E. Cziesielski, H. Marquardt: Textbook of building constructions . 3. Edition. BG Teubner , Stuttgart 1997.
Web links
- Baunetzwissen.de
- FR flat roof | 2016-12 : Technical rule for waterproofing - Flat roof directive including amendment 2019-05
Individual evidence
- ↑ flat roof . In: Bibliographisches Institut (ed.): Meyers Enzyklopädisches Lexikon . tape 11 . Mannheim / Vienna / Zurich 1973, ISBN 978-3-411-01258-9 , pp. 848 .
- ^ OLG Munich judgment of June 8, 2004, Az. 1 U 1976/04.
- ↑ Zehlendorfer roofs war. (PDF; 6.7 MB) Retrieved June 17, 2016 .
- ^ Ernst Piper : Combat League for German Culture (KfdK), 1928–1934. In: Historical Lexicon of Bavaria . June 17, 2016. Retrieved June 17, 2016 .
- ↑ For the history of the flat roof cf. http://www.baunetzwissen.de/standardartikel/Flachdach-Geschichte-des-Flachdachs_155933.html , accessed on May 13, 2013.
- ^ Structure and mode of action of flat roofs , accessed on June 19, 2012.
- ↑ Information about flat roofs. Beautiful living , accessed on June 19, 2012.
- ↑ a b Michael Schäfer: Flachdach - The water has to go , dachbaumagazin 4 | 2018
- ^ Flat roofs in stainless steel , Deutsche Bauzeitung - Bautechnik, DBZ 06/2005
- ↑ Vacuum drainage ( Memento of February 13, 2018 in the Internet Archive ), Basics and planning information, pp. 124–126, ACO-Haustechnik.de