What are the layers on a roof

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Flat roofs are rightly considered to be uniquely diverse. A diversity that has two sides: on the one hand, the almost unlimited design options, and on the other, the high, specific requirements for insulation and sealing. It is the needs-based quality of the structure that determines the safety and service life of the roof area. It forms the basis for all architectural open spaces on the flat roof - from the roof terrace to the green roof.

Warm, light and green roof
Whether on solid reinforced concrete or a light substructure - the non-ventilated warm roof construction is the best solution on a flat roof. The compact sequence of layers reliably protects the thermal insulation from moisture. At the same time, their mechanical resilience opens up the greatest possible freedom in the use of the roof area: from the walk-on roof terrace to intensive greenery. The lightweight roof is particularly technically demanding. Substructures made of steel, wood or aerated concrete serve as an inexpensive flat roof variant. Due to their construction, such lightweight roofs place particularly high demands on the quality and flexibility of the roof waterproofing. With high-quality system solutions, a similarly long service life can be achieved here as with the solid roof made of reinforced concrete. The green roof offers blooming landscapes. The additional wear layer on the roof provides tangible advantages: to compensate for sealed surfaces, they store precipitation and provide fresh air and also protect the roof from UV radiation and extreme temperature fluctuations.

Glued, screwed, two-ply or one-ply

The appropriate roof structure is based on the existing or planned roof substructure and the use of the building. Roof packages with all their layers are often glued or welded with bitumen on concrete substrates. As a rule, two-layer bitumen waterproofing is used for this. On substrates made of trapezoidal sheet metal, the layers can be simply screwed mechanically to the substrate individually or in a package - this method of fastening has become established. The seal is then often made in a single layer with plastic sheeting. Two-layer bitumen seals offer better protection against mechanical loads than single-layer plastic seals.

Vapor barrier, insulation and waterproofing

The typical structure of a flat roof consists of the vapor barrier, insulation material and sealing layer or layers. In order to reliably prevent the penetration of moisture from the interior into the roof structure of non-ventilated flat roof structures, vapor barriers with an sd value of 1,500 m are usually used. For this purpose, bitumen sheeting with a special aluminum insert is welded onto the substrate on concrete substrates. Thinner self-adhesive bitumen sheets are suitable for trapezoidal sheet metal substrates - applied using the cold adhesive process and with significantly shorter processing times than with welded sheets. The seam connections and connections of vapor barriers to penetrations and adjacent components must be made airtight to function properly. The regulations and requirements for thermal insulation are constantly increasing. This also increases the demands placed on the insulating materials and their performance and / or their thickness. In order to still be able to use the thinnest possible material, products with good, i.e. low lambda values ​​are necessary. The high-performance insulation material polyurethane rigid foam is characterized by a very good thermal conductivity level. The current EnEV requires a U-value of max. 0.20 W / (m²K) for the renovation of a flat roof: In order to meet this value, an aluminum-laminated PIR insulation board (WLS 023) with only d = 120 mm is sufficient. Insulation materials for flat roofs must also be pressure-resistant enough to withstand the sealing and subsequent maintenance work. They must not give in too much under the weight of the craftsmen and also not allow themselves to be compressed so much that walkways with depressions arise. Here, too, rigid PU foam proves to be suitable: The insulation material can even be used without restrictions for roof surfaces such as terraces.

Sealing - two-layer or single-layer
Temperature, humidity, mechanical loads and environmental influences - to protect the roof, the waterproofing is laid in two layers with bitumen sheeting or one layer with plastic sheeting. In the case of bitumen waterproofing, the individual layers are glued together and thus secured against lifting. In the case of plastic seals, the wind suction is secured by mechanical fastening in the substructure. In the first layer of the roof waterproofing, robust polymer bitumen or quick-to-lay welding sheets ensure long-term security. Thanks to their very good cold bending behavior and their high thermal stability, these can withstand the highest loads - reliably even after decades. If the first layer is laid on a temperature-sensitive sub-surface such as EPS insulation boards, heat-sealing is out of the question: cold self-adhesive sealing sheets are the best solution here. As the top layer, the sealing top layer must defy wind and weather. Their quality is decisive for the life of the roof. Good bitumen products are resistant to aging and far exceed the DIN requirements. If fire protection requirements do not permit the use of the burner, cold self-adhesive strips are suitable. A root-resistant special bitumen welding membrane is the right choice for green roofs. An alternative to sealing with bitumen sheeting is provided by v. a. In lightweight roof constructions, plastic roofing membranes are used. In particular, FPO sealing membranes are recommended due to their high quality, durability and ease of installation.

Material selection
The service life of a flat roof depends crucially on the materials used. Unfortunately, the applicable technical rules only define a standard here. Sustainably built flat roofs with an expected service life of more than 30 years, however, require the use of high-quality waterproofing membranes, the performance values ​​of which are well above the requirements of the standard. However, these often fall victim to the cost situation. The result is renovations after a relatively short time. A test in which a 20 year old roof was opened showed that the sealing function of the bitumen membrane Baukubit K5K from Bauder was fully preserved and exceeded the performance data of today's standard membranes.

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