Self-supporting metal roofing is a very durable and mostly maintenance-free type of covering.
Apart from plastic-coated products, metals are recyclable and can be used universally from single-family homes to industrial halls. They are particularly suitable for flat roof pitches and can also be used as wall cladding. Metal roofing is available in many colours and finishes and can also be used on curved or curved roofs. In this way, they leave a great deal of scope for individual architectural designs.
To protect against corrosion and the effects of the weather, some metals develop their own protective layer, the so-called patina. Others are protected with coatings. The planning and execution of metal roofs must be carried out particularly carefully, as all metals are diffusion-tight.
Classification: In the standards and technical rules, self-supporting metal roofing is divided into
Roof pitch for large-format self-supporting metal coverings: The standard roof pitch is 7°. Under certain conditions, it can be undercut to the minimum roof pitch of 3° if additional measures are taken. This can be, for example, the insertion of suitable sealing tapes or sealants according to the details published by the IFBS. In addition, manufacturers also specify the permissible roof pitch for their individual products. For example, roof pitches of up to 1.5° are possible with industrially prefabricated standing seam systems. Due to the complexity of the permissible roof pitches, it is recommended to coordinate the roof pitch with the manufacturer depending on the respective product.
Roof pitch for small-format self-supporting metal roofing: The standard roof pitch is 22°. It can be undercut under certain conditions. Up to 10° below the standard roof pitch, undervoltages or underlays can be carried out in accordance with the ZVDH technical rules. If the standard roof pitch is undercut by more than 10°, at least a rainproof sub-roof must be built, and if the pitch is less than 12°, a waterproof sub-roof must be built. In addition, manufacturers also specify the permissible roof pitch for their individual products. Due to the complexity of the permissible roof pitches, it is recommended to coordinate the roof pitch with the manufacturer depending on the respective product.
Water vapour diffusion: Water vapour diffusion plays a special role in metal roofs of all kinds, as metal roofs are absolutely diffusion-tight to the outside. This means that the moisture that has penetrated the roof structure cannot escape through the metal covering, so that condensation can develop and damage the roof structure if no precautions are taken to dry out moisture that has penetrated, see Warm roof version and Cold roof version.
Design as a warm roof: The design of a metal roof as a warm roof is generally not possible with a conventional vapour barrier (with a fixed Sd value <1,500 m) due to the diffusion-tightness of the metal covering.
The design with an internal vapour barrier is problematic, as even small defects, e.g. due to perforations of the vapour barrier or in the area of connections/penetrations, can quickly lead to moisture damage in the roof structure: the penetrated moisture cannot be dissipated upwards through the diffusion-tight metal roof, but also cannot be dissipated downwards through the vapour barrier.
The use of a humidity-variable vapour barrier with variable vapour diffusion resistance is safer: at low relative humidity in the interior (= winter case) it is strongly diffusion-inhibiting, the penetration of warm moist air into the roof construction is prevented. With high relative humidity in the interior (= summerfall), it is very open to diffusion. Due to the warm outside air and the solar radiation on the roof, the diffusion flow runs through the roof from the outside to the inside, any moisture that may have accumulated in the roof flows to the inside and can dry out inwards through the vapour barrier.
Prefabricated sandwich panels are a special case, in which the inner shell is made of sheet metal, i.e. is designed to be absolutely vapour-tight. The design as a warm roof is thus specified by the product. During execution, care must be taken to ensure that the vapour-tightness of the inner layer is also completely established in the area of panel joints, connections to other components and in the area of penetrations, and that it is not interrupted locally, e.g. by drilling holes through the inner shell.
Cold roof version: The rear-ventilated roof, also known as a cold roof, is a technically safe and durable alternative to a warm roof without rear ventilation for metal roofing. The moist air diffusing to the outside can be safely discharged to the outside at any time in the rear ventilation level. In addition, rear ventilation also improves the summer thermal insulation of the rooms below. One disadvantage is the increased space requirement compared to the warm roof. In accordance with the plumbing rules of the ZVSHK (11/2009), the following guideline values apply as state-of-the-art for rear ventilation:
Separation layer under metal roof covering: The separation layer under the metal covering protects the underlying construction during the construction process, but is also necessary according to the "Technical Rules for Metalwork in the Roofing Trade" of the ZVDH if wood preservatives or glues are used for the cover underlay, which could damage the metal roofing. Information from the manufacturers on the necessity of a separation layer must also be observed.
Separating layer, structured: A structured separating layer, i.e. a separating layer with a drainage layer made of plastic mesh on the top, is particularly helpful for non-rear-ventilated constructions, as unforeseen moisture can dry out between the roof cladding and the substructure in the structural level. Other advantages are the better lubrication of the coulters and the sound-absorbing effect of this separation layer.
Sound insulation: Precipitation on a tin roof is louder than, for example, on a tiled roof. In particular, if rooms in particular need of protection are located directly below, e.g. bedrooms, suitable sound insulation measures should therefore be taken, e.g. by installing heavy insulation materials (wood fibre boards) or structured separation layers.
Metal roofs, corrosion: In the sequence of installed metal components, attention must be paid to the redox series. For example, no other metals should follow after a copper roofing, as the washed out copper particles can lead to corrosion in other metals. In addition, when combining different metals, attention must be paid to contact corrosion. The ZVDH's "Technical Rules for Metalwork in the Roofing Trade" lists the possible combinations of different metals. For example, titanium zinc, aluminium and galvanised steel may not be used in combination with copper. If no other option is possible, separation layers or protective coatings must be planned.
Processing temperature: When processing metal, particular attention must be paid to the outside temperature. With titanium zinc, processing below 10° metal temperature is not possible. If necessary, however, the metal can be preheated with suitable hot air tools. A temperature of ≥5° is also prescribed for gluing work.
Safety: The builder is responsible for safety on his construction site, unless he has appointed an external expert for this purpose. Care must be taken to ensure that the scaffolding is positioned in a sufficiently secure position, including roofer safety protection.
Cutting work: Do not cut coated materials with a cutting disc or flame cutter, as the coating will be destroyed by heat.
Mortar corrosion: Fresh mortar causes mortar corrosion on metal coverings. In the case of corresponding work above sheet metal roofing, suitable protective measures must therefore be taken.
Storage: Profiled panels must not be stored flat, but only in an inclined position on wooden blocks or similar. The individual panels must not be pulled from the stack, but must be lifted. In addition, they should not be stored in stacks for more than 2 weeks.
Refinish paints: If damage occurs to paint coatings, it should be borne in mind that refinish paints change differently under sunlight and weather than the baking paints. Larger repair sites should therefore be avoided.
DIN 18160-5, Flue Systems - Part 5: Equipment for Chimney Sweeping Work - Requirements, Planning and Execution
DIN 18334 VOB Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Carpentry and Timber Construction Work
DIN 18338 VOB Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Roofing and Roof Waterproofing Work
DIN 18339 VOB Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Plumbing Work
DIN EN 501- DIN EN 507 Roofing Products Made of Sheet Metal
GermanRoofing Trade: Regulations, published by the Central Association of the German Roofing Trade (ZVDH)
Guidelines for the Execution of Plumbing Work on Roofs and Facades (Plumbing Rules), published by the Central Association of Sanitation, Heating and Air Conditioning (ZVSHK)
Source: bauwion
