Rear-ventilated façades (VHF), synonymous with "exterior wall cladding, rear-ventilated", represent a high-quality and extremely versatile option for façade design.
What they all have in common is the structure of an insulating layer, substructure/rear ventilation and the actual façade cladding.
The increased space required by a VHF, for example compared to a façade with an external thermal insulation composite system (ETICS), should be taken into account at an early stage of planning.
In addition to the decision for the final surface material of the VHF (see table), and the associated individual design possibilities, the appearance is decisively determined by the determination of shape/format (e.g. panels, panels, panels, rhombuses, squares – each changing evenly or regularly/irregularly), colour, surface (e.g. structured, pre-patinated, milling/perforation, sanded, graffiti protection), joint (e.g. staggered joints, cross-joints), fastening (visible/invisible) and laying pattern (e.g. open/closed joints, inverted).
System: Façade cladding, substructure and insulation must be approved for installation as part of a rear-ventilated façade (VHF). The compatibility and compatibility of the various components with each other must be checked.
Static verification: The static verification of the rear-ventilated façade must take into account the load cases of dead load and wind suction/pressure. The resistance to wind loads must be proven in accordance with DIN 1055-4. Further loads, e.g. from components for advertising or window systems, must not be introduced into the VHF including the substructure.
Substrate: The static verification determines the number of required attachment points, also depending on the material of the substrate. In new buildings, an exterior wall made of reinforced concrete is usually chosen as the substrate, but in principle, VHF facades can also be erected in front of load-bearing brick exterior walls, e.g. as part of an energy-efficient renovation.
Substructure: The substructure is made of wood or aluminium, also as a combination of both materials. In any case, three-dimensional adjustability is required in order to be able to compensate for unevenness of the substrate, e.g. due to construction tolerances or minor offsets. The substructure consists of the following elements:
Lightning protection: In combination with an aluminium substructure, additional lightning rods in the façade area can be omitted. This saves costs and avoids the aesthetic impairment of the façade by visible lightning rod systems.
Insulation layer: The technical building regulations introduced and DIN 18351 (VOB C) No. 3.5 result in the use of non-combustible insulation in the form of mineral wool insulation boards. The U-value of the outer wall, which can be achieved in comparison with the project-specific EnEV verification, together with the selected thermal conductivity group of the insulation (usually thermal conductivity group 032 or 035), influences the thickness of the insulation and thus also significantly the total depth of the VHF. There are insulation systems with or without fleece lamination, but they all have a hydrophobic coating in common. This prevents rain and even long-lasting fog moisture from penetrating the insulation layer and the insulation retains its heat-insulating function to its full extent. For façade constructions with large joints (>5 mm), the use of dark fleece-laminated insulation materials is recommended for visual reasons.
Renovation of existing facades: Existing buildings can generally be renovated well with a VHF system, the design possibilities are very large, and in terms of energy and appearance, the renovated facades can come very close to a new building. The additional space required for the VHF façade, including the insulation and rear ventilation level, must be taken into account. In the case of existing façades, special attention must also be paid to the static quality of the existing outer wall, as the punctual attachment points must absorb the high load from dead weight and wind pressure/suction. Because the load-bearing capacity of the subsoil is usually unknown, this is usually determined by pull-out tests on the structure, and then the structural engineer determines which type of fastening (e.g. dowels, injection anchors) and what distances of the substructure are required. It cannot be assumed that every existing exterior wall construction has a sufficient load-bearing capacity, so the pull-out tests should be carried out at an early stage of the planning if there are doubts in this regard. This particularly affects masonry walls, and especially VHF systems with a high dead weight, e.g. with stone façade panels.
Fire protection: The state building codes contain stipulations on fire protection requirements for exterior walls and façades, in each case depending on the building class and, where applicable, supplemented by other regulations such as a garage ordinance or a special building regulation.
[...] ... read more on bauwion - BauWissenOnline
Weather conditions: In the event of snow, ice, strong winds and temperatures below 5°C during bonding work, additional suitable measures may be required, which the executing company must take in coordination with the client and for which it is entitled to a separate remuneration in accordance with DIN 18351 (VOB C) No. 3.1.5.
Substrate: The substrate must meet the static requirements in particular (see above).
Scaffolding position: Insufficient consideration of the scaffolding position can lead to supplements and additional costs in the construction of rear-ventilated façades. The maximum permissible distance between scaffolding (catch layer) and structure in accordance with DIN 4420-1 is 0.30 m. As a rule, this space is not sufficient to construct the shell with the same scaffolding position without additional measures, as well as to assemble the rear-ventilated façade including insulation. It is therefore advisable to take into account the later space required to assemble the entire VHF when erecting the scaffolding during the shell construction work. This requires either the installation of booms/scaffolding extensions in each catch position or the installation of additional internal side protection, consisting of railing spar and intermediate spar(s). This should be taken into account accordingly when tendering the scaffolding work.
Note: DIN 4108-1 (Thermal insulation in building construction; Sizes and units) has been withdrawn and replaced by DIN EN ISO 7345
DIN 18351 (VOB C), General Technical Terms and Conditions of Contract for Construction Services (ATV) – Rear-ventilated facades
DIN 18516-1, Exterior wall cladding, rear-ventilated - Part 1: Requirements, test principles
DIN 18516-3, Exterior wall cladding, rear-ventilated - Part 3: Natural stone; Requirements, design
DIN 18516-4, exterior wall cladding, rear-ventilated - Part 4: Toughened safety glass; Requirements, design, testing
DIN 18516-5, Exterior wall cladding, rear-ventilated - Part 5: Cast stone; Requirements, Design
Leaflet Proof of the suitability of cast stone according to DIN 18516-5, Prof. Dr. Alfred Stein, Editor: Bundesfachgruppe Betonwerkstein, Fertigteile, Terrazzo und Naturstein im Zentralverband des Deutschen Baugewerbes
DIN EN 438-1, Decorative high-pressure laminate boards (HPL) - Boards based on hardenable resins (laminates) - Part 1: Introduction and general information
DIN EN 14411, Ceramic tiles and slabs - Definitions, classification, properties, conformity assessment and marking
DIN EN ISO 7345, Thermal insulation - Physical quantities and definitions
DIN EN ISO 11833-1, Plastics - Plasticizer-free polyvinyl chloride sheets - Types, dimensions and properties - Part 1: Sheets with a thickness of at least 1 mm
Source: bauwion
