Wooden facades

Facades made of wood are considered ecological and sustainable. In addition to their function as building protection for the façade areas below, they usually also play an important role in façade design. The choice of elongated façade elements in vertical, horizontal or diagonal arrangement, small-scale wooden shingles or large-format panels has a strong influence on the façade effect. Especially in mountainous and low mountain ranges, many buildings are clad with traditional rough-sawn board formwork, some of which have survived for decades without maintenance. The prerequisite for a durable wooden façade is first and foremost a construction method that drains water away from the building quickly and without waterlogging, so that all wooden components can always dry quickly after rainfall.

More about wooden facades

Wooden cladding can be used as a façade for wooden constructions or masonry or reinforced concrete walls. They are mounted on wooden slats and can be rear-ventilated, ventilated or non-rear-ventilated with an air layer:

Notes on planning

Wood preservation, coatings: There are a wide variety of coatings and surface treatments that can protect the wood from the weather (see Lexicon ► Wood façade, surface treatment). It is also possible to choose a natural greying, which allows the wood to build up its own weather protection and maintenance of the surfaces is usually not necessary. Possible decision criteria for the appropriate surface treatment: ecological and health aspects, type of site-related biological hazard as well as significance and desired appearance of the wooden façade. Wooden façades, which can dry out quickly due to their design, do not require chemical protection against fungal infestation and damage from wood-destroying insects is not to be expected. The battens behind the wooden façade also do not require any wood preservatives.

Wood preservation, constructive: Surface treatments can reduce the effects of weather on the wooden façade, but they cannot compensate for structural errors.

Particularly important are suitable detailed solutions for the connection points, such as plinths, roof and window connections, slat or panel joints, corners and penetrations.

DIN 68800-2 shows preventive structural measures for wood protection. These apply primarily to load-bearing timber components, but are also recommended for non-load-bearing components.

The most important construction rules for a permanent wooden façade are:

• the entire construction is carried out in such a way that water is drained away (avoid standing water) and it is always possible to dry the wood when moisture accumulates.
• Edge rounding with a radius ≥ 2.5 mm when the coating is planned to obtain an even layer thickness around the edges.
• Undercutting of the lower edges of ≥ 15° to ensure water drainage from the individual wooden elements.
• Formation of all slat or plate joints with at least 1 cm joint in order to avoid capillary water accumulation. In the case of horizontal end-grain joints, it is better to work with metal covers or covers.
• if possible, roof overhangs that additionally protect the entire façade from weather influences such as rainwater penetration.
• suitable plinth design to avoid damage caused by splashing water (see: Pedestal formations).
• Drainage facilities behind the wooden façade to drain any water that may have penetrated.
• Provision for the possibility of easy replacement of individual elements exposed to particularly high loads.
• Regular cleaning and maintenance of the façade

Plinth designs: According to DIN 68800-2, the plinth spacing for weather-protected wood can be reduced from 30 cm to 5 cm. This is somewhat more difficult with wooden façades, as they themselves provide extreme weather protection.

Above horizontal weathered surfaces, a splash water area of at least 30 cm is to be assumed, and up to 50 cm for smooth, closed surfaces. All façade timber in this area is contaminated and damaged by splash water. In this area, a plinth should therefore be made of a suitable material, e.g. plaster, metal or fibre cement panels.

In order to minimise the visible plinth height, the terrain in front of the façade can be lowered by the necessary spraying area. The resulting ditch around the building can be bridged either completely or only partially at the entrances with a grid.

In the case of horizontal formwork, wear boards can also be used. The wooden façade can be guided up to approx. 5 cm above the top of the ground if the lower boards in the spraying area can be easily replaced. This is not possible with slabs or vertical boards.

Connections: The careful planning of all connection details of a wooden façade is not only important to avoid defects in rear ventilation or structural wood protection, but also visually the detailed solutions determine the overall appearance of the façade. There are a wide variety of solutions for the formation of interior and exterior corners, plinth and roof connections, window reveals and element joints. As an alternative to the use of metal connection plates or profiles for covering connections and corners, overlaps can also be formed or wooden strips can be used, for example.

Fasteners: The most common fasteners for wooden facades are screws and nails. However, many manufacturers also offer fastening profiles or hooks that enable invisible installation. The fasteners must have a minimum corrosion protection in accordance with DIN EN 1995-1-1. Stainless steel screws and nails are best. Bolted elements can be easily dismantled for renovation work and are therefore particularly recommended on vulnerable façade parts, such as window reveals. In the case of coated wooden facades, visible fasteners should be painted over after installation. The fasteners are also designed in accordance with DIN EN 1995-1-1.

Construction: A distinction is made between four different constructions for wooden facades. The ventilated façade, the ventilated façade, the non-ventilated façade with a standing air layer and the non-ventilated façade without an air layer, the latter being only possible in a few individual cases

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Notes on construction

acceptance: Important points for the acceptance of wooden facades:

• Is the wood quality sufficient?
• Checking the wooden elements for cracks and defects.
• Is the coating defect-free? Especially in the case of film-forming coatings, the smallest defects quickly lead to peeling off of the coating and thus to damage to the wood.
• Are the fixings in order?
• Screws and nails must be flush with the surface, they must not protrude or be sunk too far to prevent damage to the coating.
• Have the detailed solutions been carried out correctly?
• Check the specified joint spacing, overlaps and connections.

Scaffolding position: Insufficient consideration of the scaffolding position can lead to supplements and additional costs in construction. The maximum permissible distance between scaffolding (catch layer) and structure in accordance with DIN 4420-1 is 0.30 m. This space may not be sufficient to create both the shell and the façade with the same scaffolding position without additional measures. It is therefore advisable to take into account the later space required to assemble the wooden façade 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.

Standards and literature

Note: DIN 4108-1 (Thermal insulation in building construction; Sizes and units) has been withdrawn and replaced by DIN EN ISO 7345

DIN 18334 (VOB C), General Technical Terms and Conditions of Contract for Construction Services (ATV) - Carpentry and Timber Construction Work

DIN 18351 (VOB C), General Technical Terms and Conditions of Contract for Construction Services (ATV) – Rear-ventilated facades

DIN EN 13986, Wood-based materials for use in the building industry - Properties, assessment of conformity and marking

DIN 68800-1, Wood protection - Part 1: General

DIN 68800-2, Wood protection - Part 2: Preventive structural measures in building construction

DIN EN ISO 7345, Thermal insulation - Physical quantities and definitions

DIN 68119, Wood shingles

DIN EN 335, Durability of wood and wood products - Classes of use: definitions, application to solid wood and wood products

DIN EN 350-2, durability of wood and wood products - Natural durability of solid wood - Part 2: Guide to the natural durability and impregnability of selected wood species of particular importance in Europe

DIN EN 13986, Wood-based materials for use in the building industry - Properties, assessment of conformity and marking

DIN EN 14519, Interior and exterior cladding made of solid softwood - Profiled wood with tongue and groove

Technical rules of the carpentry trade 01 Exterior wall cladding made of wood and wood-based materials, Publisher: Bund Deutscher Zimmermeister im ZDB, Berlin

Source: bauwion