In contrast to timber stud or timber skeleton construction, solid timber construction refers to full-surface and load-bearing wall, roof or ceiling elements made of solid timber components.
The weather and heat protection of these exterior walls can be provided by various façade systems, such as wooden formwork, external thermal insulation composite systems (ETICS) or rear-ventilated façades (VHF).
Image: Sketch of block construction, multi-layer standing (standing and toothed planks) - bauwion
Image: Sketch of dowel timber construction (dowelled multi-layer elements) - bauwion
Image: Sketch of cross-laminated timber construction (glued multi-layer elements) - bauwion
With the appropriate type and thickness of insulation, solid timber buildings can also be erected as highly thermally insulated buildings. Solid wood components show a high specific heat capacity, so that they show very good properties in terms of summer thermal insulation and sound insulation. A high degree of prefabrication allows for very fast on-site assembly and, due to the dry finishing method, rapid completion overall. When choosing the right manufacturer or supplier, the so-called "RAL Quality Mark for Timber House Construction" can be an important indication of ensuring high quality in production and execution. These farms are independently and regularly inspected by means of internal and external monitoring.
Solid wood construction is not regulated by standards. The building authority approvals and the manufacturer's information are decisive in the planning, and the timber construction standards listed below can only be applied in part as a basis. The static design is also bound to the specifications of the manufacturers. For this reason, architects and planners are supervised and advised by the manufacturers, and workshop drawings are then created from the planners' execution plans by the company's own specialist engineers.
: The surface quality is sorted in accordance with DIN EN 13017-1. A distinction is made between two sortings. For non-visible building elements, top layers are suitable according to C-grading according to EN 13017-1 and are designated NSi . For visible areas, the sorting AB labeled Si is suitable.
Ecology: Compared to other construction methods, the production and processing of solid wood components requires very little energy. As a renewable raw material, wood is CO2-neutral, so that solid wood construction meets high ecological standards. However, the implementation of the basic ecological idea also includes the consistent continuation of the claim in all other components of the building. In this sense, exterior wall insulation, for example, is often carried out with soft wood fibre boards. Untreated solid wood walls can be disposed of and reused at the end of their service life without hesitation.
Measurement systems: In contrast to stud or skeleton buildings, solid wood buildings are not subject to a grid. Only the manufacturer-specific maximum dimensions must be observed. This allows completely free floor plans and facades to be designed.
Interior fittings: Indoors, walls and ceilings can be covered with cladding such as plasterboard. These can be applied with a substructure, e.g. if installation levels are to be constructed. In the case of dowel wood and cross-laminated timber walls, the inside can also be left uncovered.
Thermal insulation: Wood has a thermal conductivity λ of approx. 0.10 to 0.17 W/mK and thus has a medium thermal insulation effect. According to today's standards, however, additional insulation is applied to meet the thermal insulation requirements. Asa rule, external external thermal insulation composite systems (ETICS) or rear-ventilated facades (VHF) are used.
Example: A wall structure with an external insulation of 20 cm soft wood fibre boards on 10 cm cross-laminated timber wall leads to a u-value of 0.17 W/m²K.
Summer thermal insulation: Solid wood has a high specific heat capacity of c = 2100 J/kgK. This means that solid wood walls have an inert temperature behavior, which contributes to a large phase shift. This value is responsible for the fact that solid wood buildings have good thermal insulation in summer.
Fire protection: Although wood is a combustible building material, solid and large-scale wooden components burn very slowly. The so-called burning speed is decisive for this. This is low for solid wood walls, so that under standard conditions about 20 mm of the wall cross-section burns off in 30 minutes. The remaining cross-section remains fully load-bearing. Wood also offers the advantage that the heat is poorly transmitted due to the relatively high thermal conductivity coefficient, which means that the temperature on the side of the component facing away from the fire rises only insignificantly. By increasing the wall thickness, the fire resistance duration can be increased to 60 to 90 minutes. Alternatively, the fire resistance can also be increased by refractory planking such as plasterboard or cement fibreboard. The fire protection certificate must be carried out in accordance with DIN 4102-22 or DIN EN 1995-1-2, taking into account the burn rates.
Sound insulation: Solid wood walls offer sufficient sound insulation properties within an apartment. For increased demands, such as partition walls between two apartments, double- or multi-layer wall systems are used.
The impact sound insulation required by DIN 4109 can also be guaranteed in the solidly built wooden house. For this purpose, the ceilings are usually also made of solid wood elements. To decouple the sound input, floating screeds are used on impact sound insulation with low dynamic stiffness. Even the increased sound insulation according to DIN 4109, Supplement 2 can be achieved by additional measures, so that apartment buildings in solid wood construction are also possible.
Wind and airtightness: The wall systems described above must be designed so tightly both in the surface and at the transitions that an external wind seal and an internal air seal can be dispensed with by additional layers such as foils.
Building physics: Depending on thickness and bonding, solid wood walls have a water vapour diffusion resistance factor μ between 30 and 80. This creates a diffusion-inhibiting effect with standard wall thicknesses, so that no vapour barrier is necessary on the inside of a diffusion-open structure outside the wooden wall. Any interior paneling can be omitted, so that the wood look can remain visible inside. Airtightness is guaranteed in the area by the wooden walls. Compression bands must be inserted at joints and corner joints.
Wood protection: Wood-destroying fungi and insect infestation are not to be expected with a wood moisture content of less than 20%. For this reason, wooden components that remain permanently below 20% wood moisture even when installed are to be assigned to use class GK 0 or GK 1. The use classes GK 0 and GK 1 include components that are not weathered, are not exposed to humidification and are not in contact with soil or water. This usually applies to all wall and ceiling components of a solid wood building, so they do not need to be treated against fungal or insect infestation. In addition, there is no restriction on the types of wood in this case. Only from use class 2 onwards can only certain woods be used. The conditions and distinctions of the wood-susceptible fungal species are described in DIN EN 335-1: 2006-10, Annex A.
Statics: The proof of stability must be prepared on the basis of the respective manufacturer-dependent general building authority approval. In this respect, it is advisable to determine the desired solid wood system before creating the stability certificate.
Base formation: All wooden components must maintain a distance of at least 30 cm from the top of the ground. This plinth height can be reduced to 15 cm if either a gravel strip with a grain size of at least 16/32 is made along the wall, or if there is a draining surface with a slope of at least 2%. The plinth height can be reduced to 5 cm if an additional sealing measure is carried out in accordance with DIN 18195, Part 4.
: Solid wood walls are prefabricated at the factory and can be assembled on the construction site in a short time. However, the time planning must take into account the preparatory elements that the plant needs for the work drawings, including coordination, approval and production.
Wood moisture: Wooden components should always be installed with about the wood moisture content that can be expected in the finished state. During transport and storage and during installation, care must be taken to ensure that the wooden components remain dry and are not moistened by soil moisture or precipitation. In this way, swelling and shrinkage can be reduced to a minimum. If a temporary increase in moisture cannot be prevented, e.g. when installing wet screeds, the desired moisture content must be restored by intensive ventilation, heating and technical drying.
Waterproofing: Before the wooden elements are erected on a floor slab or in the transition to other concrete components, a separating layer must be applied against rising damp. This can be, for example, sanded bitumen cardboard.
Tightness: To prove the required airtightness, a "blower door test" should be carried out after completion of the building envelope.
DIN EN 1995-1-1, Eurocode 5: Design and construction of timber structures - Part 1-1: General - General rules and regulations for building construction
DIN EN 13017-1, Solid wood panels - Classification according to the appearance of the surface - Part 1: Softwood; German version EN 13017-1: 2000
DIN EN 13017, Solid wood panels - Classification according to the appearance of the surface - Part 2: Hardwood
DIN EN 460, Durability of wood and wood products - Natural durability of solid wood - Guide to the requirements for the durability of wood for use in the hazard classes
DIN EN 594, Timber structures - Test methods - Wall panel load-bearing capacity and rigidity of walls in timber panel construction
DIN EN 599-1, Durability of wood and wood products - Effectiveness of wood preservatives as determined by biological tests - Part 1: Specification according to the use class
► Block Construction Directive - Technical Principles and Rule Executions for Block Construction, published by the German Solid Wood and Log House Association e.V.
► Holzhauskonzepte Hrsg. Fachagentur für Nachwachsende Rohstoffe►
Informationsdienst Holz News and publications on the subject of timber construction
Source: bauwion
