The wooden roof truss is the most traditional and common roof structure. It can be built entirely by hand, but also from industrially prefabricated building elements. In addition to simple construction timber, wood-based materials with different properties are increasingly being used for production, which differ primarily in terms of durability and dimensional stability. Due to the constantly growing demands on thermal insulation, new support systems have been developed, such as the box girder or the web girder.
Wood is still the most common building material for the construction of roof structures. It is available in sufficient quantities in Central Europe and is considered a sustainable building material that, in addition to simple biodegradation, also has an excellent ecological balance due to its easy processing and low energy consumption during extraction. With suitable constructions and fire-retardant coatings, a high fire resistance of wooden structures can be achieved.
stiffening: Every roof truss made of wooden framework must be braced. One possibility is outcrossing, so-called wind riser bands, made of galvanized steel. However, a roof truss can also be stiffened by disc-like panel material, for example by grooved OSB boards as interior cladding or by sub-roof panels of various materials on the rafters. The exact determination is made by the structural engineer.
Insulation: When it comes to the location of the insulation of a roof truss, a distinction is made between on-roof insulation and inter-rafter insulation. With a visible roof truss, the roof construction remains visible. Only above the formwork are the vapour barrier layer and insulation applied (= on-roof insulation). In the case of inter-rafter insulation, the insulation lies between the rafters, underneath which is the vapour barrier layer and the interior cladding, possibly on a substructure as an installation level or to compensate for tolerances. There are also mixed forms, for example, inter-rafter insulation is often combined with on-roof insulation for a better insulating effect.
Exposed roof truss: Especially when planning a visible roof truss, a rafter plan should be drawn up in cooperation with the executing company, in which the exact division of the roof truss is determined, taking into account the partition walls adjacent to the roof truss
.Thermal insulation for double-web girders: For roof structures with double-web girders, flexible insulation or blown-in insulation is particularly suitable for avoiding cavities in the insulation plane. Alternatively, however, double web girders are also offered, which already have integrated web insulation to compensate for the profiled cross-section of the girder.
Prefabricated construction: If the construction process requires the roof to be tightened particularly quickly, entire roof elements can be prefabricated. Here, entire elements are made from inner formwork, rafters and outer formwork, which, depending on size and weight, can also be already insulated.
Wood preservation: In order to ensure the durability of wooden buildings, special attention must be paid to the structural wood preservation. However, this alone is not sufficient for load-bearing components in outdoor areas, where chemical wood preservatives must also be used.
: The wood moisture content of construction sawn timber made of softwood must not exceed 20% during installation. In general, all wooden components must be protected from precipitation and high humidity, e.g. the moisture from plastering and screed work. If too much moisture does occur, it must be eliminated by intensive ventilation, heating or technical drying. If the component moisture nevertheless rises by more than 20% during the construction process, it must be proven that the permissible humidity has been reached again within 3 months and without affecting the entire construction. From a wood moisture content of 20%, there is a risk of fungal infestation
Constructionprocess Exposed roof truss: Especially when installing an exposed roof truss, attention must be paid to the weather. If it is not possible to cover the construction that remains visible in a watertight manner in a timely manner and before upcoming rainfall, it must be temporarily covered and protected with foil. Even after roof waterproofing, care must be taken to avoid excessive moisture in the interior, e.g. through plastering and screed work. After waterproofing, this moisture can no longer be dissipated through the roof and cause moisture damage to the visible wooden components, such as mould growth.
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.
DIN 1052-10 Production and execution of timber structures - Part 10: Supplementary provisions
DIN 4074-1 Sorting of wood according to load-bearing capacity - Part 1: Softwood sawn timber.
DIN 4074-5 Sorting of wood according to load-bearing capacity - Part 5: Hardwood sawn timber.
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 68800-1 Wood Protection in Building Construction - General
DIN 68800-2 Wood Protection - Part 2: Preventive Structural Measures in Building Construction
DIN 68800-3 Wood Protection - Preventive Chemical Wood Protection
DIN 68800-4 Wood protection - Control measures against wood-destroying fungi and insects
DIN 68364 Characteristic values of wood species - Bulk density, modulus of elasticity and strengths
DIN 68365 Sawn timber for carpentry work - Sorting according to appearance - Softwood
DIN EN 336 Structural timber for load-bearing purposes - Dimensions, permissible deviations
DIN EN 338 Structural timber for load-bearing purposes - Strength classes
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 14080 Timber structures - Glued laminated timber - Requirements
DIN EN 14081-1 Timber structures - Structural timber sorted by strength for load-bearing purposes with a rectangular cross-section - Part 1: General requirements
Notes on timber and timber Wood-based materials from: German roofing trade: Regulations published by the Central Association of the German Roofing Trade (ZVDH)
Source: bauwion
