Understanding Timber Constructions

In order to understand the different timber construction types a short overview of the common construction methods in Europe is given in this section. This summary is written on the basis of the work “Potentials of building with wood”, a compiled work from the german Federal Environmental Agency.

Timber Panel Construction

The wooden panel construction is also known as timber frame construction. It is a composite construction consisting of ribs and planking on one or both sides. The planking has a static effect (in contrast to cladding). The stiffening of such wooden panel constructions is done by the wooden panels themselves, which are used as wall and ceiling panels and therefore carry not only vertical but also horizontal loads. 

Depending on the place of use, the elements are referred to as wall, ceiling or roof panels. 

For columns, frames and sills, solid structural timber is usually used, less frequently solid timber, and even less frequently glued laminated timber. Thus, these components are predominantly made of softwood, although the use of hardwood is possible. 

Wood-based panels are used as cladding. Both laminated veneer lumber and plywood as well as OSB panels and, in part, particleboard and fiberboard are used. 

Typical examples are the so-called prefabricated houses: single-family and multi-family houses from various prefabricated timber house suppliers. 

The advantages of the timber panel construction methods lie in the prefabrication and the resulting rapid assembly. For prefabricated houses, for example, wall, ceiling and, where applicable, roof panels are usually completely prefabricated – including insulation, waterproofing, plastering, windows and pre-installation – and delivered to the construction site. At the construction site, the panels then only have to be lifted into place

Figure 1:  Schematic structure of a wooden panel

Timber Frame Construction

Timber frame structures (sometimes also referred to as skeleton construction)  are column/beam structures whose load-bearing structure – the columns as vertical components and the beams as horizontal components – is created independently of partition walls, so that a high degree of flexibility is achieved in terms of finishing – analogous, for example, reinforced concrete skeleton construction. 

Because of the labor-intensive junctions and the desired flexibility, a column and beam grid with the greatest possible spacing is generally preferred. 

Stiffening is provided by the timber frame itself or by additional stiffening systems. As a rule, horizontal stiffening is realized by stiffening or floor slabs, while vertical stiffening is realized by stiffening, frames, restrained columns, wall plates or even solid reinforced concrete cores.

Columns and beams are usually made of solid structural timber or glulam. Thus, these components are predominantly made of softwood. However, the use of hardwood is possible. 

Figure 2: Schematic diagram of a timber frame building

Solid Timber Construction

Solid wood construction refers to a timber construction method with solid, uninterrupted (as opposed to spaced beams, columns, ribs, etc.) wall, ceiling and roof elements.

The individual elements are usually designed as board stack elements or cross laminated timber elements. Thus, these components consist almost exclusively of softwood. The use of hardwood would, however, be possible for cross-laminated timber elements and is fundamentally conceivable for stacked board elements.  However, approvals for such elements do not yet exist. 

Laminated veneer elements can also be used, which would make the use of hardwood more feasible. However, in a strict interpretation of the term solid wood construction, such elements would not be considered.

Wood-concrete composite structures represent a special area of solid wood construction when they are created with panel-shaped wood elements. In the meantime, they are used so frequently that they are regarded as an independent construction method. They are therefore listed separately below.

Figure 3: Solid wood construction with board stack ceiling, beams and cross laminated timber walls

Wood Hybrid Construction

Wood-concrete composite structures, recently also increasingly referred to as wood hybrid structures, are ceiling structures consisting of a composite of an upper reinforced concrete plate and lower wooden beams or solid wood ceiling elements. 

Wood and reinforced concrete are connected by special shear connectors, cams, cervicals or even inclined bolts and participate in the load transfer on a percentage basis, taking into account their stiffnesses and the mean stiffness of the connection.

The panel-shaped wooden components of the wood-concrete composite structures are usually designed as board stack elements, more rarely as solid wood panels or as cross laminated timber panels. Thus, they consist almost exclusively of softwood. Bar-shaped wooden components – wooden beams – are usually made of solid structural timber, more rarely of laminated timber. They consist almost exclusively of softwood. The use of hardwood would be conceivable in principle, but the regulations governing fasteners must be observed.

Figure 4: Principle of a wood-concrete composite floor

Source: Wolf, T., Untergutsch, A., Wensing, C., Mittelbach, H., Lu-Pagenkopf, F., Kellenberger, D., Kubowitz, P. (2020). Potenziale von Bauen mit Holz – Erweiterung der Datengrundlage zur Verfügbarkeit von Holz als Baustoff zum Einsatz im Holzbau sowie vergleichende Ökobilanzierung von Häusern in Massiv- und Holzbauweise, 58-64. Umweltbundesamt 

Direct Link: http://www.umweltbundesamt.de/publikationen