Holzhybrid_the future of construction | In practice

Timber hybrid – the future of construction?

One third of the world’s harmful emissions come from the construction industry. This fact puts pressure on the real estate sector to look for ways to cut its carbon footprint. Timber hybrid is known for generating fewer harmful emissions than conventional solid construction. This is because timber hybrid construction involves a mix of materials, where timber is usually combined with concrete or reinforced concrete in structural components. Here are some interesting facts about timber hybrid construction.

People have been building with timber for millennia. Over the last century, however, timber has been virtually ignored in multi-storey or high-rise construction and is not used at all for offices or administrative properties. To date, timber has rarely been used as the predominant material in this class of building.

The staple raw material in almost all new construction projects is concrete. Over 4.6 billion tonnes of cement are produced around the world each year for its manufacture. This requires large amounts of energy, which means that around 2.8 billion tonnes of CO₂ are released into the atmosphere every year. Yet concrete is cheap as well as tremendously stable and durable, and can be easily and quickly put to work. In the past 80 years, it has been regarded as virtually the only option.

The figure shows the structure of timber hybrid construction:
Ground slab and core in reinforced concrete, wooden supports and wooden beams, facade elements in timber construction, timber hybrid ceiling elements of a reinforced concrete ceiling in reduced strengths and wooden beams

Source: Calculated from data published by the Federal Statistical Office of Germany 2018

However, the legal requirements for more climate action in the real estate industry are increasing. There is avid interest in timber hybrid construction and political backing for sustainable construction projects. Timber hybrid construction combines the strengths of timber and concrete and is increasingly sought after in the real estate industry as a product that cuts carbon emissions. This construction method has also been used for large and high-rise buildings for some time now. Well-known examples include the HoHo high-rise in Vienna, Mjøstårnet in Brumunddal (Norway), EDGE Suedkreuz Berlin and Skaio in Heilbronn.

Properties of concrete, reinforced concrete and timber

Concrete:
Artificially produced from sand or gravel and chemical additives, large amounts of CO₂ emitted during production, approx. 20 % of the original CO₂ emissions are absorbed from the atmosphere through carbonation over the life of the building.
Reinforced concrete:
Manufactured in the same way as concrete, but with steel reinforcement, has a high level of compression and tensile strength. Production consumes a lot of resources and energy.
Timber:
Natural building material, absorbs CO₂, has a high level of compression and bending strength. Composite construction is used in practice, which reduces the proportion of concrete and steel and allows greater use of renewable raw materials.

Fascination with timber

Timber is a fascinating construction material. It stores carbon dioxide and can replace mineral building materials. As a renewable raw material, it therefore plays a doubly positive role in the carbon footprint of construction. The material also has a high tensile strength and a comparatively low weight. Furthermore, building with timber keeps construction times short due to serial and modular construction with a high degree of prefabrication, which can lead to a shorter construction process.

So how can it be that timber is being talked about so much but it is a long way off being used on every construction site? There are various answers to this. According to a survey, architects are open to the timber hybrid construction method. They claim their biggest obstacle is little knowledge of this topic among builders, while the latter – equally legitimately – point to a lack of experience among architects, planners and contractors. Finally, the number of large projects is still limited. A closer look at this subject reveals even more opportunities and risks:

Fire safety requirements
The combination of timber and non-combustible materials as well as a separation between the storeys make it possible to achieve just as good fire protection with timber hybrid construction as with the solid construction method. These requirements may be stricter depending on the national or regional government authority.
Fewer undesirable side effects of construction
Shorter construction times and serial and modular construction can significantly shorten building times and therefore also reduce the impact of dust and noise emissions on the neighbourhood. Costs can also be reduced in principle. The relocation of work from the construction site to the production shop floor, which is becoming standard for many construction methods thanks to more digitalisation, is already well-established in timber construction. Widespread application is not yet possible, however, due to a lack of both experience among the planners and the qualified personnel carrying out timber construction and capacities in the corresponding plants. This can cause friction losses or even longer planning times.
Can it help protect the climate?
Yes. Timber hybrid construction can save considerable amounts of CO₂ during construction, demonstrably cutting up to 80 % of harmful emissions in some cases. Nevertheless, this method is probably not a solution for mass construction projects and cannot completely replace concrete, because the availability of sustainably grown timber is not guaranteed when demand is very high. If the timber needs to be transported over long distances, this negatively impacts the carbon footprint.

Another building block in the mixture to cement climate protection

Attitudes are shifting within the construction industry and this much is certain: timber is a flexible, high-quality and popular building material that will grow in importance in all real estate classes. However, the timber shortage in 2021 has also taught us that this building material is not always available in unlimited supply. And timber is just as affected by volatile pricing as all other raw materials, which in turn have a direct influence on construction costs. Timber hybrid is not a cure-all, but represents another attractive option on the path to a more sustainable real estate industry.

at a glance Sustainability