Designing With Mass Timber
Key Considerations and Best Practices
Advantages of Mass Timber engineering
There are several aspects that derived the emergence of mass-timber engineering:
- development of more sustainable construction solutions applicable in various building types,
- more efficient production process which includes prefabrication and automation,
- more optimal time frame and building process that save time, money and energy.
Elements used in mass-timber engineering (LVL, CLT, glulam, etc) are easily manufactured in automatized process as prefabricated elements ready to be assembled on site. Fabrication and automation are secure processes which ensure precision to make every element fit exactly its joins in the whole structure. Transport to construction sites in scheduled time responds effectively to the planned construction dynamics. Small number of workers is able to make all the connections and all the work in general and this will make the whole process more cost-effective.
Besides structural mass-timber elements, exterior and interior façade panels can be prefabricated too with all the necessary layers (cladding, air barrier, insulation, steel framing, windows, vapor barrier and internal wall covering) – that create stability of the structure and of course thermal comfort.
Basic design principles and structure types
There are several basic design principles of mass timber buildings:
- Simple form of a prism, which guarantees its stability and ease of the mounting process,
- Foundations, base are made of reinforced concrete, to create fire-proof spaces for mechanical equipment, as well as secure evacuation passages,
- Core and shear wall system as the main tool for resistance to horizontal loads (wind and earthquake),
- Loading paths need to be uniformed in vertical sense through all storeys, which makes the whole structure more load-resistant and stable.
- When columns are not aligned, additional load-transfer beams are need to create proper transfer of forces,
- Shear walls can be made of both concrete and CLT panels, to transfer the lateral loads through CLT floor plates to concrete core.
Regarding seismic safety, mass timber weight is five times smaller than one of concrete, so mass-timber buildings weigh less than those made of steel or concrete and are therefore more resilient to earthquakes. Naturally, local building codes throughout the world define loads allowed for structural elements to be resistant, as well as the number of floors and building types that can be built in mass-timber. These codes are based on local predictions in each seismic zone. In general, steel connectors provide enough safety and strength to the building, and in case an the replacement is necessary, it can be easily done.
Codes also define fire resistance and safety time for mass-timber structural elements, while software predictions testing can check their real performance in case of a fire incident. Gypsum boards as the most common material used as fire-protection covering that enables additional fire-resistant time of structural elements. Otherwise, in case of exposed wood, the char layer needs to be calculated in order to maintain stability of central wooden mass in the element.
Buildings designed and built in mass-timber technology have performances that guarantee good results in sustainability certification processes. Some of the most valuable benefits that serve LEED certification are those in the following categories:
- Location and transportation – mass timber elements don’t pollute the site (land and air during construction), having almost no waste,
- Materials and resources – include environmental product declarations and data on sourcing of raw materials, while prefabricated elements can be suitable for waste management planning (for their possibility to be demounted, recycled or reused),
- Indoor environmental quality – wood provides thermal comfort and air quality in interior space, while all protective coatings must be certified to low or no harmful emissions.
High buildings in mass-timber will continue to show their benefits, and we hope their massive use in near future will confront one of the climate’s worst enemies – urban heat island effect. New researches will surely evaluate and prove the complex improvements this technology offers to use in battle for more sustainable future.
Even regarding circular economy, mass timber buildings offer numerous benefits:
- They don’t create waste nor pollution at the construction site, during the mounting process, use of building nor at its end of use,
- Their elements are mechanically connected which means that they are easily demountable,
- They are fully recyclable in different ways – their elements can be reused in new structures or their wood becomes new resource for various products, saving natural resources that way.
We appreciate the versatility of mass timber structures, and we love to explore its performances in different project types. For several school projects we designed mass timber structures: Emma Hjorth school and Risvollan Barnehage kindergarten, where whole local communities benefited from new buildings, beautiful, healthy and environmentally responsible.
Mass timber is perfect not only for common structures, but also for those designed in parametric design. One such structure we designed for project Armadillo house in USA, currently in progress, where mass timber elements flexibly follow nature – inspired form of small houses.
In the era of retrofit and extension projects, mass timber certainly finds its use. Our project for University of Engineering extension in Belgrade offered mass timber as possibility to build creative spaces and offer new quality both to the interior space and the environment with CLT panels showing their best combined with concrete in a hybrid structure.
The following decades require serious approach to gasses’ emission decrease, and we are sure that mass timber structures will significantly contribute to this global goal.