FROM A CLIMATE point of view, renewable wood is the best material choice. Industrial construction in wood is also an efficient way of building apartment blocks, and so interest is steadily growing. With minimal waste of resources, large parts of the building, in some cases up to 80 percent, can be made ahead of time in a factory and then easily assembled on the construction site.
“It’s an economical way of building. A high degree of prefabrication also speeds up the process,” explains Mikael Lindberg, CEO of Martinsons Byggsystem.
In addition, the low weight cuts down on transport costs and environmental impact. Prefabrication can be taken many steps further than with traditional materials. A modern timber frame, usually made from spruce, has practically all the structural components already in place.
“We’ve taken a large step away from traditional construction on site. If there is any sawing, drilling and milling to be done, it should be done in the factory,” says Johan Åhlén, CEO of Moelven Töreboda.
Among today’s producers of large wooden buildings, box units are the solution most commonly used. Modules of a whole room or parts of a room can be delivered fully equipped and then easily assembled on location. For more irregular designs and more open layouts, surface units and post and beam systems are a better solution. Compared with box units, this involves more assembly on site, but the components are still largely produced under factory conditions.
LIGHT FRAME TECHNOLOGY involves the modules being put together in the factory and then delivered to the construction site ready cut, sorted and labelled. No sawing into shape and no waste on site, everything is ready for assembly. The low weight of the wood makes for easier lifting, causing fewer strain injuries. With light frame technology, it is easier to increase the housing density in major cities, either by adding extra storeys to existing buildings or by developing land that was previously judged not to be viable for building. Cross laminated timber (CLT) and post and beam systems using glulam, or a combination of the two, are ideal for taller buildings or structures with larger spans.
“But you can create the same properties in a building, whichever technique you use. To a large extent, it’s a matter of taste. If you want to keep the wood visible indoors, a CLT frame works well as part of the interior. Otherwise, it can make more sense to use a post and beam system in glulam,” says Johan Åhlén.
The USA and Japan are at the forefront when it comes to high-rise buildings in wood. In Europe, Scotland leads the way, with over 30 percent of apartment blocks built in wood, using a high degree of prefabrication. The Scottish government sets clear requirements for sustainable solutions in the construction industry.
Susanne Rudenstam, head of the Swedish Wood Building Council, would like to see similar requirements in Sweden.
“It’s good that Boverket has been tasked with looking at how climate considerations can be incorporated into Swedish building regulations. Setting out the environmental impact of the entire construction process will strengthen the competitiveness of wood no end.”
IF THE PROMISES of increased homebuilding are realised, Sweden will soon face an explosion in construction, with upwards of 50,000 new apartments a year for five years. Tomas Nord, a researcher at Linkoping University with a particular interest in the wood industry, estimates that wood should be able to increase its market share from the current 10 percent to 30–35 percent within 10 years.
However, old habits die hard. There is still an active generation that has never learned to build upwards in wood. Convincing educators to include wood as a natural choice of material is taking time. All sorts of prejudices remain concerning fire, damp, acoustics and stability.
“Countering all these preconceptions requires a great deal of work on our part. It’s an aspect of the sales work that traditional materials don’t have to contend with. But for every project we complete, we help to increase the know-how of developers,” says Johan Åhlén.
He believes in the importance of having project support close to the construction site, with the supplier remaining available throughout the process, particularly now in these early stages of developing a construction system. Susanne Rudenstam also emphasises the importance of disseminating knowledge.
“The key word is collaboration, entering the process at an early stage and getting all the stakeholders to think wood. As industry representatives, we make sure all the facts and calculation data are available when the structural engineers ask for it.”
MARTINSONS BYGGSYSTEM HAS created a concept for wooden buildings in partnership with engineering consultants Tyréns and Murman Arkitekter.
“We sit down with a blank piece of paper and look at the solutions from the beginning, just so the architect doesn’t jump too far ahead before we have to say: ‘Hold on! You have to change the spans and design of the building for our system to work’,” says Mikael Lindberg.
It is exactly this openness that Tomas Nord advocates. Suppliers have to be clear about what it takes to build efficiently.
“Look at the automotive industry. There they have basic platform that underpins the design, but beyond that there are endless opportunities to modify the appearance and functions. By drawing up a model-oriented programme, you can create a stable system, where certain players take responsibility for the models, while others create new solutions based on these models. It’s a good way to move things forward.”
This is not how things work in the construction sector as yet, but Tomas Nord stresses that the conditions are in place to develop in a similar way to the automotive industry, particularly when it comes to industrial construction. The key is to use a product platform to create efficient and standardised processes.
“In order to create economies of scale, it should be possible to copy the module and system supplier concept from the automotive industry.”
3D technology and prefabrication in innovative buildings
We have examined four projects that embrace the opportunities offered by industrial construction in wood. Only the circumstances and methods differ.
AT 14 STOREYS, Treet, the world’s tallest apartment block in wood, stands triumphantly next to the Puddefjord bridge on Damsgårdssundet in Bergen.
“As well as being rooted in the long Norwegian tradition of using wood, Treet also slots into a modern, Scandinavian design tradition with a focus on good materials, solid craftsmanship and smart design,” says chief architect Per Reigstad.
Three types of wooden design have been used, with the structural frame placed on the outside. To make the height possible, the frame is made of glulam and protected by glazed balconies on two sides. Internally, all the shafts are made of CLT.
The apartments are delivered as almost turnkey modules – box units that are stacked on top of each other, four storeys at a time. On floors five and ten, two platforms were built, reinforced with three-metre tall glulam beams, that were anchored in the structural frame.
“The largest modules are 5.4 metres wide. This ensures efficient use of modules in relation to the layout,” comments Per Reigstad.
The whole building was rendered in 3D and digitised from the outset, with a high degree of CNC production. The supplier took part from the earliest planning stage in order to create a building that was tailored to the deliveries and not the other way around.
Clear communication was essential. Per Reigstad puts much of the success down to the open, neutral file format IFC, which allows the exchange of information between CAD programs and other software.
“It has been an exciting and educational process. The collaboration has worked extremely well. Since we’ve needed so many innovative solutions, we’ve had to think across professional boundaries.”
3D TECHNOLOGY ALSO played a major role in creating Preikestolen in beautiful Strand in Norway. The 1,100 square metre hotel came about when Stavanger Tourist Association decided to expand the local services to include a restaurant and more comfortable accommodation. Practically everything above ground is made of wood. With a roof design that reflects the surrounding terrain, the hotel sits comfortably in the landscape.
The system used here is Holz100, which comprises several layers of wooden boards held together with wooden dowels. The building involves a total of 400 surface units. The entire structure of the internal walls, external walls, cladding and roof is made from solid timber.
“We wanted to use this technique for its environmental and aesthetic properties. The robust wooden structures are exposed, harking back to traditional Norwegian architecture,” says Dag Strass of the architectural practice responsible for the building, Helen & Hard.
The main body was designed and modelled in 3D. The specifications for the surface units were drawn up in partnership with an engineering firm. Based on these, the manufacturer created drawings and 3D models of the individual components, which were seen by the architects before they went into production, according to Dag Strass.
“With such great collaboration, we were able to go in and modify some of the components, to resolve structural challenges and to create the characteristic look in the restaurant area.
“Prefabrication gives the architect better control over the results, since the geometry and joints can be checked in 3D beforehand. You aren’t as reliant on the accuracy of the tradesmen and their ability to read drawings,” concludes Dag Strass.
LANDESGARTENSCHAU EXHIBITION HALL in Schwäbisch Gmünd near Stuttgart is an architectural prototype that has come out of the research project ‘Robotics in wood construction’, which the city’s university is running together with various project partners. This is the first building with a main structure comprising prefabricated, robot-produced beech plywood panels, 243 of them to be exact. 12 cubic metres of beech plywood was used to encase a gross volume of 605 cubic metres.
The insulation, roofing and exterior cladding were also digitally prefabricated. All the wooden material was grown, processed and manufactured within a radius of 250 km from the construction site. Assembly took just four weeks.
Three of the university’s institutes – the Institute for Computational Design (ICD), the Institute of Building Structures and Structural Design (ITKE) and the Institute of Engineering Geodesy (IIGS) – jointly developed the innovative lightweight construction system.
The panel system makes up the building’s carcass and its shell. The loads that occur around the edges of the panels are effectively spread through the 7,600 individual finger joints, which ensures the stability of the building, asserts Professor Achim Menges of ICD.
“This new form of construction in wood makes it possible to use only 50 millimetre thick plywood.”
The idea is to show the possibilities of digital architecture, how structural calculations, simulations and manufacturing methods can be used to create resource-efficient wooden structures. The key is to develop a contiguous digital chain throughout the process.
ICD’s structural calculation tool has made it possible to include the material’s properties and manufacturing parameters in the design process. Instead of designing each panel manually, simulation is used to automatically find the right shape. The complex structure would have been impossible without robotics, stresses Achim Menges.
“Compared with conventional prefabrication methods, this manufacturing technique enables much greater precision.”
NEW DIGITAL PRODUCTION METHODS also underpin the innovative Copenhagen company Eentileen (1:1)’s vision to erase the dividing line between the architect and the builder. The idea is to offer a customised construction system. ‘Print out your building’ is the motto. Eentileen offers everything from standard to specialist solutions. Common to all the designs is that they are prefabricated in a factory or on site using a CNC machine. Robots are also being used to an increasing extent. Eentileen’s first digitally produced building, Villa Asserbo, outside Copenhagen, was printed out on a large CNC printer using 820 plywood panels.
The benefit of Eentileen’s prefabricated components is that they are small and flexible. They are produced directly from a 3D design file and can easily be adapted to the design. Maintaining a direct link between design, production and assembly paves the way for high precision and few errors.
The standard segment offers a number of off-the-shelf modular solutions to choose from. The premium segment is able to turn custom projects into a construction kit that is ready to assemble on site, with windows, doors and wall and façade cladding already fitted. Other architects are able to easily create their own solutions.
Eentileen uses wood for the entire structure. Wood fibre insulation tackles issues of damp and warmth, providing a good indoor climate without the need for a moisture barrier, explains Frederik Agdrup.
TEXT Johan Bentzel