Driving wooden apartment buildings forward for almost 30 years

Text: Markku Karjalainen, Rakennusopin professori, TkT, Arkkitehti, Tampereen yliopisto, arkkitehtuurin yksikkö Photo: Mika Huisman, Tais Griguol, Oulun Puustudio

Read the article in Finnish: Puukerrostaloja puskemassa lähes 30 vuotta

I first ran into the development of wooden apartment buildings in Finland in 1994. The occasion was a seminar on the topic, which we arranged at the Oulu City Library with Pertti Hämäläinen, the managing director of Puuinformaatio ry at the time, and the architecture department at the University of Oulu. As a young teacher of construction, I was very sceptical about wooden multi-storeys. Around that time, Finland’s first wooden apartment buildings were going up in Viikki, Helsinki and at the 1996 Housing Fair in Ylöjärvi.

Myllypuro wooden urban village in Helsinki.

We began to design Oulu’s first wooden apartment building, Kiinteistö Oy Puukotka, under the guidance of Professor Jouni Koiso-Kanttila. The starting point was a student idea competition in spring 1995. Puustudio (the Wood Studio) was set up in the architecture department of the University of Oulu, and the students who succeeded in the idea competition joined in to design the site. Puukotka was finished in March 1997.

From individual buildings to modern wooden cities 1997–2011

After Kiinteistö Oy Puukotka, we at Puustudio decided to petition the City of Oulu for a more extensive test construction area for wooden apartment buildings. They gave us Puu-Linnanmaa, an area for wooden construction opposite the main campus of the University of Oulu. Puu-Linnanmaa was finished in 2003 and received the national Wood Prize. The nationwide Modern wooden town project was launched around the same time and lasted from 1997 to 2011. This 15 year project sought to create a number of presentable residential wooden milieus to serve as models for the future alongside Puu-Linnanmaa. The main supporters of the project included the Finnish Funding Agency for Technology and Innovation (called Tekes at the time, now called Business Finland), the Finnish Ministry of the Environment, Puuinfo Oy, the Finnish Forest Industries Federation (Metsäteollisuus ry), Suomen Puututkimus Oy , and from 1999 onwards even the Ministry of Agriculture and Forestry of Finland with funding from the Puutuotealan osaamiskeskus (the Wood Products Centre of Expertise), which was appointed by the Finnish government and operated between 1999 and 2006.

A number of seminars and architecture competitions were organised during the project to facilitate new wooden environment projects. Turku’s Linnanfältti, Helsinki’s Myllypuro wooden urban village and Tampere’s Vuores wooden complexes are the best known of the project’s offspring. Various sites received attention in the project’s literature, including Moderni puukaupunki – puu ja arkkitehtuuri (Modern wooden city – wood and architecture) and Kotina puinen kaupunkikylä (The wooden urban village as a home). The wooden apartment building construction textbook was also updated in 2013.

Linnanfältti wooden apartment blocks in Turku.

National wooden construction programs had ambitious goals

Government programmes have set quantitative targets for wooden apartment building construction over the years, such as making up 10% of the multi-storey construction market. This goal has not been achieved. Between January 1995 and September 2022, 132 residential buildings with more than 2 storeys were built in Finland, offering a total of 4,208 apartments. Meanwhile, the number of new apartments constructed annually in all multi-storey buildings has been 30,000–35,000 for the last five years. The number of wooden apartment buildings is slowly increasing thanks to cities and municipalities across Finland including all-wood multi-storey construction areas in their municipal plans.

The Finnish Ministry of the Environment commissioned a project survey in June 2022. It determined that wooden multi-storey buildings with approximately 6,000 apartments will be completed in the next few years, and that there are also potentially another 8,000 apartments in the pipeline. I’m not so concerned about the actual numbers myself. I think the most important thing is that these projects succeed and that their residents are happy with the results.

A variety of frame systems are available for wooden apartment buildings

Wooden apartment buildings have been constructed with a variety of frame systems in Finland. The first mostly used the American platform framing system. This type of construction is based on layered skeleton framing, typically using prefabricated readymade elements (small or large elements).

The use of large elements in wooden multi-storey buildings is now very common. Glulam has also been used in skeleton framing. Different mixed framing systems are also possible. Wood facades are commonly used in Finnish wooden multi-storey buildings, but other facade solutions are also possible. Early on, I was of the opinion that if you’re going to build with a wooden frame, then you should go the extra mile and use wooden facades. Over the years, I have softened my stance. These days, I prefer to talk more about using wood in construction than merely about wood construction.

CLT and LVL have dominated as materials in wooden apartment buildings in Finland over the last ten years, and they are particularly popular in tall wooden apartment buildings as large or volumetric elements. This is because CLT and LVL have easy-touse joints, they stiffen the building frame, don’t settle, and are airtight.

Wooden volumetric element construction became more popular in Finland after 2013. However, this approach has lost credibility in the past few years as volumetric element manufacturers and builders have run into economic difficulties, which has also reduced the available supply. The constant fluctuations of lumber prices have also not favoured CLT. Currently, planar and volumetric elements appear to be once again regaining their popularity in wooden apartment buildings.

Feedback from residents has been positive

As I did research for my own dissertation at the end of the 1990s, I conducted a fairly comprehensive survey of residents in Finland’s first wooden apartment buildings with more than 2 storeys. This resident survey covered seven wooden apartment building sites with a total of 20 buildings and 242 apartments. The Finnish Ministry of the Environment commissioned a new extensive survey of residents and builders of wooden apartment buildings in 2017. Conducted by Tampere University’s Faculty of the Built Environment (Architecture), the survey included nine of the newest wooden apartment building sites from different parts of Finland with a total of 17 buildings and 585 apartments. The most recent resident survey was conducted in May 2022. It covered nine wooden apartment building sites in Tampere, with a total of 15 buildings and 486 apartments.

All the resident surveys found that developers and residents had a positive view of wooden apartment buildings and hoped that the amount of wood construction and use of wood would increase in Finland. Resident surveys indicate that respondents generally consider wooden apartment buildings to be cozy, comfortable, and functional as well as having good indoor air, wonderful architecture, and good sound insulation and fire safety. The resident surveys do call for extra attention to be paid to impact sound insulation in the light intermediate floors of these buildings. Residents want more wood to be used, particularly in the interior cladding for stairwells, balconies, and apartments. Modern-day residents are increasingly aware of environmental issues. There has been no need for special repairs in wooden apartment buildings. According to Mika Airaksela of Rakennusliike Reposen, there have actually been fewer repairs under warranties in wooden apartment buildings than in similar concrete buildings.

Increasing training and cooperation in wood construction

To meet the demand for large-scale industrial wood construction, we need to update wood construction training and to ensure we keep this training up-to-date at all levels in Finland. Architects in particular are now very interested in wood construction. Structural designers need to learn a lot about Eurocodes, CE markings, and the ever-changing energy regulations and resource efficiency targets. This means that guidelines and design tools and programs need to be easy to use and logical. Puuinfo Oy has done a great job for a long time on this issue. Mikko Viljakainen, who worked as CEO at Puuinfo between 2010 and summer of 2020, deserves special thanks for producing professional material.

Tampere University has seized the opportunity to address challenges in developing, researching, and teaching industrial wood construction in Finland. Examples of cooperation between the university’s civil engineering and architectural units include: Graduate School of Industrial Wood Construction (2021–2026), Wood expertise for Pirkanmaa – a European Social Fund Plus funded continuing education project (2021–2022) and tPUUr – the digital learning material for industrial wood construction project (2021–2022).

Markku Karjalainen works as a Associate professor of construction theory at the University of Tampere’s architecture unit. He completed his doctoral dissertation in 2002 with the topic: “Finnish wooden apartment building – at the forefront of the development of wooden construction”.