PuuMera – large-scale residential construction with wood

The main objective of the PuuMera project was to develop an innovative yet profitable approach to build a large scale residential property in timber. This objective was met. Over of a few centuries of new building material development, reinforced concrete became a cost-efficient option, indeed the new norm for building large scale structures. Not considered economically advantageous, wood did not become the material of choice for large scale apartment buildings. Building larger and taller buildings in wood has been something of the past, even though for example fire regulations today are adjusted to, and accommodate construction in wood on a larger scale than before. However, a considerable share of family residential buildings has remained, to a large extent, timber-based. This is true not only in Finland, but also seen in the landscape of many other countries. In this context, the overall objective of the PuuMera project was 1) to build profitably in wood, and to challenge the common paradigm of using reinforced concrete, and 2) to construct a wood-based property that could be defined as a low energy building. Realising these objectives required developing new ways of working. Hence, the PuuMera approach has also integrated co-creation as part of its concept, and has, for example, engaged future residents already in the design phase. The PuuMera concept was developed by the Finnish construction company Reponen and its partners, and the concept has been realised through a series of three wood-based apartment blocks. The apartment building in Vantaa’s Kivistö, completed in the autumn of 2015, utilises innovative laminated timber structure methods, which were developed in a previous project in 2011 in Vierumäki, Heinola. A third PuuMera building, sited in the area of Honkasuo in Helsinki, was completed in 2017. The prefabricated wooden elements are produced indoors in order to ensure desired accuracy and quality of work, and to avoid moisture related problems. The work done at the building site is fast, as the wooden elements and parts arrive at the site ready for assembly. With careful planning and design, as well as the use of new technologies, the fire safety levels may in fact be considered better than with traditional concrete building methods. Fire safety regulations are clearly addressed and accounted for, and automated sprinkler systems installed. For example at the Kivistö site, each apartment has its own high pressure sprinkler system. In terms of life cycle considerations, the PuuMera maintenance and service requirements are on par with concrete buildings. For example, the facades require re-painting every 15 years, after which they are good as new, and do not require condition sampling and laboratory testing. The PuuMera building is built to the passive building standard; therefore ventilation is always kept at a suitable rate in order to avoid the accumulation of moisture. And lastly, the PuuMera journey has so far shown that, in order to erect larger scale wooden buildings, new partnerships networks need to be forged in order to sustain and increase innovative solutions and ways of working. Success Factors The multi-storey wood-frame building won shared first place in a competition based on the carbon footprint of buildings, organised by the Confederation of Finnish Construction Industries RT and the Green Building Council Finland. Continuous resident surveys indicate a very high user satisfaction. Novelty The project is a good example of challenging traditional ways – in this case constructing a multi-storey building out of wood instead of concrete – with profitability in mind, in this case innovatively linking climate benefits with business profit. Sustainability Impacts The VTT Technical Research Centre of Finland has defined the building as passive in terms of energy. It has an air-leak factor of less than 0,6 l/h. The building uses solar panels for electricity generation. The U-value (thermal transmittance) of the walls is 0,12 W/m2K and of the roof 0,08 W/m2K. The floors are constructed of wood, although, for thermal reasons, a concrete slab partitions the cold car parking level. The building’s wooden frame has a stud construction in large prefabricated elements with composite intermediate slabs and beams. The partition elements are cross-framed, as are the lower and upper beams. These techniques will be developed further in coming projects, where the will be to also construct thinner walls. The external walls are made from laminated timber. These are fitted with facade panels and boarding at the factory and delivered ready to the site. Windows and balcony doors are also installed in the factory. The intermediate floor elements consist of finished wooden elements, assembled on site. The sound insulation properties of the building have been excellent. The carbon footprint of PuuMera, Europe’s biggest wooden apartment building, is less than half of the carbon footprint of an average residential building due to the exploitation of renewable energy sources and its material choices. Overall, the carbon footprint is less than half of that of an average residential building. The carbon footprint of the building was successfully reduced through recycled, environmentally-friendly material choices. Recycled glass, hemp concrete and untreated wood were used in some parts of the facade. The building techniques will be developed further in coming projects, where a further aim will be to construct thinner walls. Challenges and potential for further development During the building process it became apparent that learning new skills is a prerequisite when seeking new and innovative ways of building. In this case, this entailed relearning skills almost lost during the overall transition towards concrete construction over the past 70-100 years. Contact person(s) for more information: Mika Airaksela, Managing Director, Building Company Reponen (Rakennusliike Reponen) mika.airaksela@rklreponen.com 358 500 70 3113