New wooden blocks of flats complement the modern wooden neighbourhood of Linnanfältti in Turku

In autumn 2023, two new wooden blocks of flats will be completed in Turku’s Linnanfältti. They will complement a wider urban block that is part of the nationwide programme of promoting wooded construction. Sweco has been responsible for the structural engineering of these residential blocks of flats.

The housing company Portinvartija, constructed by Puurakentajat Group and FIM Varainhoito, complements the modern wooden neighbourhood of Linnanfältti (in Finnish) on Linnankatu in Turku. Linnanfältti is part of the nationwide programme that promotes wooden construction. Building began in this pilot area in 2017, and the estimated completion date of the new neighbourhood is in the mid-2020s. 

In autumn 2023, the block will receive two new residential blocks of flats, which will have a total of 58 homes. An air raid shelter is located on the basement floor of one of the buildings, while parking space and charging points for electric cars are available below the courtyard for all the block’s residents. 

The use of wood reduces Portinvartija’s carbon footprint, but an ecological lifestyle is also supported by Linnanfältti’s location; the services of the city centre, Turku Harbour and the city bike stations are all without a walking distance. Furthermore, walking and cycling routes along the Aura River and several cultural attractions, such as Turku Castle, are also nearby. 

Functioning solutions exist for wooden construction

According to Group Manager Susanna Friman from Sweco, both of the Portinvartija buildings use the same structural system, a wooden CLT frame. CLT can also be found in the intermediate floors. These structures have been shown to work. 

‘We are no longer completely new to wooden construction, and so we are able to leverage good experiences from previous projects,’ she says. Wood has also been used as a decorating material in the homes and stairwells of Portinvartija. 

The most challenging aspects in terms of structural engineering were the buildings’ load-bearing lines and space types, which were not vertically aligned across all the floors. ‘Structural engineers had to consider the structural details carefully in order to sensibly transfer loads and efficiently design the spaces from an engineering perspective.’ 

No need for an expensive weather shelter

The land allocated for the two residential blocks of flats was so small that a decision was made right at the beginning of the project to not have a weather shelter, which is typically used when building with wood. Instead, the designs were based on an alternative solution. 

‘By using the correct details, we were able to protect the structures from the elements during construction,’ Friman says. Because one side of the load-bearing partition walls between the flats was constructed using glued laminated timber frames, the wall could not be insulated or sheeted until the entire floor had been protected from the weather. 

The design schedule was tight, but the end result matches the client’s requirements. ‘This project continued our well-functioning collaboration with Puurakentajat, which we have established over the course of several other projects,’ Friman says. The new wooden blocks of flats form a coherent combination with the block’s other wooden buildings, including the previously completed Lyhdynkantaja. 

Picture: Puurakentajat Group Oy