Nurmijärvi’s wooden apartment complex

Jouhisarankuja Street in Klaukkala is home to a new complex of three wooden apartment buildings. Leveraging the BoKlok concept, two of the buildings are A-Kruunu rentals and one was sold by BoKlok as owner-occupied apartments.

Read the article in Finnish here.

Asunto Oy Nurmijärven Kaunokki and A-Kruunu Nurmijärven Jouhisarankuja combine to create a wooden apartment complex bordered by Lepsämäentie, Jouhisarankuja, and Vanha-Klaukantie streets. This block has three 5-storey residential buildings and one single-storey commercial building. Two of the residential buildings are A-Kruunu rental properties, while Asunto Oy Nurmijärven Kaunokki was built on the BoKlok model and sold to individual residents while under construction. There are a total of 90 apartments, of which A-Kruunu owns 63. Parking is at street level, separated from Lepsämäentie Street by a concrete noise barrier.

Constructed using the concept’s volumetric elements, the project benefited from a remarkable level of prefabrication. While the design language is minimalist and rational, the texture of the material stands out from afar, setting it apart from its concrete neighbours. In line with the mandated construction method, the façades are painted in light, muted colours that blend into the fields surrounding the location.

The frames are mostly wood, and the façades are clad with horizontal wood panel. All buildings have a gable roof. To accommodate a civil defence shelter, the ground floors of the residential buildings are partially concrete. All apartments and stairwells are constructed from pole-framed volumetric elements that were prefabricated to the absolute limit possible, with the surface materials, furnishings, and equipment all pre-installed at the factory.

Each apartment is made from 1–3 volumetric elements, meaning that the walls between any two apartments are created by the wall structures of two elements. The elevator shaft is made of CLT except on the ground floor. Apartment balconies are included in the volumetric elements, which significantly improves work safety and reduces on-site installation time. Fire regulations limit the amount of visible wood surfaces in the interiors: although the stairway stiles are CLT, the steps themselves are concrete.

Technical solutions

The wall, floor, and roof structures of the volumetric elements use a wooden pole frame with the conduits and joints needed by the required fire compartments and acoustics. Each apartment is its own fire compartment, and a separate building technology shaft that runs through the apartments constitutes another separate fire compartment. The residential buildings are in fire class P2 and the storage building is P3.

All residential buildings and premises, including the concrete structures on the ground floor, are equipped with sprinklers. In apartments, the sprinklers are hidden in walls or ceilings to maximise visual appeal. In other areas, the sprinklers are visible or concealed depending on the structure and purpose of the space. The building also has mains-connected fire alarms. The sprinkler system is connected to a fire alarm centre, which acts as a central relay point for the buildings and automatically informs emergency services of a sprinkler’s activation.

Vibration isolators will be installed between the volumetric elements according to a separate site-specific plan.

The construction project

Thanks to Skanska’s preparatory work, the municipal zoning for the block’s three lots allowed wood construction. This was a good fit with the BoKlok concept and its standard solutions.

The building permit was granted in June 2022 mere months after application, and the permit process with the Nurmijärvi authorities went smoothly.

Thanks to shared experiences with previous projects, everyone from clients and designers to the construction company and volumetric element supplier cooperated effortlessly in the planning and design phase, and the concept’s standard solutions made the process swift.

Construction began in August 2022 and took place on all three plots at the same time. Earthworks and foundations were ready first at the end of 2022. Factory production of the volumetric elements began at the same time, with the client, contractor, and supervisors conducting regular inspections.

Installation of the volumetric elements began in the first building in late January 2023. By early March, everything was in place. The installations cascaded one after another with about 2–3 weeks between phases. Installation took roughly two weeks per building, and the volumetric elements were installed on schedule. Each building’s roof and façade installations began immediately once its volumetric elements were in place.

Apartment interiors and stairwells were next, and the HVAC and sprinkler systems were connected once the building exteriors were complete. Installers worked in the communal areas at the same time. Finishing touches to the apartments, communal areas, and yards were added in August 2023. Various parties conducted the necessary measurements, adjustments, and inspections before the complex was handed over to clients as scheduled in October 2023.

Lessons learned: In this project, the time spent in the construction phase had room for improvement. In addition, the coordination of contract boundaries proved particularly important due to the use of volumetric elements.

A comment from the architect (Mikko Rosti): In 2017 when the local municipal zoning was still a mere draft, we were commissioned to study the potential of applying the BoKlok concept locally. With the construction method and zoning drafts for the area (Vanha-Klaukka) in hand, we made a proposal for three plots. Zoning for these plots then continued based on our ideas. Cooperation with the zoning authorities and building control went smoothly from the initial zoning draft to the building’s final design.

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