Housing developments Helsingin Rauduskoivu and Helsingin Mänty

This project’s aim was to develop a competitive alternative to the prevailing construction method employed for residential multi-storey buildings. On the other hand, we set out to create an area of wooden multistorey residential buildings that provides the prerequisites for comfortable living. Planning was based on a vision for a milieu of wooden multi-storey buildings, not on individual multi-storey residential buildings. The objective set for the group of three- and four-storey buildings was that it should provide a humane living environment that would also be economically sufficiently efficient for urban construction.

The project was implemented in cooperation with the City of Helsinki, which became involved already at the plot allocation stage. In the town plan, the area was envisaged to contain townhouses, whose form was to be agreed on together.

The frame

A need for adequate floor-level efficiency, as well as proportions and geometry characteristic to LVL structures, guided the design process. In the apartments, we aimed to avoid multiple corners.

The multi-storey building system consists of an LVL column-beam frame, ribbed slab intermediate floors and ceiling elements, and exterior walls made of prefabricated wooden modular units. The advantage provided by the frame solution is its modifiability. The absence of interior bearing walls enabled floor plans where apartments of various sizes could be placed on top of one another. It is also easy to combine and divide apartments afterwards. Slanted roof elements enabled airy interior space for the top-floor apartments, and the high ceiling also allows the building of a loft.

The balcony structures and sun visors were mostly LVL and glulam structures hung outside the frame, which is a good solution for moisture control and cold bridges. The split glulam exterior panelling is 42 mm thick and 12 metres long at its longest.

This solution set out to speed up the building schedule, reduce on-site work and minimise material wastage. In theViikki case, the frame and intermediate floor construction stage is very short.

Acoustic design has an important role in the construction of wooden multi-storey buildings, especially in the controlling of low frequency noise. Acoustic measurement results are very good and clearly exceed the current building regulations.  Wood creates a pleasant acoustic environment for the staircases. 

HVAC

The buildings have hydronic radiator heating and a water mist sprinkler system. The systems were integrated with the other HVAC solutions and the LVL beams. The modelling of the building’s frame and the HVAC networks allowed us to make impact assessments and ensure the compatibility of the various plans.

An automatic fire extinguishing system provides a high level of fire-safety for the apartments. When the fire extinguishing system is activated, it produces a mist of water, which means that the amount of water used remains small (1.4 l/min) and significant water damage will not incur.

The project was planned before the renewal of the E1 fire regulations, which did not allow any wooden surface to remain visible in the apartments, but the wooden frame and stairwells are visible in flights of stairs.

The carbon footprint

The project included the calculation of the carbon footprint of one wooden multi-storey building and the energy consumed during its construction, as well as calculating the building’s carbon footprint over one hundred years. The results showed that the carbon footprint of a wooden multi-storey building (347 t CO2 equivalent) is 45 per cent smaller than that of an equivalent concrete building.

Material production for a wooden multi-storey building required more than four per cent less energy than an equivalent concrete building. Over a period of one hundred years, the carbon footprint of a wooden multi-storey building is 3928 t CO2equivalent and its energy consumption is 63.2 TJ, which includes the energy required for material production, transport, repairs, the construction stage on the site and heating.

This project is the largest wooden multi-storey building project in Finland so far. The Metsä Wood multi-storey building system has been developed for many years, and has been used in the construction of wooden multi-storey buildings not only in Finland but also in Germany, France and Italy.