Wooden apartment buildings in Sipoo’s Söderkulla

A-Kruunu completed construction of two four-storey wooden apartment buildings in Sipoo’s Söderkulla in the summer of 2021. In addition to the residences, the complex includes bike sheds with horizontal lattice walls. There are 47 rental apartments in total, and they are all interest subsidised by the Housing Finance and Development Centre of Finland (ARA).

Read the article in Finnish: Sipoon Söderkullan puukerrostalot

Opening to the west, the plot is in a fairly hilly location next to a park with plenty of visible bedrock. The placement of the buildings follows the natural contours of the terrain, forming a protective perimeter along Kalliomäenkaari street to shield the parkside grounds from traffic.

The dark colour of the facades and the more vibrant shade of the balcony walls come together to create a calm yet distinctive mix and are a subtle fit for the surrounding forests and boulders. The building’s architecture has been influenced by the limits of wood construction and volumetric elements, such as the maximum dimensions of modules and the restrictions stemming from fire regulations.

The plot’s boundaries add their own touch to the shape of the buildings and the layout of the yard. The apartment modules have for the most part been designed to follow the building’s outer shape. Windows on the long outer walls of the apartments begin near floor level. They face in directions with abundant sunlight, making the apartments more pleasant and providing beautiful views that extend far towards the horizon.

The interior materials exude brightness and warmth. Ceiling acoustics are improved with cement-wood fibre board that brings an added softness to the soundscape and is also visually appealing. The stairwells are bright and airy, with natural light from the skylight running top to bottom and providing a more spacious feel.

With the exception of the civil defence shelter, the building’s construction is based on volumetric elements and a balloon frame. Glulam was used for the stairwell support beams, black alder panel for the ceilings of the bathrooms and sauna, and horizontal wood panelling for the facade cladding. Balcony tiles are made from CLT sheets.

In the landscaping design, much consideration was given to the park-like environment and terrain, parking space locations, surface materials, play areas, ornamental plants, and storm water absorption.

Technical solutions

The buildings have an SFS 5982 type 2 sprinkler system. The wood panelling of the ground floor facades is treated with fire retardant. The fire dampers are located between the storeys in the facade’s ventilation gap.

Ventilation is mechanical and apartment-specific. District heating and water circulated floor heating provide heat for the buildings, and there are radiators in the common corridors.

Construction project

The project’s preliminary draft was an appendix to the turnkey contract tender and was updated somewhat once the contract winner was clear. Its basic principles remained unchanged, however.

Specific design work took six months. Industrial prefabrication and the on-site excavation and foundation work ran simultaneously in June 2020. The project handover was at the end of March 2021, with the growth of the vegetation still inspected in June 2021, among other checks.

The project taught its participants that there is still plenty of untapped potential in prefabrication, for example for stairwells and balconies.

Careful planning, industrial prefabrication, and quick installation on site were all important cost saving factors. In addition, the building’s low height of under 14 m meant it fit into a lower sprinkler class, further lowering costs.


The Oulu-based Avario specialises in wooden construction and in designing daycare centres, retirement homes, and schools. Their comprehensive design expertise extends to wooden multi-storey buildings, with a special focus on superior architecture and the intelligent use of sites and interior spaces – without forgetting lifecycle effects.

Project in brief


  • Location | Söderkulla, Sipoo
  • Purpose | Residential apartment building
  • Constructor/Client | A-Kruunu Oy
  • Valmistumisvuosi | 2021
  • Floor area | 3 791 m2
  • Volume | 12 830 m3
  • Investointikustannukset | 8 516 147 €
  • Architectural Design | Arkkitehtitoimisto Avario
  • Structural design | BD-Con Oy
  • LVIA-suunnittelu | Insinööritoimisto Airlon Oy
  • Electrical design | Valosel Oy
  • Interior design | Arkkitehtitoimisto Avario
  • Pääurakoitsija | KW-Component Oy
  • Wood component supplier | Woodcomp Oy
  • Photographs | Jari Härkönen, Arkkitehtitoimisto Avario Oy
  • Text | Markku Ranne