Lumber Building 4/

Oslotre AS


Project Details



Kristiansand / Norway



Year (Design/Construction):

- / 2023

Area (Net/Gross):

- / 3106 m2
Operational Carbon emissions

Operational Carbon emissions (B6) kgCO2e/m2/y:

Embodied Carbon emissions

Embodied Carbon emissions (A1-A3) kgCO2e/m2:

  • Regular glulam frame and slim hybrid CLT and concrete floor system.
  • Prefabricated pine wood cladding and wood fibre insulation.
  • All load-bearing timber structures are left exposed
  • Natural materials used through the interior; spruce panels on walls and wood-wool acoustic panels on ceilings and walls.
  • The wall to window ratio improves the thermal performance of the building.

“Lumber 4” is a commercial and office building spanning six floors. A recessed ground floor constitutes the commercial level, with the five floors above dedicated to office spaces.

The structure is composed of a masstimber construction with columns and beams made of glued laminated timber.

The floors are constructed using a composite structure of CLT and concrete, creating a slim and efficient floor system that spans long distances while also addressing fire and acoustic requirements.

Diagonals on the ground floor facilitate better vehicular access around the building. The existing communication core from adjacent building phases contributes to lateral stability and access to the office floors.

Between the third and fourth floors, an atrium with an internal staircase made of masstimber has been introduced. Wood elements are prominently displayed in the interior, providing warmth in winter and cooling in summer.

The facade is composed of prefabricated curved wooden elements in pine, treated with green paint. The eaves above the curved elements are straight, creating a curved shadow on the panel. Over time, the paint under the shadow will weather, leading to a changing facade with lighter and darker curved sections. The insulation used throughout is wood fiber. The cladding consists of fire-treated pine.

All load-bearing structures are exposed, and exterior walls are clad with white-pigmented spruce panels. Wood wool acoustic panels are used in concealed service areas and meeting rooms. Visible conduits are painted in a light beige color. The large floor-to-ceiling windows open up to the view and provide ample natural light.

The construction of the building was completed in record time, with detailed planning and construction taking only 12 months. “Lumber 4” has demonstrated that it’s possible to construct competitive timber buildings when compared to same technical standard concrete and steel structures. The building was 90% leased upon completion.

Oslotre served as the architect, interior architect, and timber structural engineer for the project.


  • Estimated Energy Consumption (kWh/sqm GFA (Gross Floor Area)) per year: 92.4 kWh/sqm Square meters GFA (Gross Floor Area) per employee or resident: 17 sqm.
  • Average U-value (W/sqmK): U-value for external walls – 0.21 U-value for floors against the ground and against the outdoors – 0.11 U-value for glass/windows/doors – 0.8 Air leakage rate – 0.5.
  • Brief Description: Energy Source: District Heating Ventilation: Ventilation system equipped with water-based heating coils.
  • Material Usage: The structural system is constructed of timber with columns and beams made of glued laminated timber. The floors are a composite structure of solid wood and concrete. All insulation is made of wood fiber. The cladding is fire-treated spruce.
  • Contract Type: Collaborative Contract Environmental Classification: BREEAM Very Good – Energy Rating A for office section, B for commercial space.


  • Client: Skeie Eiendom
  • Contractor: VEF Entrepreneurs
  • Project Management: Innovatre
  • Architectural Team Members: Jørgen Tycho Architect MNAL, Christoffer Imislund m.arch., Katrin Wilde Sampaio, Kristine Karklina
  • Interior Architect and Team Members : Amanda Skadeberg – Oslotre,
  • Landscape Architect and Team Members : Hanne Alnæs and Kaja Tellefsen Wivestad from Asplan Viak
  • Consultants: 
      • Structural Engineer (Wood): Oslotre AS
      • Structural Engineer (Concrete): Multiconsult AS
      • Structural Engineer (Building Services): Sweco AS
      • Acoustic Consultant: Sweco AS
      • Ventilation Engineer: Rivco AS
      • Electrical Engineer: Bravida AS
      • Water and Sewage Engineer: Vianova
      • Fire Safety Engineer: Rambøll
      • Fire Safety Engineer (Wood): Rambøll
      • Fire Safety Engineer (Concrete): Rambøll
      • Ecologist: Rambøll
      • BREEAM Consultant: Rambøll
      • Delivery of Solid Timber and Glulam: Splitkon
  • Photographers: Kyrre Sundal, Christoffer Imislund/Oslotre



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