Powerhouse Kjørbo

Renovation of the building - Powerhouse Kjørbo demonstrated that it is possible to renovate existing properties into energy-plus buildings even in Norwegian, cold climate., Such renovations make commercial and environmental sense to all parties involved. A holistic approach to the project that simultaneously considered materials and embodied energy, technical systems, architecture, and energy efficiency and generation over the lifespan of the buildings was crucial to achieving the project’s ambitious objectives.

Powerhouse Kjørbo is going to be an important demonstration project for plus-energy buildings, both in Norway and abroad, which will influence green refurbishment projects in the future.

The Kjørbo buildings were certified to BREEAM- NOR “Outstanding” classification for the design stage. BREEAM is the world’s leading design and assessment method for green buildings and BREEAM-NOR is specifically adapted to Norwegian standards and criteria. There are five assessment levels in BREEAM-NOR, and “Outstanding” is the highest possible level. In addition, the buildings fulfill all the requirements of the Norwegian Passive House standard for commercial buildings. Powerhouse Kjørbo is also a Norwegian Zero Emission Buildings (ZEB) pilot, as part of a project run by the Research Centre on Zero Emission Buildings that aims to promote very low carbon emissions during the lifetime of buildings. Powerhouse Kjørbo was nominated for the 2014 Norwegian Technology Award for its outstanding energy performance.

(Source: http://www.sapagroupmedia.com/share/download.php?docid=doc6icp7szwq681yhc07uo&type=original )



Providing optimal technical system
Optimizing the envelope of the building
Renewable energy usage


240 kWh/m2
annual delivered before (incl. data facilities)
50 kWh/m2
annual delivered after (including data facilities)
20,4 kWh/m2
annual delivered after (without data and technical equipment)


per m2: € 2.654

1. Case background

Reason of the renovation

The renovation included two office buildings out of a total of nine of the entire site from 1980s. Both were to be refurbished to a plus energy standard using high insulation standard, Pv and ground coupled heat pump. The building was supposed to become a powerhouse. There were no past energy renovations. Skanska was the main consultant of the renovation. The whole process started in 2013 and ended in 2014.

More information

Powerhouse is a type of a building that during its lifecycle, produces more renewable energy than it consumes for construction and maintenance. The building was supposed to be renovated within commercial marketable conditions. The energy production must have been based on energy sources on site or nearby with access from the site.

What is more, the energy use for electrical appliances should have not be included in the energy balance account. The target BREEAM classification score was supposed to be “Outstanding”. Beside, one of the green aspect goal was to reduce the electricity costs by 100% in comparison to the conventional Norwegian office building. Another objective was to achieve Healthy indoor environments by saving 10% of water use environmentally friendly materials.

The building was renovated by Skanska, which is a part of Powerhouse Alliance. This association is constructing multiple energy-positive buildings in Norway. Powerhouse Kjørbo was the first project of the Alliance. The idea of the renovation was born in 2011. The contract with the main contractor was signed at 18.03.2013 so the work had started. The renovation was completed in 2014.

(Source: http://www.sapagroupmedia.com/share/download.php?docid=doc6icp7szwq681yhc07uo&type=original )

Country and it’s climate

The building is situated in Sandvika, 15 km from Oslo (Norway) from the northeast to the southeast side, with a highway with heavy traffic on the northwest. Southern Norway features a temperate humid continental climate with fairly warm summers and mild winters (for such climate zone)

More information

Precipitation in Norway varies between 500 and 3000 mmm per year. Southern part of a country never has continuous daylight, though it averages 19 hours of daylight a day in midsummer. Those parts, have a Cfb Climate* according to the Köppen classification** , a warm temperate humid climate with the warmest month lower than 22°C over average and four or more months above 10°C over average.

*Cfb - Marine west coast climate, major climate type of the Köppen classification characterized by equable climates with few extremes of temperature and ample precipitation in all months. It is located poleward of the Mediterranean climate region on the western sides of the continents, between 35° and 60° N and S latitude. Precipitation totals vary somewhat throughout the year in response to the changing location and intensity of these storm systems, but annual accumulations generally range from 50 to 250 cm (20 to 98 inches), with local totals exceeding 500 cm (197 inches) where onshore winds encounter mountain ranges. Not only is precipitation plentiful but it is also reliable and frequent. Many areas have rainfall more than 150 days per year, although the precipitation is often of low intensity. Fog is common in autumn and winter, but thunderstorms are infrequent. Strong gales with high winds may be encountered in winter.

(Source: https://www.britannica.com/science/marine-west-coast-climate )

**Köppen climate classification - widely used, vegetation-based empirical climate classification system

(Source: https://www.britannica.com/science/Koppen-climate-classification )

Building type

Powerhouse Kjørbo is a typical office building with about 240 occupants and 12 hours per day of the utilization.

(Source: http://task47.iea-shc.org/data/sites/1/publications/SHC_Task47_STC_report_11SEP2015.pdf )

3. Methods & materials used

The main strategy of the building’s design was based on:

  • Providing optimal technical system
  • Optimizing the envelope of the building
  • Renewable energy usage

The black glass façade* of the building was replaced with a new one made of charred wood panels** and also window frames made of aluminium. The constructors were reusing and incorporating existing structures and building elements.

What is more, the Powerhouse consortium equipped the buildings with new energy, ventilation, heating and lighting systems.

More information

The main idea for the renovation was to use environmentally responsible (eco-friendly) materials from a lifecycle perspective. One of the elements, the charred wooden façade is a natural material that is designed to have a long and relatively maintenance-free lifespan. Materials were retained and reused in the building where possible, such as the structural elements. Many new elements added to the buildings were intended to be easily reusable after usage: e.g. aluminium window profiles. The new windows were designed to allow a high level of daylight transmission and distribution in the rooms to reduce the need for artificial light.

The whole renovation focused mainly on reducing thermal bridges***.

The renovation according to the thermal bridges:

  • Mounting of new windows
  • Insulation thickness where concrete slabs meets the façade
  • Wood facade construction with few thermal bridges, and 200 mm insulation in front of slabs

Overall demand to thermal bridges are: < 0,03 W/m2 k

Ecological materials:
  • Building materials with lowest possible embodied energy****
  • Charred wood for façade cladding
  • Labelling materials or materials with low polluting according to EN 15251*****

The consortium was the first who used the BIM - Building Information Modelling. Such modelling is was based laser scanning on the Kjørbo project. It was supposed to map and model the exterior and interior parts of the building. The building’s exterior façade and the surrounding trees were accurately modeled using laser scanning to enable detailed BIM solar studies to calculate the extent of shading from trees and to optimize the placement of roof-mounted solar panels. Laser scanning was also used to create an accurate as-built BIM model of the building’s load bearing structure, which was retained and incorporated into the refurbishment.

(Sources: http://task47.iea-shc.org/data/sites/1/publications/Task47-Power-House-Kj%C3%B8rbo-Norway.pdf

http://www.sapagroupmedia.com/share/download.php?docid=doc6icp7szwq681yhc07uo&type=original )


*Façade is generally one exterior side of a building, usually, but not always, the front. From the engineering perspective of a building, the façade is of great importance due to its impact on energy efficiency

(Source: https://en.wikipedia.org/wiki/Facade )

** Charred wood - The wooden material created from the burnt planks on both sides to the desired amount of char. The carbon exterior releases the moisture inside the board as gas and steam. Then he boards are being cooled, brushed and washed to aesthetic liking of the user. The amount of char cleaned off changes the look of the wood. Finally, the board is sealed with a natural oil or left it unvarnished.

This method of burning the surface of wood building materials began in Japan 300 years ago. Since Japanese builders traditionally used cedar, as well as cypress, the process is called shou sugi ban, or “burnt cedar”. Using charred wood for construction is a viable eco-friendly option, particularly since this completely natural manufacturing process requires only fire and wood; the harsh chemicals used in pressure-treated lumber are eliminated. Shou sugi ban also yields an extremely durable building material. Wood treated with fire is paradoxically fire resistant, as well as resistant to insects. The material is also durable due to its low reactivity and is rated to last 80 years.

(Source: https://architizer.com/blog/burnt-is-the-new-black/ )

***Thermal bridge is a localised area of the building envelope where the heat flow is different (usually increased) in comparison with adjacent areas (if there is a difference in temperature between the inside and the outside).

The effects of thermal bridges are:

  • Altered, usually decreased, interior surface temperatures; in the worst case this can lead to moisture penetration in building components and mould growth.
  • Altered, usually increased, heat losses.

(Source: https://passipedia.org/basics/building_physics-basics/thermal_bridges/thermal_bridge_definition )

**** Embodied Energy is the energy requirement to construct and maintain the premises, for example, with a brick wall, the energy required to make the bricks, transport them to site, lay them, plaster them and (if necessary) paint and replaste over the life of the wall.

(Source: http://www.yourhome.gov.au/materials/embodied-energy )

***** EN15251 specifies indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics

(Source: http://www.rehva.eu/publications-and-resources/rehva-journal/2012/042012/revision-of-en-15251-indoor-environmental-criteria.html )

4. Costs

The cost for refurbishment: 2 654 €/m2.

The Powerhouse Kjørbo was to be built within commercial marketable conditions. The enterprise Enova supported the project with US$ 2.7 million through the program New Technology in Buildings of the Future, and the Passive House program. The rent was higher than for a similar office building with an average energy standard. However, when the reduced energy costs are included, the total cost for the tenant was at about the same level as for a standard office building.

(Sources: http://task47.iea-shc.org/data/sites/1/publications/Subt.A%20Summary%20report.pdf

http://www.sapagroupmedia.com/share/download.php?docid=doc6icp7szwq681yhc07uo&type=original )

5. U-value & energy savings

The buildings were redeveloped to ensure very low energy consumption through a well-insulated and airtight building envelope that meets Norwegian passive house standards for commercial buildings (NS 3701).

U-value (thermal transmittance) is the rate of transfer of heat through a structure divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be.

  Walls Roof Windows Ceilings Floor
Before ~0.3 ~0.2 ~1.8 ~0.3 -
After 0.15 0.08 0.8 ‘’0.3 0.12-0.16

Therefore, because the U-Values have decreased, one can conclude that the energy consumption decreased.

Energy savings:

Annual delivered before: 240 kWh/m2 (including data facilities.)

Annual delivered after: 20,4 kWh/m2 (without data and technical equipment); 50 kWh/m2 year (including data facilities)

(Source: http://task47.iea-shc.org/data/sites/1/publications/Task47-Power-House-Kj%C3%B8rbo-Norway.pdf )