Compact and efficient shape to achieve the net zero energy

In 2011, the Treurenberg building dating from the 1960s was the subject of an architecture competition, the idea being to redevelop the site to create mainly office space. The option of total demolition and reconstruction was retained in order to put up a new building compliant with current local and technical standards using progressive building solutions to achieve the ultimate aim of creating a net zero energy building certified “Excellent” by BREEAM.

The challenge facing the architects was to design a high-quality office building in the city centre close to the institutions and travel hubs that would also fit into the historical urban context by exploiting the existing heritage. At the same time, they were tasked with making the building energy efficient in line with the BREEAM ‘Excellent’ certification. The outcome of this brief was a compact building around an asymmetrical atrium that would reveal the remains of Brussels’ first city walls.

There is no doubt that the most striking original feature of the building is the showcase it offers for Brussels’ first city walls. A patio has been created between the building and the wall, making it visible from public space and allowing the creation of small garden filled with vegetation. The entrance to the building is largely glazed over two floors, which helps to provide an excellent visibility to the tenant by creating a strong visual link, allowing its occupiers to benefit from the light-flooded atrium. To achieve the zero energy target and the BREEAM Excellent certification, the building has been given a compact and efficient shape. It is hinged around an atrium that reaches up from the patio on the underground level to the 5th floor that boasts a stunning indoor terrace affording wonderful views over Brussels’ historic centre. The 5th floor also opens onto an accessible outdoor terrace. The atrium generates a source of natural light and creates a pleasant friendly environment atmosphere. The building is built in natural stone from France and integrates perfectly with the existing historic buildings. The interior layout with its elegantly simple black and white theme combined with one colour and wood radiates an atmosphere of quality and rigour, offset by the warmth of the natural wood features.


Unique flexibility

With total office space of 9.812 square metres, for an overall capacity of 710 people, the Treurenberg office space is designed to be rational and extremely flexible. The office floors can be divided up as required and are ideal for open spaces or individual offices.

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Floor Plans

Floor M2
Seventh 657
Sixth 778
Fifth 1056
Fourth 1495
Third 1495
Second 1489
First 1265
Ground 469
-1 (offices) 1108
Archives 336
Archives 336
Parking 58

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Technical specifications


  • Heat generation by two high output gas condensation boilers ;
  • Cool air generation by two highly energy-efficient refrigerating machines connected to a cooling tower that can be run in free chilling mode ;
  • Ventilation unit with variable air flow rate depending on the occupancy of the building with high output heat recovery wheel ;
  • Fresh air reserve for adding meeting rooms (maximum 12.5% of surface areas) ;
  • Maximum density of people: 1 person per 8m ;
  • Metal ceilings radiating reversible hot and cold ;
  • Variable water flow rate in the hydraulic circuits to reduce electric power consumption ;
  • Fresh air intake (36 m3/h/person) with motorised valves driven by presence detection for two 1.35 m modules ;
  • Ambient temperature control by two 1.35 m modules - adjustable (+/-1.0°C around a set point) by the occupant ;
  • Control, power metering and alarm monitoring via centralised technical management ;
  • Temperature conditions: winter: minimum T°: 21°C/summer: maximum t°: 25°c (per 30°c outside maximum) Overheating benchmark according to passive standard.


  • TL5 light fitting with high frequency ballast controlled by communication bus and addressable system ;
  • Office lights controlled by push button and absence detection by two 1.35 m modules ;
  • All office lights are dimmable, using twilight probes that adapt the power consumption of the artificial lighting according to the amount of sunshine ;
  • Lighting level: 500 lux on work area ;
  • Lighting control of corridors, stairwells, washrooms, showers, lift shafts and car parks by presence detection.


  • Mixed wood-aluminium frame with triple glazing and outside slatted blinds automatically adjusted to the level of sunshine and the air temperature settings inside the offices ;
  • Façade insulation: 21 cm thick (λ = 0.024 W/mK) ;
  • Upper floors of façades (+5 to +7) clad with photovoltaic panels, with estimated power generation of 40,860 kWh/year ;
  • Lower façade floors clad with natural stone ;
  • Optimisation of glazed areas to improve visual and thermal comfort of the occupants.


  • Roof insulation (average thickness): 25 cm thick (λ = 0.024 W/mK) ;
  • Roof-mounted photovoltaic panels: estimated power generation of 89,555 kW/year.


  • Option of maximum two customer-occupants per floor ;
  • Modulation of office platforms: 135 cm ;
  • Office floor-to-ceiling height: 2.70 cm ;
  • Raised floor: 12 cm ;
  • Car park clearance: 2.40 cm ;
  • Option of two kitchenettes on each floor ;
  • Option of adding an access control system on each floor ;
  • Indoor (95 m2) and outdoor (332 m2) panoramic terrace overlooking the centre of Brussels.

Car parks

  • 59 car parking spaces on two basement levels ;
  • 49 bicycle spaces.


  • Rainwater recovery to supply lavatories and urinals ;
  • Control of washroom consumption by way of presence sensors and water leak detection in the general supply ;
  • Shower rooms and cloakrooms ;
  • Two Gentlemen, Ladies and reduced mobility washroom units on each floor ;
  • Visitor washrooms in the entrance hall.


  • 4 lifts split in two duplex including:
    • 2 lifts of 800 kg ;
    • 1 lift of 800 kg and 1 goods lift of 1000 kg ;
  • Option of adding a visitor lift between the car parks and the entrance hall.


  • Maximum noise level in the rooms occupied: LAeq: 40 dB(A).

Fire protection

  • Fire detection devices in the entire building ;
  • Sprinkler system in all rooms on the office floors ;
  • Overpressure of emergency stairwells in case of an evacuation ;
  • Mechanical smoke clearance from the atrium.


  • Net Zero Energy pre-certification ;
  • BREEAM Europe Commercial 2009: Excellent.