when the architectural value constructs environmental quality

project characteristics

Located within the green belt of Brussels opposite the exceptional natural site of the Forêt de Soignes, Solaris is the first office building to be certified for High Environmental Quality (Valideo) in the Capital of Europe. It sets a new standard in saving natural resources and stressing sensible use of renewable energy: photovoltaic and geothermal.

programnew construction of an office building, pilot project dedicated to sustainable construction • perfect combination between design & energy performance
clientHippogone, member of Herpain-Urbis Group
addresschaussée de La Hulpe 120 • 1170 Watermael-Boitsfort
building typework
expertisesarchitectureinterior architectureproject managementconstruction managementfeasibility studiesprogrammingbuilding audit
size22.571 m²
team• client: Hippogone, member of Herpain-Urbis Group
• structural engineers: association Soliprom + Ney & Partners
• services: Energies 3E
• contractor: Herpain sa
• landscape architect: Dominique Eeman

In order to create a significant diversity in the interior spaces, offer great occupational flexibility, and, most of all, to maximize natural light, the designers created 2 facades with large glazed atria of 3 levels. In order to be more outstanding, the projects explores all the possible options, regarding sustainable development: geothermal science, photovoltaic cells, reinforced insulation, solar protection, recovery of rain water, natural cooling, water solar heating …


• facades in natural stone, curtain wall, photovoltaic panels
• interior: 2 huge halls on 3 levels, natural stone, & wood

energy performance

• overall thermal insulation level: K39 (EPB requirement = K45)

• primary energy consumption level calculated for 2005 (reference year) for an open-plan office: E74 (EPB requirement = E90). Excluding geothermal power, the primary energy consumption level would be: E93.

By partitioning the offices (< 30m²), the primary energy consumption level could be reduced to E71 or E70 depending on the choice of adapted lighting controls (automatic light control with a presence sensor or manual control with automatic switch-off when nobody is there).

• geothermal power:
in winter: the heat pump (non-reversible water/ground pump, 200kW) provides heat through ceiling panels. The remaining energy needed is produced by 2 condensing boilers (2x 200kW)
in summer: geothermal cooling (via a 300kw heat exchanger) cools the building through ceiling panels. The remaining energy needed is produced by 1 condensing cooling machine (641 kW)

• solar panels: total peak power = 95,120Wp (30,380Wp + 64,740Wp) total output: 72,734 kwh (17,852 kwh + 54,882 kwh) the solar power output covers 100% of the electricity consumption of the HVAC system (30.000 kwh for the cooling system

• rainwater collection (flushed water, garden watering etc.): capacity: 124m³ (50% storage – 50% reserve)

• glazing performance: super-insulating double glazing: U = 1.1 shading coefficient: SC = 0.28 (SC = 0.11 in combination with the solar panels on the south-facing side


• 2009: winner of a Belgian Environment & Energy Award 2009, in the category “Eco-building Award”, Brussels, Belgium. This award underlines the commitment of the developers to respecting the environment in all its forms and contributes very significantly to sustainable construction practices

• in 2010: winner of the MIPIM Award in the “Green Buildings” category, in Cannes, France