Sustainability Report

Life cycle assessment data prepared in line with SIA 2040 shows that 543 HORTUS performs significantly better than Swiss benchmarks, both in embodied impacts from construction and in operational energy use. (SIA 2040 is the Swiss Society of Engineers and Architects’ benchmark for the energy and carbon performance of buildings, covering both embodied and operational impacts.)

Embodied carbon (construction/materials)

CO2 footprint

• HORTUS: 5.3 kg/m2 ERA/a
• PV (extra): +1.5 kg/m2 ERA/a
• SIA 2040 benchmark: 9.0 kg/m2 ERA/a

Grey energy (embodied energy)

• HORTUS: 21.3 kWh/m2 ERA/a
• PV (extra): +1.9 kWh/m2 ERA/a
• SIA 2040 benchmark: 40 kWh/m2 ERA/a

(ERA, or Energiebezugsfläche, is the Swiss standard “energy reference area” — the floor area used to calculate and compare energy demand and emissions per square metre.)

Measures to reduce embodied carbon

• A hybrid clay–timber floor system replaces concrete slabs with prefabricated timber frames filled with compressed clay. Embodied carbon is estimated at one-tenth of a comparable concrete slab.
• Timber is harvested from nearby forests and clay is excavated directly from the construction site, then processed in a temporary on-site field factory.
• With no basement, concrete use is reduced. Instead, the building stands on shallow point foundations/stilts.
• Isofloc ECO, made from recycled paper and supplied in large bales, provides insulation.
• The material palette was consciously reduced to wood, clay, cellulose, and steel for recyclability and clarity of life-cycle assessment.

Operational energy (use phase)

CO2 footprint

• HORTUS: 0 kg/m² ERA/a (geothermal + PV, no fossil fuels)
• SIA 2040 benchmark: 4.0 kg/m² ERA/a

Operational energy demand

• HORTUS: 33.17 kWh/m² ERA/a
• SIA 2040 benchmark: 80 kWh/m² ERA/a

Energy production (on-site PV)

• HORTUS: 66 kWh/m²/a (more than double operational demand)
• Result: Surplus offsets embodied energy → full amortisation in ~31 years

Measures to reduce operational emissions

• Geothermal energy provides heating and cooling, eliminating fossil fuel use.
• 5,000 square metres of solar panels across the roof and parapets generate ~800,000 kWh/year — more than double the building’s energy demand.
• A compact form minimises the surface-area-to-volume ratio, reducing heat loss.
• With its raised structure, air circulation beneath the building stabilises indoor temperatures (cooler in summer, warmer in winter).
• Controlled ventilation systems with heat recovery, humidity regulation, and sensors for carbon, VOCs, and aerosols ensure a healthy and efficient indoor climate.