Sobrespu

To fight climate change, countries set carbon budgets to keep emissions within safe limits. In Switzerland, SIA 390/1 defines how much CO₂ the building sector can emit during construction and use.

But outdoor spaces are often left out. These areas are still part of the project and can have a real carbon footprint. Ignoring them means underestimating emissions from built environment management.

How significant are outdoor surfaces in a building’s overall impact?

The study focuses on surfaces used by pedestrians and light motorised vehicles, with a functional unit of one square meter of low-traffic outdoor surface over a 60-year lifespan.

The approach involves:

• Identifying the most commonly used pavement materials

• Performing a Life Cycle Assessment (LCA) to determine the carbon emissions associated with each material

• Calculating the carbon footprint of the different pavement types

Outdoor surface materials show a wide range of carbon impacts depending on thickness and type. Gravel has the lowest footprint (0.17 kg CO₂/m²·year). Imported stone increases emissions by about 25% compared to local sourcing. Perforated concrete has 1.8 times less impact than conventional concrete paving for the same thickness. Polished stone triples the impact compared to grounded stone. Cement-bound solutions add an extra 0.25–0.3 kg CO₂/m²·year.

Since outdoor surfaces can represent up to 20% of a building’s future carbon budget, reduction strategies are key:

• Use low-carbon, locally sourced materials

• Minimize thickness and overall material use

• Favor perforated concrete over full concrete paving

• Limit paved areas

• Avoid cement-bound and non-reversible solutions

• Restrict polishing and unnecessary finishes

Further details can be found in the publication, and a dedicated tool has been developed and made available.

https://www.buildinglowcarbon.com/our-tools/sol-impact