Decreasing the carbon footprint of energy efficient buildings, what comes next?

A full LCA was conducted to explore the contribution from each life cycle stage to the carbon footprint of energy efficient buildings, and the role of bio-based materials as future potential alternatives to decrease further carbon emissions in the building sector. Eight different design alternatives with comparable functionality were evaluated for Walluden, a four-storey multi-family building in Vaxjo, Sweden. The designs include three different building systems; volumetric modules, massive timber structural elements and a column-beam structure as well as the original design of the building from 1995 both with wood and concrete frame structures. The three new designs were modelled under conventional and passive house energy efficiency categories. A square meter of living area was used as the functional unit, and a service life of one hundred years was assumed. The analysis includes processes from raw material extraction, manufacturing of building materials, construction, energy generation for the use phase, selected maintenance activities, demolition and disposal of the building waste. Concrete carbonation phenomena, carbon storage and end-use benefits from substituting fossil energy effects with wood material waste were also explored. The results show that the benefits of more use phase energy efficient designs are significant, but as the use-phase impact lowers and there is less improvement potential; both the production and end-use phase become more relevant. Indeed, for the passive house design, the production phase carbon footprint is of the same order as for a one hundred years use phase. For the production phase, increasing the share of bio-based products can decrease significantly the carbon footprint of the production phase of a building, no matter which building system is chosen. Bio-based materials have higher potential environmental benefits for the end-use phase, even as there are uncertainties over the fate of materials in future waste management systems.

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