AHEC_Connected_Stem carbon footprint

Carbon footprint of Stem by Heatherwick Studio

The carbon footprint of the Stem design is 259 kg CO2 eq., about the same as a 2000 km drive and equal to the carbon emissions of the average European over an 11-day period. Total carbon emissions of 563 kg CO2 eq. are offset by 73 kg CO2 eq. due to burning of wood offcuts at Benchmark (which substituted for fossil fuel) and 232 kg CO2 eq. of carbon stored in the wood. It takes only 1.6 seconds for the 320 kg of American maple used to manufacture the Stem design to be replaced by regrowth in the U.S. forest.

Manufacturing of the round and textured planters requires wood sculpturing with a CNC machine which leads to a relatively large amount of waste with only 46% of the wood supplied contained in the finished design. This contributes to a higher carbon footprint than the other Connected designs as there is less carbon storage in the finished product to offset emissions during other life cycle stages. CNC machines also tend to use a lot of electrical power and thereby contribute to a higher carbon footprint. However, this is mitigated in this case by reliance on

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electrical supply from a specialist provider of renewable energy which reduced emissions during manufacturing by 71 kg CO2 eq.

Replacement time of harvested timber

Carbon footprint (Kg of CO2 equivalent)

1.6 seconds

259 Kg

Equivalent distance in a family car (Km)

2026 Km

Equivalent carbon footprint for average European citizen

11 days

Stem is an example of biophilic design which explicitly aims to introduce elements of nature into manmade environments to improve the mental and physical wellbeing of its inhabitants. This aim is important and achieved on many levels by Stem but also creates challenges when calculating the carbon footprint due to the inherent variability of natural materials. While reliable and consistent environmental impact data on U.S. hardwoods is available following AHEC’s investment in independent life cycle assessment (LCA) studies, and due to the existence of accurate forest inventory data in the United States, other natural materials from land-based industries are often more difficult to assess.

The introduction of two Gotland shearlings into the Stem design are a particularly significant area of uncertainty. Emissions of both sheep farming and tanning processes can vary in practice by a factor of 10 or more depending on numerous variables such as country of origin, farming intensity and possible alternate uses of the land, the extent to which livestock are managed respectively for wool, meat or

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skins, and the chemicals used. In the absence of specific data, this carbon footprint assumes emissions of 10 CO2 eq. per fleece. Ironically, due to production in more controlled conditions making assessment of carbon emissions easier, this footprint uses data for a mixed wool-synthetic fibre of EU origin as a surrogate for the natural fleeces. This highlights the importance of other land-based material sectors investing in more comprehensive and product specific LCA.

While the carbon footprint of Stem is higher than the other Connected designs, it is still low for such a timeless design with every likelihood of remaining in use for many years. The exquisite craftsmanship should ensure that no component needs to be replaced and that the carbon remains locked in the furniture and is not released into the atmosphere.

A slight adjustment to the design would also have significant carbon benefits. The glass top and metal fixings add 158 CO2 eq. to the carbon footprint. If the top were made in maple instead, the carbon footprint of the entire design would be reduced to no more than 97 kg CO2 eq. due both to lower emissions and a larger offset due to carbon storage.

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