Short supply chains, long-lived buildings

Transport is usually treated as a rounding error in embodied carbon. On bio-based assemblies it is not: low-density feedstock fills a truck by volume long before it reaches weight limits, so distance is expensive per kilogram of material delivered.

Restricting reed and straw sourcing to a 180 km radius cut project transport emissions by a further 6% and, unexpectedly, shortened lead times by nine days because harvest scheduling could be coordinated directly with growers.

The counter-argument is resilience: a 180 km catchment is one bad harvest away from a stoppage. The current answer is two overlapping catchments and a six-month fibre buffer, which carries its own storage cost.

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