Between the walling cassettes and the external cladding (a composite metal panelling system) is a void, literally a 'breathing space', which provides natural ventilation for the Hemcrete.

在这些墙体盒子和外部保护层(一个复合金属镶板系统)之间是空的，直白地说就是一个“呼吸空间”，给这些Hemcrete提供自然通风。

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The blowtorch caused the ignition of the wood behind the external cladding.

BBC: The damage to the roof

The fire service said the workers tried and failed to extinguish the blaze and it spread behind the external cladding "extremely quickly due to the dry nature of the material".

BBC: The damage to the roof