TGD J 2014 – 3.10.2 – Hearths

3.10.2 In the case of a back boiler, the hearth should be constructed: (a) of solid, non-combustible material at least: (i) 125 mm thick, or (ii) 25 mm thick placed on noncombustible supports at least 25 mm high, and (b) to the size given in Diagram 18.

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