Technical Booklet E Fire Safety·Page 125·4.48
Flues and heating appliance ventilation ducts penetrating compartment walls and floors
Flues, ducts containing multiple flues, or appliance ventilation ducts passing through or built into compartment walls or floors must have walls of non-combustible construction with fire resistance of not less than half that required for the compartment element.
Where a flue, a duct containing more than one flue, or an appliance ventilation duct –
(a) passes through a compartment floor or compartment wall; or
(b) is built into a compartment wall,
the walls enclosing the flue or duct should have a period of fire resistance of not less than half that required for the compartment wall or compartment floor and be of non-combustible construction, as shown in Diagram 4.12.
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