Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 43·3.15
Protection of combustible materials from flue pipes
Flue pipes must be positioned to prevent ignition of combustible materials, either by using factory-made metal chimneys meeting specific standards or by providing shielding with minimum air gaps and separation distances as shown in Diagram 3.3.
A flue pipe should be located so that it cannot ignite any combustible material. To ensure this –
(a) follow the guidance in paragraph 2.37 where the connecting flue pipe is a factory-made metal chimney whose performance is at least equal to designation T400 N2 D3 G according to BS EN 1856: 1 or BS EN 1856: 2, and installed to BS EN 15287: 1; or
(b) provide separation by shielding in accordance with Diagram 3.3.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet L - Combustion Appliances and Fuel Storage Systems.pdf