Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 90·B.11
Distance to combustible material
The minimum distance from the outer surface of the chimney to combustible material is designated in millimetres, with specific examples referenced in other sections.
The designation of the minimum distance from the outer surface of the chimney to combustible material is given as xx expressed in millimetres (e.g. the distance 'XX' identified in paragraph 2.37 and Diagram 2.5).
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet L - Combustion Appliances and Fuel Storage Systems.pdf