Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 31·2.39
Flue routing restrictions
Flues must not pass through other premises where inspection access may not be available, but may pass through communal areas and purpose-designed ducts with inspection access provided.
Flues should not pass through another premises since access for inspection may not always be available to that premises and chimney system running through it. Flues may pass through communal areas including purpose-designed ducts where inspection access is provided.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet L - Combustion Appliances and Fuel Storage Systems.pdf