Practice Note for Authorized Persons,

Buildings Department Registered Structural Engineers and APP-8

Registered Geotechnical Engineers

Chimneys and Flues

The design and construction of a chimney and a flue should comply with
the requirements in section 44 of the Building (Construction) Regulation (B(C)R). This
practice note sets out the detailed design requirements for the attention of the authorized
persons and registered structural engineers.

Fire Safety and Heat Transmission

2. A chimney or a flue should be constructed of non-combustible materials

of such a nature, quality and thickness so that it will not be unduly affected by heat,
condensation or products of combustion. Its design and construction including the
position where it terminates should comply with the fire safety requirements set out in
section 44(2) to (4) of the B(C)R.

3. The insulation required for a chimney or a flue depends on various factors

viz. the type and rate of fuel used, the materials of the nearby parts of the building and
the use of the surrounding areas. Calculations and justification should be provided in
each case to verify compliance with the B(C)R. In this connection, BS 5854:1980
provides some guidelines.

Structural Design

4. The structural design of a steel chimney should be in accordance with the

Code of Practice for the Structural Use of Steel 2011 (Steel Code) and in particular, the
guidance given in Clause 13.2 of the Steel Code. Special attention should be given to
the wind-excited oscillations which should be considered and analysed by aerodynamic
methods so that suitable provisions are made to control the oscillations. For circular
chimneys, the simplified method in Clause 13.2.8 of the Steel Code may be adopted.

Construction and Corrosion Protection

5. For construction and corrosion protection of chimneys and flues, the

relevant parts of the Steel Code, BS EN 1856-1:2009 and BS 5854:1980 should be
followed. Attention should be given to the following:

Corrosion protection and bimetallic action

(a) Guidance on corrosion protection and avoidance of bimetallic

action of a steel chimney are given in Clause 13.2.7 of the Steel
Code. Appropriate protective treatments on the interior and
exterior surfaces of a steel chimney or a flue should be provided
in accordance with the manufacturer’s instructions and the
acceptable standards in Annex A of the Steel Code.

/Opening …
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Opening for a chimney or a flue

(b) At the point where a chimney or a flue penetrates the wall or

roof of a building, suitable flashing or weather hood taking into
account different co-efficients of expansion and bimetallic
action should be provided.

Other Considerations

6. Installation or alteration of flue-burning equipment and/or its chimney on

premises are subject to the control of the Air Pollution Control Ordinance. Prior
approval from the Environmental Protection Department (EPD) may be required.
Pursuant to Practice Note for Authorized Persons, Registered Structural Engineers and
Registered Geotechnical Engineers ADM-2, general building plans involving installation
of chimneys or flues will be referred to EPD for comments under the centralised
processing system. Similar installation or alteration in relation to food business or
offensive trade licence application should meet the relevant licensing requirements.

( YU Tak-cheung )
Building Authority

Ref. : BD GP/BREG/C/12/A

This PNAP is previously known as PNAP 45

First issue September 1977
Last revision July 1994
This revision May 2021 (AD/NB1 & AD/NB2) (General revision and Appendix A
deleted)