How to ensure your chimney is constructed correctly

Virtually every building or home has at least one chimney, so making sure it is built properly is essential to allow safe ventilation without causing damage to the structure. Here are some top tips on how to construct your chimney.

Chimneys must be constructed so that its height is no greater than four and a half times its smallest width. This should be measured from the level of the highest point in line with the roof.

The diagram below shows the correct provision of flashings.

Flues and linings

Flues work with any construction type and must maintain as high a temperature as possible. It is essential to:

  • Fill all joints with jointing and caulking material in accordance with the manufacturer’s instructions.
  • Build socketed flue liners with the inner surface of the lining smooth at the joints and socket ends uppermost, if necessary.
  • Fill the void between brick chimneys and clay or concrete flue liners with lightweight concrete or weak mortar.
  • Do not use cracked or broken liner sections. Form bends with purpose made fittings.

Extend lead or proprietary horizontal DPC trays through the liner into the flue and turn upwards – see below diagram:

The construction of flashings is dictated by the type of roof tile/cladding to be installed. Please refer to the roof tile /cladding manufacturer’s details for specific flashing detailing.

For more information on Chimneys and Flues refer to chapter 7 of our Technical Manual

By Olivia Catterall

Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.

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