Chimney wall thickness and construction
100 mm
The minimum wall thickness for block, brick, or stone chimneys, excluding flue lining, is typically 100mm
The minimum wall thickness for block, brick, or stone chimneys, excluding flue lining, is typically 100mm. Where chimneys form part of a compartment wall or separate dwellings, specific wall thicknesses apply to ensure fire resistance and separation. Factory-made insulated chimneys must adhere strictly to manufacturer's installation guidelines.
Basis in regulation
How to check it on site
Check the thickness of chimney walls, ensuring 100mm minimum for general construction, and 200mm for compartment walls, and verify factory-made flues are installed per manufacturer's instructions.
Common failure
Insufficient wall thickness in masonry chimneys, or incorrect installation of factory-made flues, compromising fire safety.
Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.