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Chimney stacks and their flues are an integral part of the structure of traditional buildings, designed to remove combustion gases and assist in natural ventilation. Chimney stacks also contribute to the architectural expression of your traditional building and the wider streetscape. Being in an exposed position, they can start to show signs of disrepair. High level masonry in poor condition can pose a risk to building users and members of the public and issues should always be addressed promptly.
The HES Inform Guide Domestic Flues and Chimneys provides additional information.
The chimney stack is where the fireplace flues terminate above the roof. They may be built of dressed stone, rubble or brick. Chimney flues, constructed within the depth of the external wall, are brought together in the chimney stack and divided by walls known as bridges (or feathers).
Sometimes chimney flues were lined with ceramic liners or are coated with a lime mortar during construction (pargetting). The flue is terminated by a chimney pot (or can). The stack is capped with a cope, the pots being held in place with mortar ‘haunching’ or sometimes set into a rebate in the cope for a more secure fixing.
Pots should be vertical and free from cracks. Haunching should be in good condition and hold the pots firmly. Unused flues should have pots capped with an appropriate flue ventilator allowing adequate ventilation whilst preventing rainwater penetrating (and birds nesting).
Look for stone erosion and missing pointing. Hot gases, soot and condensation combine to form corrosive acids and over years of use and the linings and walls of chimney stacks may have eroded from the inside. The line of a flue is sometimes visible on gable walls where stone has been stained by combustion products leaching from the flue.
Visiting Stonemasonry & Pointing to discover how to spot common problems.
TV aerials, satellite dishes and their fixings can cause movement through wind shear or failure of the masonry as a result of bolts rusting and expanding within the stone. Redundant fixtures should always be removed and those in use should be monitored to check no damage is occurring.
Smoke escaping from a flue could contain carbon monoxide which can cause death. In this case, cease to use your fires immediately and contact a chimney specialist to test the integrity of the flues. Always have a working Carbon Monoxide detector in each room where there is a heating appliance such as an open fire, stove or gas cooker.