Did you know?
Chimney stacks and their flues are an integral part of the structure of your building, designed to remove combustion gases and assist in natural ventilation. Chimney stacks contribute to the architectural expression of your traditional building and its streetscape.
The chimney ‘stack’ is where the fireplace flues terminate above the roof. Chimney stacks 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) which came into use in the 19th century. 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.
What to look for
- Chimney stack condition
Look for stone erosion and missing pointing. Hot gases, soot and condensation combine to form corrosive acids and over years of use 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 leeching from the flue.
- Chimney stack stability
Look for any lean to the stack generally or stones, including the cope, being out of alignment. As well as instability as a result of erosion, the collapse of the internal bridges can occur weakening the stack. Signs of a chimney starting to fail include fragments of mortar and even stone coming down the chimney shaft and the escape of smoke into loft spaces or through the walls of the chimney stack.
- Chimney pots
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).
- Redundant fixtures
TV aerials, satellite dishes etc 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.
What to do?
Any defects in the physical condition of the chimney should be investigated further by a specialist. 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.