Chimneys: Common Problems in older buildings
How chimneys work in traditional properties
Chimney stacks and their flues are an integral part of the structure of your traditional property, designed to remove combustion gases and assist in natural ventilation. Chimney stacks contribute to the architectural expression of your traditional building and its streetscape. Knowing how to recognise common chimney problems on older buildings is essential for providing the right care and repair.
Traditional chimney construction
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 common 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.
Common chimney problems on older buildings
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 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 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.
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).
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.
What you can do about chimney problems on your older building.
Any defects in the physical condition of the chimney should be investigated further by a specialist - for example, a skilled stonemason for construction issues, or a chimney sweep to undertake cleaning of the flue. 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.