Leaning Chimney Stacks


Chimney stacks are exposed to some extreme weather conditions, from intense heat, to plummeting cold, chimney’s bear the full force of the countries sun, high winds, rain, frost, and snow which all contribute to weakening the structure. These weather conditions can cause dislodged pots, leaks and leaning of the chimney stack.

What causes chimney stacks to lean?

It is not just the weather than can cause chimney stacks to lean. Burning fuels cause hydroscopic salts which leave the brickwork vulnerable if the chimney is not lined. Salts attract moisture and when these salts dry, they crystallise in the mortar and expand. If your stack is over a century old, it may not be lined. Steel liners should be replaced around every 10 to 15 years to continue protecting the brickwork.

Chimney stacks can also be affected by inadequate alterations. If you have had part of a chimney stack removed, but no gallow bracket or steel beam was used to support the chimney above, then that could cause some instability and movement of the chimney stack.

Are some properties more vulnerable to leaning chimney stacks than others?

Those most at risk are the tall slender flue stacks of the 1930’s.

Victorian properties will have lime mortar joints which are less vulnerable to sulphate attacks compared to the cement mortar joints, which, over time can erode causing falling masonry. Mortar repairs can be carried out by removing 20 to 35mm of the mortar and replacing it with sulphate resistant mortar.

How can leaning chimney stacks be prevented or fixed?

If you have a leaning chimney stack, you can use a steel rod to stop the stack from leaning any further, preventing the stack from collapsing.

Another option may be to remove and rebuild part of the chimney stack. The internal diameter should be 200mm or 185mm for a relined flue or remove the stack in its entirety.

It is difficult to assess the condition of a chimney stack from the ground, but your chimney should stand upright. For help with your chimney stack concerns or any other survey requirements, contact Chris at Mace Davies.