Chimneys take more weather than any other part of a roof. This guide covers the faults we find most often on Oxfordshire stacks and exactly what putting each one right involves.
Why the stack fails before the roof does
A chimney is exposed on four sides, is not protected by a covering, and sits in the wettest, windiest position on the building. It is also the one element that used to get heated from the inside and no longer is, so many stacks are now permanently cold and damp.
Unused flues make this worse. Without warm air moving up the flue, moisture stays in the brickwork and salts migrate into the plaster on the chimney breast inside.
Flaunching, pots and cowls
The flaunching is the sloping mortar cap that holds the pots and sheds water off the top of the stack. It cracks with thermal movement, typically at around 20 to 30 years, and once cracked it funnels water straight into the core of the chimney.
Renewing flaunching means chopping out the old mortar, resetting the pots plumb, and forming a new sloped cap with a drip. If the flue is redundant, a capping cowl keeps rain out while still letting the stack breathe, which is important because sealing a flue completely traps moisture inside.
Brickwork, repointing and rebuilds
Spalled brick faces mean water has entered, frozen and pushed the surface off. Isolated bricks can be cut out and replaced. Where the top few courses have gone, a rebuild above the roof line using the sound bricks below plus matched replacements is the usual answer.
A stack leaning noticeably, or with mortar you can rake out with a finger over most of its height, has moved past repointing. Our chimney repointing cost guide covers the pointing side in detail.
The flashing set at the roof line
Where the stack passes through the roof there should be four separate lead components: a front apron, side soakers with stepped cover flashings, and a back gutter. Cement fillets instead of lead are a shortcut that always cracks.
A back gutter is the piece most often skimped, and it is where the most damaging leaks come from, because water runs down the slope and collects behind the stack with nowhere to go. Renewing a full flashing set is skilled work and it is the repair that solves most chimney damp complaints.
Repair costs and removal as an option
Renewing flaunching and resetting pots typically costs £350 to £700. A full lead flashing set is more often £650 to £1,400. Rebuilding a stack above the roof line generally runs £1,200 to £2,800, and taking a redundant stack down to below roof level and tiling over is usually £900 to £1,800.
Scaffold is a large part of every one of those figures, so if a chimney needs work it is worth checking whether ridge, valley or gutter jobs can be done at the same time.
Should I remove a chimney I never use?
It removes a long term maintenance liability, but it also removes a period feature and needs care with the structure and the breast inside. We price both options and let you decide.
Why is damp appearing on my chimney breast?
Most often a cracked flaunching or a failed flashing letting water into the stack, or hygroscopic salts drawn out of an old flue. The pattern and timing of the damp usually tells us which.
Can a chimney be repaired without scaffolding?
Realistically no. Working on a stack needs a safe platform at ridge height, and a chimney scaffold with a lift around the stack is standard for anything beyond an inspection.
How long does chimney work take?
Flaunching and pot work is usually a day. A flashing set is one to two days. A rebuild above the roof line is generally two to three days once the scaffold is up.
Do I need a liner if I am reopening a fireplace?
Lining is a job for a registered flue installer rather than a roofer. We deal with the external stack, flaunching, pots and flashings, and we will tell you when you need a sweep or flue specialist instead.
Worried about your chimney?
Send us a photograph from the garden and we will tell you what we can see, then come and look properly if it needs it.
Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.