The short answer
It can be. A hairline crack in a pot that is firmly bedded is often a slow problem, but a wide crack, a pot that moves, or one leaning to a side can fall in wind. Falling clay is heavy and sharp, so keep people away from the foot of the stack until a roofer has looked.
Why a cracked pot matters
A chimney pot is a clay tube, bedded in mortar at the top of the stack and exposed to everything the weather can throw at it. It carries no load, but it does stand on the highest point of the house with a long drop below. If it breaks, the pieces fall to the roof, the gutter, the garden or the pavement. A whole pot weighs a surprising amount, and a broken section arriving from roof height can injure someone or smash a conservatory roof, a car or a skylight.
A crack also lets water into the pot's wall. In winter that water freezes and expands, widening the crack a little with each cold spell. Over a few seasons a fine line can open into a split that runs the full height of the pot, and the pot can then break apart without warning in a storm.
Cracks that can wait and cracks that cannot
| What you see | How urgent |
|---|---|
| Fine vertical hairline, pot firmly bedded | Not urgent; photograph it and check it again after winter |
| Crack with a visible gap, or a spalled outer face | Soon; the pot is failing and should be replaced |
| Crack running right round the pot | Urgent; the top section may fall |
| Pot leaning or rocking in its bed | Urgent; the bedding has failed as well |
| Pieces already on the roof or in the gutter | Urgent; the pot is breaking up now |
The pot is only one part of the picture. Often the real fault is the flaunching, the mortar collar around the pots, which has cracked and let water in. Our page on chimney flaunching describes it. Replacing a pot without redoing the flaunching only treats half the problem.
What to do straight away
- Keep people, children and pets away from the area directly below the stack, including the pavement if the house fronts the road.
- Do not climb up or lean a ladder against the stack. A pot that looks sound can come away in your hand.
- Take photographs from the ground with a zoom lens, or ask a roofer to use a drone, so there is a record of the crack and its position.
- If the pot is already loose or pieces have fallen, call a roofer to make it safe. A roofer can lift off a failing pot and cover the flue temporarily.
- Book a proper repair once the immediate danger has passed, rather than leaving the temporary fix for months.
If the stack has been hit by a storm and you plan to claim, take your photographs before anything is moved. Our page on whether insurance covers chimney repairs explains how claims tend to be judged.
How a cracked pot is put right
The fix depends on how bad the damage is. A cracked pot that is otherwise sound can be replaced like for like. The roofer breaks the flaunching, lifts the pot, checks the top courses of the stack for looseness, and beds a new pot in fresh mortar. A new collar is formed in a smooth slope that sheds rain. If the crack is minor and the flaunching is the problem, the work may be limited to repairing the flaunching and watching the pot. Where the brickwork around the pots is loose or the stack top is wearing out, the work widens to repointing or rebuilding the top courses, which we explain in chimney pots and cowls.
Replacing a pot on a period house may mean matching the style. Where the house is listed or sits in a conservation area, check with the council's conservation officer before changing the look of the stack. A like-for-like replacement is usually fine, but ask first.
What it costs, and how to avoid a repeat
Access is often the largest part of the cost, because a safe working platform has to be provided at the stack. Our page on how much it costs to replace a chimney pot goes through the figures. Cost guides give chimney repair as a whole a wide range, from £500 up to £2,000, with an average near £750, and the price for your stack follows the survey.
To avoid a repeat, have the stack looked at every few years. A quick check of the flaunching, the pot bedding and the joints at the top costs little and catches a failing pot before it drops. Fitting a cowl or cap at the same time protects the clay from direct rain. Start from the main chimney repairs page if you want an overview of the work we do.
Every roof is different. A free survey with photos settles it for yours.
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