What the job involves
A chimney stack takes a beating. It sits at the highest, most exposed point of the house, with weather hitting it from every side. Most repairs fall into a few familiar categories, and a single visit often covers more than one.
Repointing. Old mortar between the bricks or stone crumbles over time. The loose material is raked out and the joints are refilled with fresh mortar. On older homes the mortar should usually be a softer, lime-based mix rather than hard modern cement, which can damage soft bricks.
Flashing and lead work. Flashing is the waterproof strip, normally lead, where the stack meets the roof. It generally includes an apron at the front, step flashings up the sides, and a back gutter behind the stack to carry water round it. Cracked, lifted or badly dressed lead is one of the commonest causes of damp patches on chimney breast walls and ceilings.
Flaunching and pots. The flaunching is the sloping mortar on top of the stack that holds the pots in place and sheds water. When it cracks, rain gets into the flues and the brickwork. Repairs can mean re-bedding pots, replacing the flaunching, or fitting cowls or caps.
Brickwork repairs. Spalled or frost-damaged bricks can be cut out and replaced. If the top courses are loose or the stack leans, the sensible fix may be taking it down and rebuilding to a safe height.
The usual scope for this type of job is repairs to one stack. The details depend on what the roofer finds once they can see it properly, which is rarely possible from the ground.
What affects the price
- Access and scaffolding. This is often the biggest single variable. A low stack on a bungalow may be reached with a ladder and roof ladder, or a small scaffold tower. A tall stack on a three-storey house usually needs full scaffolding, which adds cost for erection, hire and removal.
- Where the stack sits. A stack at the ridge is usually simpler than one on a slope or at the gable end. A steep or complex roof means slower, more careful work.
- How much needs doing. Repointing a few joints is a different job from repointing the whole stack. Replacing flashing is different again from patching it. The more areas involved, the more labour and materials.
- Condition of the brickwork. If the bricks themselves are crumbling, repointing alone will not last. Replacement bricks or a partial rebuild add time and materials.
- Lead work. Lead is a premium material and its price moves. More flashing, wider lead, and detailed work such as a back gutter all increase cost. Proper lead work is skilled, and it is priced accordingly.
- Materials matching. Matching old bricks, or using lime mortar on a period property, costs more than standard materials.
- Flue condition and use. Rebuilding a stack, fitting liners, or capping and ventilating a redundant flue each add to the scope.
- Shared stacks. If the stack is shared with a neighbour, there may be extra coordination, and the Party Wall etc. Act may be relevant for some types of work.
- Location and demand. Labour rates vary by region, and good roofers are often booked weeks ahead.
- Listed or conservation area properties. Approved materials and methods, and sometimes consent, can add both cost and time.
Ways to keep the cost down
- Deal with problems early. A small flashing fault or patch of failed pointing is cheaper than repairing the water damage that follows.
- Combine work with other roof jobs. If the roof needs other repairs, having them done together means paying for scaffolding once.
- Share scaffolding. If a neighbour needs chimney or roof work, ask whether the scaffold could be shared.
- Get several quotes for the same scope. Ask each roofer to price the same list of tasks so you can compare like with like.
- Ask for a photo report. A roofer who photographs the problems from the stack can show you exactly what needs doing and what could wait.
- Be flexible on timing. Some roofers are quieter in certain seasons and may fit you in more readily.
- Do not cut corners on lead or mortar. Cheap materials usually fail early, and you pay for scaffolding all over again.
What should be included in a quote
A proper quote should be in writing and specific. Check it covers:
- [ ] The exact repairs listed: repointing, flashing, flaunching, pots, brick replacement, and so on
- [ ] The extent of each repair, such as the whole stack or specific faces
- [ ] Access arrangements, including whether scaffolding or a tower is included and who arranges it
- [ ] Materials: mortar type, lead thickness or code, and brick matching
- [ ] Removal and disposal of rubble and old lead
- [ ] Protection of the roof and garden, and clearing up afterwards
- [ ] What happens if extra problems are found, and how any additional work is agreed and priced
- [ ] Whether VAT is included
- [ ] Start date, expected duration and payment terms
- [ ] Guarantee details, in writing, with what they cover and for how long
- [ ] Evidence of public liability insurance
Questions to ask a roofer
- Can you show me photos of the problem areas before you start?
- Is the existing mortar lime or cement, and what will you use?
- Is the flashing being replaced or repaired, and why?
- How will you reach the stack, and is access included in the price?
- Does the stack need rebuilding, or will repairs last?
- Is the flue still in use? If it serves a gas appliance, would a Gas Safe registered engineer need to check anything? For solid fuel, should the flue be swept or inspected?
- Will you leave any redundant flues ventilated rather than sealed?
- Do you carry insurance, and can I see the certificate?
- What guarantee do you give, and is it in writing?
- Who will actually do the work: you, employees or subcontractors?
How long it takes and what to expect
For one stack, most repairs take a matter of days rather than weeks. Small jobs such as a section of flashing or some repointing can be done quickly. Scaffolding often needs to go up before work starts and come down afterwards, so allow for that on either side. A full rebuild takes longer, and mortar needs time to cure, so wet weather can cause delays.
Expect noise from raking out joints, and some dust and debris. A good roofer will protect the roof and clear up, and should tell you before taking down any section of the stack.
Once finished, ask for photos of the completed work. Check inside the house over the next few heavy rainfalls for any returning damp. A fresh patch means the problem was not fully solved, so contact the roofer promptly with your guarantee in hand.
Signs a quote is too cheap or too expensive
Warning signs of a quote that is too cheap:
- No written breakdown, only a single vague figure
- No allowance for access, which can lead to a surprise charge later
- Mention of cement mortar on an old property, or plain mortar patching over flashing faults
- Pressure to accept on the day, or a cold call about problems spotted from the street
- A request for full payment up front
- Reluctance to provide insurance details or a written guarantee
Signs a quote may be too high:
- Full rebuild proposed when only repointing or flashing seems needed, with no photos to justify it
- Scaffolding charged for a low stack that is easily reached
- Large allowances for contingencies without explanation
- Far above other quotes for the same scope, with no clear reason
The best check is to compare your quote against the prices on this page, then ask the roofer to explain any gap. A good tradesperson will be happy to talk through the work.