The short answer
Call a chimney sweep when the problem is inside the flue: soot, smoke coming back into the room, a nest, or a stove or fire that needs clearing before use. Call a roofer when the problem is the stack itself: loose pots, crumbling brick, failed pointing, flaunching or flashing, or a leak. Often both are needed, and the sweep goes first so the roofer can see inside.
What a sweep does
A sweep works on the inside of the flue. Brushes and rods remove soot and tar from the walls, and a sweep clears debris, nests and fallen mortar. Many will inspect the flue with a camera and check that smoke is drawing properly. The job is done from the room, with sheets over the hearth.
You would normally call a sweep if smoke comes into the room, a fire burns poorly, there is a smell of soot, or birds are heard in the chimney. Sweeping before the heating season is routine for any flue that is used. Our answer on how to tell if your chimney is blocked lists the signs that point to the flue.
What a sweep does not do is mend masonry. A sweep may tell you the flue is damaged, which is useful, but the repair is a builder's or roofer's job.
A sweep can also tell you whether a flue is suited to the appliance you want to burn in it, and will usually issue a certificate you can show an insurer or a buyer. Questions about burners and fuels belong with the sweep or the installer.
What a roofer does
A roofer works on the outside, at the point where a stack meets the roof. That means everything you can see from the garden and a good deal you cannot:
- repointing the brick or stone, and replacing bricks that have spalled
- re-bedding pots in new flaunching, the mortar cap that holds them
- fitting or replacing lead flashing, soakers and back gutters
- capping or ventilating an unused flue
- rebuilding part or all of a stack that has leaned or cracked
Working at height needs scaffold or a proper platform for any job beyond the simplest, and the cost of that access is part of the quote. A roofer can also explain how a stack relates to the roof around it, from the tiles and verge to the ridge, which is why a leak that shows indoors near the breast is a roofer's question first.
Symptoms and who they point to
The table sets out the usual pairings. They are a starting point, since a single fault can have more than one cause.
| What you notice | First call | Why |
|---|---|---|
| Smoke or fumes in the room | Sweep | A blocked or smoking flue is an internal fault |
| Soot falling into the hearth | Sweep | Deposits need brushing out |
| Stain on the ceiling by the breast | Roofer | Usually water entering at flashing or flaunching |
| Crumbling bricks or open joints | Roofer | The stack's masonry needs repair |
| Pot loose or missing | Roofer | Set in mortar on the very top of the stack |
If you are unsure, start with whichever symptom is loudest and say what else you have noticed. A good sweep will tell you if the flue itself is sound, and a roofer will say if the flue needs checking first.
One case catches people out. Rain falling straight down an uncapped flue can run into the grate and look like a leak, yet no roofer will find a defect in the lead. A cowl or cap is a roofer's fix, and a sweep will often be the one to notice the wet soot that shows it is happening.
When you need both, and in which order
Some jobs need the two trades one after the other. A stack with a damaged pot and a flue full of debris is the common example: the roofer replaces the pot and flaunching, while the sweep clears what has fallen down the flue. Before a roofer rebuilds or lowers a stack, a sweep's camera survey can show cracks inside the liner that would change the plan. After the repair, the flue is swept again, so it is clear before it is used.
If a stove is going in, the liner, the cowl and the stack all have to be considered together. We cover the roof side of that, not the appliance. Where you do not use a flue at all, a roofer can cap it, usually with a vented cap so air still moves through; our guide to capping a chimney explains how.
It also helps to know how long a repair might take before you book a sweep around it. Our answer on how long a chimney repair takes sets out what affects the timing, and our note on a stack whose breast has been removed shows a case where the order matters.
Asking for the right survey
When you contact us about a chimney, describe what you see and where. Photographs of the stack from the garden, and of the ceiling and breast inside, are very useful. Tell us whether the fireplace is used, and when the flue was last swept, if you know. Our survey records the stack and the roof in photographs, and the written quote ties back to those pictures, so nothing in it is a mystery to you.
If the problem is plainly inside the flue, we will say so and suggest a sweep first, because repairing masonry above a blocked flue wastes money. Repairs we carry out come with a 10-year workmanship guarantee, put in writing, and we remove our own waste. The other chimney jobs we handle are set out on our chimney repairs page.