The short answer
Call a sweep for anything inside the flue: soot, tar, a blocked or smoking fireplace, a nest, or a flue that needs checking before you burn fuel. Call a roofer for anything on the outside of the stack: loose pointing, a cracked pot, failed flaunching, lead flashing, a leaning stack or a leak that shows on the ceiling beside the chimney breast.
What a sweep deals with
A sweep works from the fireplace and the flue. The job is to clear soot and tar from the inside of the flue, remove blockages such as nests or fallen debris, and confirm the flue draws properly. Many will also run a smoke test, which shows whether smoke is leaking out of the flue into the house or a neighbouring property.
A flue that is regularly used needs sweeping before it is lit for the season. How often depends on the fuel: wood and coal leave more deposit than gas, and wood burned wet or smouldering leaves the most tar. A sweep will also tell you if the flue lining looks cracked or the pot is blocked.
Typical sweep jobs include a fireplace that smokes back into the room, a fire that will not draw, soot falling into the grate, a smell of tar in damp weather and a bird or jackdaw nest dropping down the flue. The inside of the flue is their ground, and it is not work for a roofer.
What a roofer deals with
A roofer works on the stack and the roof around it. That means everything you can see from the street above the ridge line, plus the point where the masonry meets the slates or tiles. Typical jobs are repointing the stack, rebuilding loose courses, renewing the flaunching round the pots, replacing a damaged pot, fitting a cowl or bird guard, capping a disused flue, and replacing the lead flashing and soakers where the stack comes through the roof.
The fault that usually brings a roofer in is water. A damp patch or stain on an upstairs ceiling next to the breast, wet in the loft near the stack, or a breast that goes damp after rain all point to the outside. Our page on chimney repairs sets out the full range, and the lead details are covered under chimney flashings.
A roofer also handles structural signs, such as a lean or a crack that follows the joints. Those need scaffold and a proper look, and are not something a sweep is equipped to assess.
Which problem goes to which trade
Some faults are obvious, and a few are less so. This table sets out the common ones.
| What you notice | Usually the job of | Why |
|---|---|---|
| Smoke coming back into the room | Sweep | A blocked or restricted flue is the first thing to rule out |
| Soot falling into the grate | Sweep | Deposit or debris is coming down the flue |
| Ceiling stain beside the breast | Roofer | Water is entering at the stack, flashing or roof |
| Crumbling mortar or a leaning stack | Roofer | The masonry above the roof is failing |
| Brown staining on the breast | Either, then both | It may be flue tar or rain, so both need checking |
| Bird nest in the pot | Sweep, then roofer | The sweep clears it, the roofer fits a guard |
Staining is the case that confuses people most, and the separate answer on brown tar marks on a breast shows how to tell the causes apart.
Faults that need both trades, and the right order
Some problems sit across the line. A blocked flue caused by a nest needs the nest cleared by a sweep and a guard fitted by a roofer, or the birds return. A flue that has been damaged by years of tar or acid condensation may be found by a sweep and need repair or a liner, with the stack work done by a roofer.
Order matters on a repair. If the stack is being repointed or rebuilt, debris and mortar droppings often fall down the flue. A sweep after the stack work clears them and gives you a clean flue to start with. If a sweep finds a damaged stack on a first visit, the roofer should look before any fire is lit, since a stack that is cracked or leaning is not something to burn under.
It also helps to tell each trade about the other. A sweep who has seen a crumbling pot can describe it for the roofer, and a roofer who has found a blocked pot can tell the sweep what to expect. Fit a carbon monoxide alarm if you burn any fuel, whichever trade you call.
How we approach a stack problem
We are roofers, so our side of the problem is the stack, the pots, the lead and the roof around them. When a call begins with smoke in the room or soot in the grate, we will tell you openly that the flue is the first place to look, and that a sweep is the person to see. If the sweep then finds a problem at the top, we can take it from there.
For stack faults, the free survey gives you photographs of your own chimney, with the pointing, pot and lead pictured close up. Our written price is fixed after that. A stack serving two houses brings in a neighbour as well, and the page on who is responsible for a shared chimney stack deals with that.
An active leak comes ahead of routine jobs, and the roof is made watertight before anything else. If the sweep has already noted cracked pots, loose flaunching or damp in the flue, pass those notes on, since they help us look at the right part of the stack first and save a second trip up the ladder.
