Signs your chimney needs repair

Stand back far enough to see the whole stack on a bright day; a phone camera zoomed in helps. The Society for the Protection of Ancient Buildings says chimney mortar weathers fastest at the top of the stack, on the side facing the prevailing wind, and at or just below the roof line (SPAB, chimney maintenance), so look hardest there.

• Pointing worn back: joints sitting deep behind the brick faces, or gaps where mortar has gone.
• Cracked flaunching: the sloped mortar on top that holds the pots, cracked or broken away.
• A loose or leaning pot: pots stand in that mortar, so they loosen as it fails.
• Flaking bricks: faces that have blown off, often near the top.
• Plants on top: SPAB notes weed growth can be a symptom of weathering.
• Flashing lifted or split: the strip sealing the joint between stack and tiles.

A chimney often shows its problems indoors first. Look for:

• a damp patch or brown tide marks on the chimney breast, often high up;
• paint bubbling or wallpaper lifting on the breast;
• damp timbers or stained felt beside the stack in the loft;
• grit or mortar crumbs falling into a fireplace;
• smoke coming back into the room from a fire that used to draw well.

Damp on a chimney breast can come from rain soaking through worn brickwork, water getting past the flashing, rain down an open flue, or a blocked-off flue with no ventilation. If water is actually dripping, see what to do when your roof is leaking.

A chimney stack stands clear of the roof, so it takes wind and rain on every side. Once rain soaks into worn joints, frost pushes the mortar out further each winter. SPAB says eroded mortar in a chimney "can lead to smokiness, dampness, increased fire risk and instability".

The repair has to suit the bricks. On older houses, SPAB advises that repointing mortar should normally be lime-based, without cement: hard cement pointing traps water, and the soft brick faces crumble instead of the joints. If an old repair used grey cement and the bricks around it are flaking, that's why. How repointing, flaunching and flashing repairs are done is on my chimney repairs page.

Most chimney wear is slow: worn pointing or a small crack in the flaunching can wait for a visit, though not for years. Some signs need action straight away.

Call me any time, day or night, if:

• a pot is loose, has fallen or is leaning after high winds;
• the stack itself is leaning or has a crack running through it;
• water is coming through the ceiling beside the chimney breast.

Keep people and cars away from below a loose pot until it's made safe.

Not a roofer's job: smoke or fumes coming into the room, or a gas fire or boiler flue you're worried about. Carbon monoxide has no colour or smell, so the NHS advises stopping using an appliance you think might be making it (NHS, carbon monoxide poisoning). Call a Gas Safe registered engineer or a chimney sweep.

Many Oxford houses have more flues than fires: a 1930s semi in Headington or Cowley often shares a stack with next door, and a Victorian terrace in East Oxford can carry several pots, most long out of use. An unused chimney still weathers, and nothing shows inside until damp appears.

SPAB says a disused flue can be capped after sweeping, as long as some ventilation is kept. If you'll never use the chimney again, taking the stack down below the roof line and tiling over it ends the upkeep. If it's shared with next door, or the house is listed or in a conservation area, check the rules first: see my guide to listed building roof repairs.

I check the pots and flaunching, the pointing on every face of the stack, the brickwork, and the flashing where the stack meets the tiles. Then I tell you plainly what it needs and give you a free written quote. I usually come the next day, and the visit is free.

I repoint stacks, renew flaunching and lead flashing, fit cowls and take down stacks you no longer use, with lime mortar on old stone and soft-brick chimneys. Chimney repairs come with a written guarantee of at least 5 years.