Chimney Cracks & Leaks
Chimneys take the weather full-on for 100+ years — and they show it before the rest of the house does.
Chimney leaks and cracks are almost always caused by weathered mortar, failed flashing at the roof junction, or a missing chimney cap. Older Federation and Interwar chimneys across Sydney need repointing every 40–60 years. A leaning chimney or one with loose bricks can be dangerous in strong wind. Proper repair includes repointing with matched lime mortar, replacing lead flashings, and fitting a chimney cap — if it is beyond saving, partial or full rebuild is the honest answer. Romans Building Services assesses chimney cracks & leaks across Sydney before recommending repair, so the visible damage and the cause are both dealt with.
Last updated: 2026-05-29
What is chimney cracks & leaks?
Chimneys sit up above the roof line taking everything the weather throws at them — sun, rain, wind, salt in coastal areas — with no protection from the rest of the building. They crack, lean, lose their mortar, and their flashings fail. A lot of the old Federation and Interwar chimneys across Mosman, Woollahra, Strathfield and similar suburbs are now 80+ years into their life and showing it.
A leaking chimney usually shows up as water stains on ceilings near the flue, damp patches around the fireplace, or rust stains on the external brickwork. Those stains are often weeks or months of water damage inside the roof space before they appear. The fix is rarely just patching the leak — it usually involves repointing, re-flashing, sometimes rebuilding the top section.
Leaning chimneys are more serious. They can be caused by foundation movement, rusting steel inside the brickwork, or decades of weather eroding the mortar on one side more than the other. A chimney that has lost its plumb is a chimney that can eventually fall — especially in strong wind.
Signs to look for
- Water stains on ceilings near the flue
- Damp patches inside the fireplace or around it
- Rust stains running down the external brickwork
- Mortar crumbling or missing from chimney joints
- Chimney visibly leaning out of vertical
- Bricks loose at the top of the chimney
- Flashing around the base torn, lifted or damaged
- White salt deposits (efflorescence) on the brickwork
Why it happens
- Failed or damaged flashing at the roof junction
- Mortar weathered out — most common on older chimneys
- Rusting steel cramps or ties inside the chimney expanding
- Original flue unlined or liner degraded
- Chimney cap missing, allowing water straight in
- Tree impact or high wind damage
- Foundation movement pulling the chimney base out of plumb
How urgent is this?
A leaning chimney or one with visibly loose bricks is dangerous — in a storm it can fall and do serious damage. Leaks are less urgent but cause accelerating internal damage if left. If you can see bricks moving, the flashing is lifted, or water is entering, it needs attention.
How we fix it properly
Safe access and inspection
Scaffold or edge protection for safe access. We inspect the full chimney — mortar joints, flue condition, flashing, cap, bricks. Often internal access to check the flue from inside is also needed.
Repoint failing mortar
Rake out failing joints and repoint with matched mortar. For heritage chimneys, lime mortar. We pay extra attention to the top few courses, which take the worst weather.
Replace loose or damaged bricks
Any bricks that are loose, cracked or missing get cut out and replaced. Matched handmade or pressed bricks depending on the chimney age. The top 2–4 courses sometimes need full rebuild.
Re-flash properly
Lead flashings at the roof junction — base, step, and over-flashing. This is where most chimney leaks come from. Done properly with lead dressed into the mortar joints, it lasts as long as the chimney.
Install a chimney cap
If there is no cap, we fit one — a proper chimney cap keeps water out, stops birds nesting in the flue, and improves draught. Small job, big impact on chimney life.
Straighten if leaning
For a leaning chimney past saving, partial or full rebuild with reinforced core and new flashings. For chimneys with minor lean but sound fabric, tie-backs to the roof structure can stabilise.
Typical cost range
Repointing and re-flashing typically $3,500 – $8,500. Top-section rebuild $6,000 – $12,000. Full chimney rebuild $15,000 – $30,000+ depending on height and access.
Every job is different. We give a firm quote after inspection.
Common questions
My chimney is leaking but I have not had a fire in it for years. Do I still need to fix it?
Yes. The leak is water getting into your roof space and eventually your ceilings. It does not matter whether the chimney is in use — the damage is the same. And if the chimney is decommissioned, consider getting it capped off properly so it stops being a maintenance item.
Can I keep using the chimney after repairs?
If the flue is sound or has been re-lined, yes. If the flue is degraded, we recommend re-lining or decommissioning for wood-burning use. Gas fires have different requirements — usually need a flexible flue liner.
How long do chimney repairs last?
Proper repointing with appropriate mortar: 40–60 years. Lead flashings: 50+ years if installed correctly. Full rebuild: same life as the original chimney, typically 100+ years. Cheap short-cut repairs often fail in 5–10 years.
Can you remove a chimney that is beyond saving?
Yes. Chimney removal, flue capping, internal make-good and roof patching. Often a cleaner solution for decommissioned chimneys that are failing. We'll tell you honestly whether yours is worth saving or whether removal is the right call.
Services that fix this
Where we see chimney cracks & leaks most often
Some suburbs have more of this problem than others — the local housing stock, age, and coastal exposure all play a part. Click through for the local context.
Think you might have chimney cracks & leaks?
Send a photo or call Minas directly. We will tell you straight whether it needs doing now, or whether it can wait.