What Happens to a Chimney Stack When You Re-Roof in Pontypridd?

Chimney stacks on older Pontypridd terraces take the full force of valley wind and rain, and they are a common source of leaks. When the roof comes off, the stack is exposed from every side, which lets us see problems that were invisible before. This guide explains the options, from simple repointing to taking the stack down.

What we look at first

Once the old covering is stripped, we examine the stack properly: the brickwork or stone, the mortar joints, the pots, the flaunching on top and the lead around its base. Hairline cracks, loose bricks and crumbling pointing show how much water has been getting in. We also look inside the loft, since damp on the chimney breast often points to a failed flashing or cracked mortar above.

Flashings and lead work

The junction between stack and roof is where most chimney leaks start. Old cement fillets crack away from the brickwork, so we replace them with properly formed lead flashings, including a back gutter on the upslope side so water is carried round the stack. Lead is cut into the mortar joints and dressed carefully over the new covering. It is slow work, but it lasts and stops the repeat leaks that patchwork causes.

Repointing, flaunching and pots

If the stack is basically sound, we repoint worn joints, renew the flaunching that holds the pots, and refit or replace damaged pots. Fresh mortar and flaunching shed water properly and stop rainwater getting into the flue. Where a chimney is still used, we explain what to ask a sweep or heating engineer about, since flue condition is separate from the roof work.

• Loose or cracked bricks replaced like for like
• Pots rebedded or swapped if damaged
• Capped or ventilated flues where no fire is used
• Weathering lead checked at every junction

When to rebuild or remove

If the stack leans, the brickwork is loose or repeated repairs have failed, rebuilding it is usually better than patching. For a chimney no longer used, taking it down below the roof line and making good can remove a regular leak point. Removal affects the chimney breast inside and neighbouring properties on terraces, so it needs agreement and may need planning or Building Regulations checks — we advise before work starts.

Doing it while the scaffold is up

Chimney work is far safer and simpler with the scaffold already in place. Dealing with the stack during the re-roof means the new covering and lead are fitted together, not bolted on afterwards. We talk through the options with you at the survey and photograph the stack before and after, so you can see the actual condition rather than take our word for it.

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