Does My Chimney Need Rebuilding or Just Repairing?

Most chimneys only need repointing, new flaunching or fresh flashing. Some need rebuilding. Here is how to tell the difference and what each involves.

If the stack is straight and the bricks or stones are sound, repair is almost always enough: repointing, new flaunching around the pots and new lead flashing where it meets the roof. A rebuild is needed when the stack is leaning, the masonry itself is breaking up, or the mortar has failed so deeply that the stack is no longer holding together.

Rebuilding is a bigger job, so a good roofer will only recommend it when repair would not make the chimney safe.

Mortar that has eroded back from the face of the joints, cracked flaunching on top of the stack, a damp patch on a chimney breast after rain, and lifted or split flashing are all common and all repairable. Repointing replaces the worn outer mortar, new flaunching sheds water off the top, and new flashing seals the junction with the roof.

Our chimney repair and repointing guides cover these jobs in detail.

Signs a rebuild is needed

A visible lean is the clearest sign, often caused by sulphates from years of flue gases attacking the mortar on one side so it expands. Bricks that are spalling, cracked right through or loose enough to move, stones that have split, deep cracks running through the stack rather than just the joints, and a stack that has been patched so many times there is little original sound work left are others.

A leaning or loose chimney is a safety concern because of the weight of masonry above the roof. If you notice one, keep people away from underneath and get it checked promptly.

Often only the section above the roof line needs rebuilding, and sometimes only the top few courses. The stack is taken down carefully to sound masonry, then rebuilt with new or reclaimed materials, new flaunching and new flashing. A full rebuild down through the roof is less common and usually linked to serious structural movement.

When a chimney is no longer used, removing the stack above the roof is sometimes discussed. In conservation areas and on listed buildings, the chimney may be an important part of the building's character and permission may be needed before altering it.

On older homes, a rebuilt stack should match the rest of the house. That means sourcing bricks or stone that match in colour and size, and using a mortar that suits the masonry. Traditional brick and stone chimneys often need lime mortar, which allows moisture to escape rather than trapping it in the masonry.

Pots can usually be reused, and the chance is often taken to fit cowls or caps on flues that are no longer used, to keep rain and birds out while allowing ventilation.

It helps to note when you first noticed the problem, whether the fireplace below is still used, and whether any damp appears inside after rain. Photos of the stack from the ground or from a neighbour's garden are useful too. None of this replaces an inspection from close up, but it helps a roofer understand the history of the chimney and plan the right access for the visit.

Chimney work needs safe access, normally a scaffold with a platform around the stack. Masonry is taken down by hand, materials are lowered safely, and the rebuild is done course by course before the flaunching and lead flashing are completed. Surrounding tiles or slates disturbed by the work are made good at the end.

Why is my chimney leaning?

Often sulphate attack from flue gases has expanded the mortar on one side over many years. Wind exposure and movement can contribute.

Is a leaning chimney dangerous?

It can be, because of the weight of masonry above the roof. Keep people clear below and have it inspected promptly.

Can you rebuild only the top of a chimney?

Yes. The stack is taken down to sound masonry, which is often just the section above the roof or the top few courses, and rebuilt from there.

Will a rebuilt chimney match my house?

It should. We match bricks or stone and use mortar suited to the masonry, including lime mortar on traditional chimneys.

Do you also repoint and reflash chimneys?

Yes. Repointing, flaunching, lead flashing, cowl fitting and stack rebuilds are all part of our chimney work.

Worried about your chimney stack?

We will look at it properly and tell you whether it needs repair or rebuilding, with the reasons set out in a written quote.

Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.