What Causes Water to Enter Around Chimneys?

The Routes, Quickly

Water gets into a chimney at the flaunching on top, through eroded pointing, through spalled brickwork on the weather face, through any of the four pieces of lead around it, or down an open flue. That is the standard list and the main roof repair advice covers it.

This page is about the one that is not on the standard list, and that is the reason a great many terrace chimney leaks in Wallasey, Liscard and Seacombe never get sorted out.

Your Chimney Is Probably Half Somebody Else's

On a terrace or a semi built with a stack on the party wall, that stack is one masonry structure containing flues from both houses. It was built as a single unit, it is pointed as a single unit, and it weathers as a single unit.

Water entering it does not stop at an invisible line down the middle. It soaks into the brickwork, moves through it, and comes out wherever it finds a route - which may be your side of the breast even though the defect is on your neighbour's face of the stack.

The classic version: the weather face of a shared stack has eroded pointing on the exposed side. That side happens to be above next door. Rain drives into it, the stack saturates, and the damp appears on your chimney breast because your side is the colder one or your flue is the one carrying the salts.

You can have every piece of your own leadwork renewed and the problem will continue.

How to Recognise It

The damp is on a breast against the party wall rather than on an external wall.

It has survived a flashing renewal, and often more than one.

It tracks the weather from a direction that does not obviously face your side of the building.

The neighbour has, or has had, the same problem - which is worth asking about, because on a terrace it is common for two households to have been separately paying roofers for years without ever comparing notes.

And on the roof, the giveaway is asymmetry: pointing and brickwork visibly worse on one face of the stack, with sound lead all round.

What Can Actually Be Done

The work itself is straightforward - repointing the stack, renewing flaunching, dealing with spalled brick, sometimes rebuilding above the roof line. What is not straightforward is who instructs it and who pays.

A shared stack is usually a party structure, which in England and Wales means work to it can fall under the Party Wall etc. Act 1996 and both owners have an interest in it. We are roofers rather than surveyors and we will not advise you on your legal position - but we will tell you plainly, in writing, what we found and on which face of the stack.

That written finding is the useful thing. A neighbour conversation that starts with "a roofer has looked at the stack and says the pointing on your side has gone" goes considerably better than one that starts with "I think it might be your fault".

In practice the sensible outcome is nearly always the two households sharing one job. The stack is one structure, the scaffold reaches both halves, and doing one side properly while the other stays as it is means being back in five years.

The Other Wallasey Complication

A good number of these stacks are also disused, sealed at the bottom when a fireplace was taken out and capped at the top. That produces condensation inside the flue, which looks exactly like a leak and is not one.

The tell is timing: a leak tracks rain, condensation tracks cold and humidity. If the damp appears in a dry frosty spell it is not water coming in.

The fix there is ventilation at both ends - a vented cowl at the top instead of a sealed cap, and a vent in the blocked opening at the bottom. It costs very little, and it is worth ruling in or out before anyone puts a scaffold up.