A chimney is a free-standing masonry wall, exposed on four faces, standing at the highest point of the building and interrupting the flow of water down the roof. Almost everything follows from that.
Every other part of a pitched roof is designed to shed water downhill. A chimney is a vertical masonry structure standing in the middle of that, and it changes the behaviour of everything around it.
It is exposed on four faces rather than one. A house wall gets weather on the outside and is warm and dry on the inside; a stack above roof level is outdoors on all sides, top and bottom, with no shelter from anything. The mortar joints on a stack therefore weather several times faster than the joints on the wall of the same house, in the same mortar, laid by the same bricklayer.
It is the tallest thing on the building, so it takes the highest wind loads and the most driving rain.
And it is a thermal chimney by design - even a disused one - which means it moves air and moisture through itself in ways a wall does not.
The second structural reason is geometry. A chimney sitting in a roof slope splits the flow of water coming down that slope, and all of that water has to be collected and taken round it.
That is what the back gutter above the stack is for, and it is doing more work than any comparable area of the roof. On a wide chimney on a shallow pitch, everything from the ridge down to the stack is being funnelled through one lead channel and out along two sides.
Then it has to be handed back to the roof below via the side flashings and the front apron, past a junction between masonry and covering that has to be weathered at every single course.
That is a great many interfaces in a small area, and interfaces are where roofs leak.
Worth stating plainly, because "the chimney leaks" is not a diagnosis.
The flaunching - the mortar bed on top holding the pot, which cracks with age and then collects water instead of shedding it.
The pointing - eroded joints letting driving rain straight in.
The brickwork - spalled faces where frost has blown the hard outer skin off, leaving an absorbent surface.
The leadwork - four separate pieces, failing in four different ways.
The flue - unlined and open, bringing water down from the top.
Which of the five is the entire question, and it is why new lead so often changes nothing.
There is a sixth possibility here, and it has a recognisable signature.
Salt extraction beneath Northwich has left the town with a documented history of ground movement. Most of it is long settled, but buildings that moved once carry it in their fabric.
A chimney is the most sensitive part of a building to that, because it is tall, narrow and rigid. When the building beneath it moves, a stack does one of three things: it leans, it cracks in a line, or it pulls its flashing out of the chase on one side only.
The signature is asymmetry and straight lines. Ordinary weathering is even, because the whole stack gets the same weather. Cracks that run in a line through several courses, a flashing that has come out on one side while the other is untouched, or a stack that is visibly out of plumb are not weathering.
It matters because the repair is different. Rigid mortar packed into a joint that is going to open again has a known expiry date; a stack that is genuinely leaning is a structural question rather than a roofing one, and the right person to look at it is a structural engineer or a surveyor. We will say so rather than keep selling you flashings.
A visibly leaning stack above a path or a pavement is also a safety matter and should be treated as one.
Keeping the back gutter clear, which is free and almost never done.
Repointing the stack when the joints start to open rather than when the damp appears, because masonry that has never been allowed to saturate does not spall.
Renewing flaunching when it cracks - one of the cheapest jobs on a roof and one of the most consequential.
And capping a disused flue with a vented cowl, which removes an entire category of problem at once.
The rest of the series, on the questions people ask most.
Every town has its own page, written around what the roofs there are actually like. Start with the main roof repairs page.
“Excellent workmanship by Buddy Evans. I was impressed and amazed at how quickly the job was done. Obviously due to many years' experience. I've used several mediocre or bad roofers in the past and now I've finally found a good one.”
Czeslaw birukowsk“Excellent work from the lads at roofline solutions. I had a leak in my valley, they came out and sorted it within a day.”
Chris Hollewell“Would highly recommend roofline solutions they arrived in time an explained to me what need to be done well spoken and polite”
Kyle CummingsDescribe what is happening and roughly where you are, and we will come back to you — usually the same day. If water is coming in now, please call instead.
Prefer to talk? Call 07464 259566 · WhatsApp 0044 7464 259566 · Email Evensbuddy@yahoo.com
We cover Chester, Cheshire, the Wirral and Flintshire from Elton, just north of Chester.
2 Manley View
Elton
Chester
CH2 4QF
Almost all of our work happens at your property rather than here, so please call before travelling.
Monday – Friday — 24hrs — Emergency Call-Outs
Saturday — 8:00 – 19:00
Sunday — 8:00 – 19:00
Weekday emergency call-outs are answered around the clock. Weekend cover is 8:00 to 19:00.