Damp in parapet wall - issue with coping stones or render?

14 Jan 2013
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United Kingdom
Hi all,

This is my first post although I've been a lurking member for some time and have found this forum incredibly useful so far!

I bought my first home in July 2012 - it's a 1904 terraced house in Bristol.

When I moved in there was water staining and damp on both chimney stacks - as seen in this image of the rear chimney stack.
I had some remedial work done to re-seat the leadwork around both chimney stacks and this seems to have largely resolved this issue. One of the roofing companies, however, mentioned that there were signs of damp on the parapet walls and proposed to hack off all the render, re-do the leadwork, apply new render and replace all the coping stones. I decided not to proceed at the time.

12 months on, the damp in the parapet wall seems to be working its way down and is emerging in the front bedroom. There is a damp patch high up the party wall, right in the corner (probably underneath the horizontal coping stone).

I'd appreciate any views on:
- Whether coping stones themselves need to be replaced;
- Whether damp could be penetrating cracks in the render on the parapet wall, and working its way down;
- Whether chimney stack and parapet wall render looks damp, or just a rich mix and whether this is an issue.

Front of house

Rear of house

Many thanks!
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There is some vegetation growing where the parapet from the apex reaches the left hand chimney stack in picture 1. The pointing and brickwork on the hindmost part of the left front stack is very badly eroded. I would say that it needs a thorough overhaul, together with any of the adjacent coping stones and flashings.

It's been pointed out that the following is wrong - I misread the post and the images - apologies to all! Any comments made refer to the neighbour's chimneys.

BUT... the chimneystack on your side of the roof has been removed back to the party wall just below the tiles, it seems. It is often a problem when half a chimney is removed, and the other side belonging to the neighbour remains.

The old brickwork can harbour combustion products from years of use, such as nitrates and sulphates, which have permeated the brickwork, and create an easy route for moisture to enter the party wall, causing the sort of problem you have. The neighbour may have no problem, due to through ventilation of the flue from the rooms below. On the other hand they may have a problem they are not aware of.

You may need to prevent water ingress via your neighbour's stack, but your neighbour may not want to pay for this, or even allow you to do the necessary work at your own expense.

A good roofer will give you recommendations and a price, but you will need to involve your neighbour for the any of the party wall works to go ahead which involve their property.

Of course, notifying your neighbour may involve them in unexpected expense which may cause resentment, and even lead to a dispute, so tread carefully.

The left neighbour's front stack is obviously water damaged, and showing signs of efflorescence.
The same neighbour's rear stack chimney pot is dangerously leaning - according to the pic.
Your rear loft pic shows amateur rafter repairs, and active leaks in the roofing and at the chimney breast.

Do you have, or have you had, chimney breasts on the left party wall?

Flashing is lacking on your stacks where the render meets the coping stones. Plus the render should have been bell cast and stopped short of touching the coping stones.
Presumably the render was a remedial application rather than a possible stack(s) re-build.

Its hard to comment on the copings and parapet render - the pics need detail. Flat coping's are always suspect. Are the flags throated?

Your front fascia appears to be "rotting". The rear gutter union is dipping and will hold water/debris.

The front elevation render has stonework(?) grid pattern beds grinning through.
Looking at the interior picture the water ingress is more than likely due to the back of the chimney where the vegetations growing.
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The loft interior pic is of "the rear chimney stack" (sic).
In other words, the left hand stack in pic 3.
Awrite yanky! The vegetations not good though is it. And efflorecense is nout to do with water damage.
The immediate water ingress issue is in the front bedroom on the right hand party wall, some distance from the chimney stacks - hence the suggested diagnosis of an issue with the coping stones or render on the parapet wall.

Ree - no the flags are not throated. To be honest, they look more like patio slabs to my untrained eye! Any thoughts?

I cant say much more than i posted above. You will have to either go up yourself or get others to diagnose a priced solution for you. Whoever you use should examine both party walls in the loft, as well as the roof.

At the moment, you'll probably find that most good tradespeople have lots of work on.

Maybe come back on here with details of any quotes?

If, on diynot, you've followed recent posts about similar parapet & roof difficulties, then water testing might take you forward somewhat.

Running an angle grinder down the flags will cut slots.

No half chimney stacks have been removed. Where is your evidence for saying thats the case?

"Awrite yanky!" ... is that your idea of cool street talk, or simple illiteracy?

"The vegetations not good though is it." ... I dont know. I'm not smoking it.

"efflorecensce ... nout" ... Remember the old saying: "If in doubt say nowt" especially when you cant use a spell checker.

Unfortunately, water has everything to do with efflorescence. Excess water in a building material is water damage. When the water meets salts it dilutes them & transports them to the surface.

The flashing at the chimney stack back is called the backgutter.


I notice that you thank colind86 for a"useful post". Given that he doesn't know what he's talking about, and didn't seem able to locate himself in terms of the pics, then your idea of a "useful post" seems a bit strange?

So, three confused DIY'ers following one original question, perhaps a first? Whatever, guys, i implore you, do not give up the day jobs.
Well ree, its just aswell im not paid to spell isnt it. By the look of it the vegetation is growing out a non exististent piece of lead where the coping stones meets the back of the chimney. Which isnt technically a back gutter now is it? And effloresence is water and salts read up on google it isnt as you say guaranteed water damage! As for smoking the vegetation I suggest you start! Maybe chill you out a bit! :rolleyes:
The flashing at the chimney stack back is called the backgutter.

Aka saddles where we come from.

Your posts are convoluted and confusing to a diyer... typical pencil pushers blurb.

Colins post is concise and straight to the point.

Calling construction professionals diyers isnt going to earn you any respect on this forum! especially as you have just joined and you dont know the posters.

You dont know if the back gutter lead is present or absent, neither can you see if the coping stones stop short of the stack or butt up to it. If they would fix a front lead apron why would they leave out the back gutter?

Given that vegetation on the back gutter would be a possible source for water entry - a possibility.
The facts are that we can clearly see water stains and efflorescence higher up on the stack, these must be derived from water damage in the stack - a certainty.

"isnt technically a back gutter" - read my first para. You are clutching at straws here.

"effloresence (sic) is water and salts" - who said that it was anything else? I dont need google, i've already provided you with a little explanation of what happens (see above).


Ive read back to some of your excellent and useful past posts. I learned things i didn't know.
Neither do i know why you choose to disrespect me?
Anyhow, its water under the bridge, life is short, i've got to move on.

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