Damp from chimney. Evidence in loft and on external wall

[stewneedshelp]

IMG_1524

• stewneedshelp
• 6 Nov 2015

The pine end wall after rain

IMG_1446

• stewneedshelp
• 6 Nov 2015

Plasterboard removed. Bricks and timber stay dry

IMG_1432

• stewneedshelp
• 6 Nov 2015

Damp on plasterboard and under arch (also wet on the wall under arch)

I have a problem in my bedroom loft at the chimney area.
The chimney has 4 chimneys pots all with ventilated cowls.
The wet in seen mainly under the archway created by the joining of the separate flues.

The interior wall was plasterboarded and dampness soaked some of the plasterboard when it rained. (See photo)

Thinking there was a leak dripping inside I removed the plasterboard but no leak drips internally on the brick wall even in adverse weather conditions. (photo)

Externally 3 chimney elevations have been repointed, the flashing inspected on all elevations and new concrete was put on the top of the chimney when the 4 cowls were positioned. Also the external wall on the pine end has been inspected and appears sound as there is no evidence of 'blown' render.

Today it has rained hard and the pine end has shown a particular wet pattern (photo). After it has rained, this pattern is more or less in the same position.This marking is there to a lesser extent even when it is not raining.

Has anyone any idea what might be causing this water damage?

Thanks
Stewart

 

[KenGMac]

Stewart, hi.

I copied and pasted the first image you have uploaded, zoomed in and there are indications of Ferns or something growing out of the exposed, as yet not Re-Pointed area of the exposed Chimney head, this is a possible candidate for rain water ingress?

Ken.

 

[stewneedshelp]

Thanks for your reply Ken.
Yes it is a small (very small) growth of some kind.
It's so tiny compared to the amount of wetness though. Surely that it must be more of a weakness to let in so much water.

 

[stewneedshelp]

Although this side hasn't been pointed - the existing pointing had been examined and is said to be in reasonables order with no loose parts.

Perhaps that growth has appeared because the chimney is wet most of the time ( ...and not the cause of the wetness...maybe!?)

 

[ree]

1. The flaunching on top of the stack needs inspecting and perhaps videoing - same with the lead flashings.

2. Plus, as above, the gable face of the stack needs re-pointing. Judging from your pic the re-pointing to the cheek of the stack is a pretty poor job - more smeared than neatly pointed.
Rake out to 22mm min.

3. All your flues should have been swept - judging by the gable pic the central, sooty staining corresponds to the internal damp stains where the flues gather. Presumably, if the flues are redundant then they are ventilation terminals in the pots?

4. There are water stains below the verge undercloak - the pointed verges should be examined and videoed by the roofer. Maybe water is creeping around the undercloak?

5. The gable render shows water penetration at the corner. The "Tyrolean" (?) render cover is none too clever.

FWIW: read up some of my back posts on flues and chimney breasts - esp. hygroscopic reactions.

 

[stewneedshelp]

Thank you Ree ...plenty to think about in your answer...thank you very much.

I now tend to think the problem is indeed with the flaunching at the top.

It was "improved" some months ago but merely by adding fresh cement on top and curving the surface more

I now guess that this area is porous and dripping wetness into the chimney itself in some way. This would account for the particular wet markings in the loft and those on the external wall.

I presume that the flaunching should have some form of dpc which must have broken down somehow....can that happen?

I suppose that the existing flaunching now needs to be removed and remade.

I think that's the next thing to try....I hope it's not too big a task for a professional...should I employ a roofer or a builder?

 

[ree]

A roofer could replace the flaunching - toppings rarely work - but have the roofer provide a before and after video.
The pots and any other terminals must be carefully bedded, and not just pushed into the mix.

Some of the other items listed above could be done by the same roofer depending on the stack work.

Some chimney stacks were built with a lead sheet DPC - but its more of a mini membrane. Unless the stack is re-built its impossible to retro-install one.

None of the above is a "big task".

If you would, why not post any quotes, and their prices on here then other DIY'ers with an interest in your post could get a few ideas about costs etc.?

 

[stewneedshelp]

I've just noticed this slipped tile/s at the base of the chimney (photo taken from the rear of the house)- could this be the root of the damp coming into the chimney area?

 

[ree]

No, thats not the weak link. There are no "slipped tiles" just an awkward setting out.

Clumsy attempts to caulk or point in the flashing can be seen - the flashings must be removed, the area cleaned up and the flashings replaced correctly.

Presumably your roof planes were covered with underfelt when they were re-roofed? If so, any entering moisture would run down the roof under the tiles to eventually safely enter into the gutters. Anyway, thats the theory.

As i indicated above your leak(s) is actually on, or tight to, the stack.

 

[^woody^]

The location of the damp indicates moisture soaking through from the flue, rather than down from the roof or flashing.

But if that is a damp patch along the top of the exposed chimney, then its probably a flashing issue.

If its damp from the flue, then its either the flue caps or lack of flue venting.

 

[stewneedshelp]

Thanks for all these helpful suggestions and ideas everyone.

To fully clarify- there is no evidence of any wet on the brick wall.The dark area on the top is old staining but this hasn't changed even in severe wet and windy conditions lately.

The felt under the tiles in this area appears to be in good order and there is no evidence of seeping water anywhere on it.

The dark areas on brickwork and on timbers to the left is due to the former occupation of bats....now definitely all gone some time ago.

The wet that is seen from the inside room is on that section of vertical wall beneath the arch.
This pattern of wetness definitely changes depending on degree of rain falling ...this seems to be the outer wall of the building.
I now think that this wetness was in the past, moving along plastered surfaces to then show itself on the front of the former plasterboard (in photos).

The wetness on the outside wall corresponds to the area of wetness under the inside arch on the wall.

So the wet is entering and dropping down and then marking that area where the chimneys split.

The rain must be entering from either the top of the stack (the cowls have ventilated covers) or from flashing area...I agree!

Ventilation:
The dampness remaining in the chimney I agree doesn't help.
Originally 2 bedrooms had open fires (now blocked and only with 2 sliding plastic ventilator bars at skirting level)
One fire was in the backroom downstairs (now with minimal ventilation) and without any fire at all.
The Front room has a cast iron insert with a gas unit with open flame going into open chimney area. This fire is only used now and then during the winter.
So the 4 flues don't really get the heat (or ventillation I suppose) as is needed to dry them adequately.

Thanks again..... now to decide what I need to do first!