Damp chimney in attic

[DIYdampbusting]

We're in a Victorian terrace house with a damp problem in the attic. The ceiling and top of the walls near the chimneys dry out in good weather and then get wet again when it rains. We've had the chimney stacks repointed and flashed etc, and since had other roofers look at the work, and all have said it looks a sound job. There are no broken tiles etc. all flues have been swept, one has a solid fuel liner and the rest have gas cowls on top and vents in the bottom.

Any ideas what's causing this and a possible solution? View media item 63855

 

[Nige F]

Look @ the flaunching that`s on the top with the pots/gas terminals through it . If there`s some cracks - douse it with Thompsons water seal ( or similar ) It worked for me

 

[DIYdampbusting]

Last time I looked the flaunching looked pretty good, and none of the other roofers thought there was a problem with it. The damp on the ceiling shows 5 sort of semi circles of damp some being bigger than others, there are 4 gas cowls so I wondered if the rain was getting down the gas terminals- they're the silver aluminium type with fins cut out the sides. Does this sound likely?

 

[dann09]

Is there an access trap in the ceiling to the loft space above?

Roof leaks, if thats what it is, can occur in one place, and present below in another. But that close to a stack would point the finger at the stack area.
Is there a back gutter directly above the stains?

Thing is, you dont want people clambering about your roof esp. without roof ladders.

Gas cowls have horizontal slots and are fixed with clamping plates, when were yours installed?

 

[DIYdampbusting]

The gas cowls are installed into a metal plate that's been cemented over. I'm not sure what a back gutter is, but there's lead flashing and soakers all round the chimney. The only place there isn't lead is between the chimney and the ridge tiles. Other houses on the row are also like this.

I can get into the attic space above the room, it seems dry except for the chimney. All the roofing felt is in good condition.

 

[dann09]

1. Perhaps go and enquire with neighbours - have they had similar difficulties, if so what did they do?

2. You have nothing to lose trying Nige F's proposition.

3. From what you say, you wont have a back gutter.
Is any rendering present on the stack?
Do you definitely have soakers below the step or cover flashing?
A long shot might be installing a saddle flashing where the ridge meets the stack. But only as a v. last measure.

4. In the "attic space" does the brickwork appear damp - is it wet - is there a pattern?

5. Does damp appear on all four flue positions as in the attic below?

6. Whats the history of this: when did the stains first appear - after any particular work?

7. Why not zoom some stack pics and post them on here?

 

[Nige F]

Last time I looked the flaunching looked pretty good, and none of the other roofers thought there was a problem with it. The damp on the ceiling shows 5 sort of semi circles of damp some being bigger than others, there are 4 gas cowls so I wondered if the rain was getting down the gas terminals- they're the silver aluminium type with fins cut out the sides. Does this sound likely?

could be - as they are just sitting on an ali plate that`s been pugged over , gotta be a weak point

 

[DIYdampbusting]

Here are some pics of the chimneys stacks. I can't get to the top to photograph the flaunching etc.

To answer some of the questions. Damp appears on all of the flues on chimneys on both sides of the room. The ceilings were damp when we moved in, and have since had both chimneys repointed/rendered and the lead work redone and gas cowls fitted. One stack is sandstone, the other is rendered breeze block. If anything the problem's now worse. The brick work in the attic space shows as damp using a damp meter. All flues were blocked with birds nests and soot when we moved in, but have since been swept.

Could it be that the plaster/brick work is hydroscopic from previous damp coming through sooty flues?


View media item 64156 View media item 64157 View media item 64158 View media item 64159

 

[dann09]

1. What do the neighbours on the other side of the stone stack and the rendered stack have to report? Dry, damp?
How does the ridge meet the stack elevation on their sides?

2. The lead saddle flashings on both stacks could be suspect, esp. on the rendered stack side where there seems to be an excess of sand and cement.

3. The above is guesswork, given that the stacks appear to be in good order.

4. As you suggest, there could be chemically contaminated plaster on the c/breasts.
Perhaps soot remains in the flues, but, short of a camera view, its impossible to know.
Were the c/breasts in the loft wet, or showing a stained pattern?

5. FWIW: the left hand stack was probably rendered as as a remedial precaution against precisely this problem.

 

[DIYdampbusting]

The chimneys in the attic are wet (damp meter above 50%). Can you chip back contaminated plaster to the brick and paint on an anti-salt chemical?

 

[dann09]

You can take off contaminated plaster to brick, but dont apply any paint-on remedies. Merely render with S&C&L and an additive.
Massive amount of material about this subject on this forum.

Wet means, as in, can you see or feel wet brickwork? Is there water on the brick surface?