damp area on my chimney.

[richard306]

i have a damp area that comes and goes depending on the rain. Its on the upper part of a chimney in my spare bedroom which is in the eves of the house. I have had roofers out to check the flashings and they are sound and only 5 years old.

The chimney services a gas fire and two of the three pots are capped.

One roofer mentioned spraying the chimney with a sealent to stop moisture coming in through the brickwork.

There doesnt seem to be any cracked/broken tiles either

help!! any ideas?

 

[redtonybbb]

Ex roofer(advanced C&G) Chartered Surveyor.The chances of damp coming through the chimney are small so I would not recommend spraying anything with a sealant,which may actually cause damp given heat from the gas fire needs to get away.Most leaks to chimneys where the flashings are ok are when you get a combination of wind and rain together which may drive up beneath the cover flashing.The cover flashing needs to be wide enough or long enough to prevent rain driving beneath when the weather is bad.Things to check are cracks in the lead gutterback/the weight of the cover flashing ie code 4./The pointing of the flashings.The correct soakers or cover flashing for slates or tiles.The leadwork needs to be dressed properly to the roof.Is the leadwork fixed sufficiently into the structure.Anything to do with water penetration needs to be inspected closley...and don't forget most water gets into the property from a higher point generally to where it actually shows as it runs.Good luck.

 

[DonJenzus]

Hiya.

When you look at the damp area, does it look like it gets wet at the area where the gas fire pot is or is it more at the area of the capped pots?

I think that if the moisture comes from the pot in use, then there is a crack in the chimney, or it leakes from the roof´s and the chimney´s joint.
In a healthy chimney the hot air coming from the gas fire should dry the pot. But in a weathered one it´s possible that the rain gets in to the crack which absorbs the moisture too deep and the the hot air is not able to dry it.

If you don´t have anything organic materials at the damp area, then there is no worries in the future. But if there are, then you should check that there is no fungus or mould in the walls. You should also check the ceiling that the insulations (if organic) are ok.

 

[justlead1]

Hi You mentioned that the chimney flues were capped of allowing air flow through unused flue can help. Also chimney DPC fitted as the chimney exits roof stops this. Traditionally the chimney had a area to dry out in loft space but with the additions of living area in the roof any dampness shows.

 

[^woody^]

First the basics. Moisture gets into the stack by three routes - via the roof or flashings, via the brickwork, or via the flue .

As this occurs during rain, then we can probably eliminate the flue route - but check the cappings on the redundant flues or if the used flue needs a different pot or cowl .

If the flashings and tiles have been checked properly (?), then its not here.

So we have the brickwork.

Routes for excess water penetration will be poor pointing, cracked/blown bricks and defective flaunching/cappings.

There should be a DPC in the stack to stop water soaking downwards below the roofline. If this is missing, then the options will be to either rebuild and add a DPC, or as the roofer says, give the exposed brickwork a really good coating of a suitable water repellent - but this is not a long term solution, between 5-10 years depending on exposure

 

[noseall]

....and 4. via hygroscopic salts.

 

[^woody^]

Thats a sub-section of any of the first three