Damp Chimney - advice needed

[RodW1]

Hi there,

The top room in our house had a damp wall, plus part of the gradient from the roof. I took out all the damp plasterboard to identify the problem.

Please see attached image.

The plasterboard was attached right onto these bricks which are part of an unused chimney. The bricks are damp (33% on my damp meter) mostly in the middle of this image but covering the entire vertical. Bricks are dry (12%) at top right and top left.

About 6 months ago a roofer said he couldn't find any roof issue, but said it could be a leak in the chimney. He applied fibreglass paint to ensure it was fully sealed.

I'm wondering if the problem is solved and the damp just couldn't escape through the plaster, or if there is another issue.

Any advice or guidance on next steps and how to assess or treat this would be appreciated!

 

[KenGMac]

RodW1, good evening.

Is the chimney flue blocked of where the fire place was? and is there a vent leading into the old disused flue, also, is the chimney pot capped with a vented cap??

If you can suggest you try your moisture meter on the timber laths, looks like there has been a historic on going leak that has affected the lath??

How old is the property?

Ken.

 

[catlad]

Looks like its sweating.

 

[RodW1]

Thanks so much Ken.

The wooden horizontals are dry (believe it or not). They look like they need removing and replacing but currently they are not damp.

This chimney is not used and none of the fireplaces are visible. I do not know if it is blocked, or where.

Venting - I cannot see any venting from ground level. I have a roofer coming round next week who can tell me if there is any visible venting on the roof, and if it is capped (also not sure). But definitely no internal venting.

The property it approximately 130 years old.

We have no other damp problems in the house.

Thank you so much for your help!

 

[RodW1]

My wife just raised a good point. The other side of this chimney is a 8 year old extension. I'm wondering if some chimney venting was blocked off by this building work.

 

[KenGMac]

RodW1, good evening, again.

Looks as if the [Laths] the horizontal strips of timber are OK.

As for the venting of the chimney flue?
Any disused chimney, the Flue if totally blocked off in the room where the fireplace was in use then Condensation WILL occur on the inner surfaces of the disused flue.
To prevent the Condensation from forming, it is advised that an air vent be installed on the wall area blocking the old fireplace, this allows a free flow of air within the vertical chimney flue.
It is advisable to also fit a "vented" chimney cap, this is installed to prevent rain water entering the top of the chimney flue, and reducing the volume of free water that could cause Condensation in the flue,

In the image posted, there appears to be glass wool stuffed into the gaps around the old chimney flue, both left and right hand side, suggest you remove this material and allow the bricks to dry out.

Get your Roofer to install a vented chimney cal when he visite, and He should be able to point out where the fireplace is situated, stone / concrete hearths are a pointer?

Ken.

 

[tel765]

Flues need through venting.
"Unused" ie, dormant or abandoned flues are vented at either the open fireplace at the base of the chimney breast, or if the fireplace opening has been blocked off there should be a vent in the blocking off material.
Terminals on chimney stacks typically provide the top through venting for the "unused" flue.
Dont pierce the c/breast anywhere else - it could be dangerous.

Your c/breast might contain two separate flues - flues are always separate, servicing one fireplace only. Maybe your flues come from the GF & the 1F.
Sweeping all your flues would be helpful to remove possibilities of flue soot chemicals coming thro the brickwork and attracting moisture.
Pics showing the stack, flashing, pointing, flaunching and pots/terminals will also be helpful.

From what I can see: The plaster lath is pinned below the rafters, and covered at each rafter with a thin timber ripping. The plasterboard was fixed to the timber rippings - you are not looking at the rafters they are above the laths.

 

[RodW1]

Thank you for such helpful replies! As a next step I will ask the roofer to take pictures and ensure the cap is vented. Ill remove the insulation as suggested to let it dry out.

As far as I can tell, it is a single flue to a fireplace on the ground floor (blocked, no vent). If a fireplace existed on the first floor then it has long since been blocked and entirely covered as there is no trace of it whatsoever.

I will update once the roofer has visited next week.

 

[tel765]

I'm presuming that all your chimney breasts are full length ie nothing has been removed?
Counting the pots or terminals on the stack will show you how many flues are in any given stack.

You have to eliminate possible causes one by one - so, if the GF chimney breast goes continuously from the GF up to the stack then best practice would be to open it up at the GF and then sweep it.
And when re-blocking it up insert a vent.

The Back Gutter is located at the back of the chimney breast/stack, & we are looking at the back of the chimney breast - the BG is the most common spot for stack leaks.

Could you post close up pics of the discoloured plaster laths?