Damp in chimney breast

PMMLondon

My house was built in around 1910. It’s an end terrace. The chimneys are not in use and have no fire places. Last week, I noticed a strange stain appear at the bottom of one of the downstairs chimney breasts and along the adjacent external walls. It was not on the other chimney breast but was on the walls adjacent. The areas were sticky to touch. The next day the walls were back to normal. The only sign was a sticky, yellow substance on one of the skirting boards.

I called in a local damp company who within about 30 seconds, using a damp meter, said it was rising damp and that I’d need a new damp proof course. Quoted £1,6000. He looked outside, said the render was fine. There are air bricks outside where the chimney breast is, but no vents inside. He said he’d add air vents inside for good air flow.

It had been raining when I noticed the problem. I asked if it could be a leak from the chimney on that side. He said no as the wall outside would show a line of damp coming down. The previous owner told me they’d had a leak from that chimney which was repaired, which made me query it. The chimney has render all around it. I was thinking about asking a roofer for their opinion. 

There is no guttering near the chimney breast and it’s not leaking anyway. Just before noticed the damp, I put some wet washing on the radiator in that room and turned the heating on. I also wondered if it could be to do with condensation. 

I’ve read that some say rising damp is a myth and although I could get a couple more views from damp companies, I think I might feel more assured with an independent damp surveyor. 

Please can you tell me if you’ve used one and if you can recommend one in Essex. 

Many thanks.

FreeBear

PMMLondon said: I’ve read that some say rising damp is a myth and although I could get a couple more views from damp companies, I think I might feel more assured with an independent damp surveyor.

If you can find an independent surveyor who is not affiliated to the Property Care Association (PCA) and has no links with a damp treatment company, you stand a better chance of getting an honest appraisal. But it won't be free - If he comes in sticking an electronic damp meter in the wall and declares "rising damp", you'll know you've been had again.

Electronic damp meters will only give a proper reading when used on untreated timber. In any other material (brick, plaster, cement), there will be all kinds of salts & chemicals that will render the readings meaningless. The only way to get a true measure of damp in the wall is to drill a hole and place a sample of the dust in a Carbide Meter. Few surveyors will have one or know how to use one properly...

Whilst an electronic meter can be used to highlight an area that might be suffering from damp, it needs to be used by someone with experience, not a salesman.

For chimneys, I'd suggest calling on a roofer or chimney specialist - Things to look for are -

• Deteriorating pointing.
• Failing/cracked flaunching (the cement around the pots at the top of the chimney).
• Faulty/leaking flashing.
• And for any unused flues, the absence of any chimney pot caps.

The last one will be easy to spot, and if the pot is uncapped, rain coming in that way is the most likely source of any damp.

Doozergirl

You should have a vent at the bottom and your chimney should be capped, but only with a cowl or pepperpot that keeps rain out but air in.  It's important that you still
enable a flow of air through the chimney. 

Please don't call any more damp 'specialists' out.   The first thing one should be doing with a chimney is looking at the top of it, not the bottom.  If a leak wasn't on the external wall of the chimney you'd never see any evidence on the wall outside,
it would just leak straight into the house.  It's preposterous to suggest rising damp without even looking at roof level.     Might be worth looking in the loft at the chimney though, and the timbers around it.  

Feel free to post pictures of the outside wall of the chimney at ground level.  If damp were getting in from outside, there would be evidence of the ground level breaching where the DPC should be.  Damp doesn't just rise for no reason.    

PMMLondon

Thanks, both.
Here’s a photo of the wall.
I have arranged for a roofer to take a look tomorrow. The chimney doesn’t have pots on, it’s flat across. I’m not sure what exactly is up there enabling air flow so will see what’s he says. At the very least it sounds like I need a vent added to the chimney breast.

FreeBear

PMMLondon said: At the very least it sounds like I need a vent added to the chimney breast.

If that air brick goes through the wall into the unused flue, then it is unlikely that you'll need an additional vent on the inside. If anything, having an internal vent as well could well be a source of a cold draught.

davilown

That part of the wall seems wet compared to the rest. Is the guttering blocked and/or is that the direction of the prevailing rain?

PMMLondon

FreeBear said:

PMMLondon said: At the very least it sounds like I need a vent added to the chimney breast.

If that air brick goes through the wall into the unused flue, then it is unlikely that you'll need an additional vent on the inside. If anything, having an internal vent as well could well be a source of a cold draught.

Thanks for clarifying. The roofer can’t now come until tomorrow. Hopefully, I’ll get some answers then.

PMMLondon

davilown said:

That part of the wall seems wet compared to the rest. Is the guttering blocked and/or is that the direction of the prevailing rain?

You’re right. I don’t know why that is, the guttering doesn’t appear to be blocked.

stuart45

The downside of an exterior vent is that cold air is being drawn into the flue which can create cold spots on the inside. They used to vent cavity walls with air bricks until this was realised.