venting chimney

[JBean]

Hi

We're in an Edwardian house and the 2nd floor (attic) chimney breast has had patches of damp since we moved in a year ago. We've had the flashings replaced and work done on the roof. We've now stripped off the plasterboard over the chimney breast to reveal the brick underneath (the outer walls are sandstone).

The opening is still there - see photo [edit - apologies for it being sideways: I've no idea why!] - and, after we'd removed several large bags of black mortar lining that had fallen off over the years, our chimney sweep advised that the chimney was pretty clean. Although we won't use it again as a fire, we plan to put in a cast iron fireplace (not original, but Edwardian).

Now, my question. The sweep has told us that there is no vent in the chimney. There is certainly no pot, and he says it has all been sealed up, and recommended we install two air bricks - one in the chimney and one in the back of the opening. Does that sound sensible? Our builder has said he would need scaffolding or a cherry-picker to insert an air brick in the chimney, which of course makes it rather expensive! If we put in a fireplace it will not be airtight, so does that mean we don't need the air brick in the opening?

We're keen to get this right and get rid of the damp, but obviously don't want to spend money unnecessarily. Advice very welcome.

 

[88v8]

So has the flue been sealed up at the bottom? If not, as you say with a fireplace it will be open so I'm confused why he would recommend an airbrick in the bottom.

Airflow through the stack is very worthwhile. A little continuous airflow will dry a lot of damp.

Yes, an airbrick in the stack. The openings in the airbrick must be quite small - not more than quarter inch. Otherwise you risk bees setting up shop.

DIY ??? ..... ladder.... tie it at the top, hire a cat ladder and climb up.
Lime mortar, chisel, not difficult.
Or, easier, just drill four inch holes through into the stack and keep the bees out with stainless mesh fixed with brass screws & stainless washers.
https://www.amazon.co.uk/Stainless-Steel-Woven-sizes-Aperture/dp/B00AWQEDG4?th=1
Working on the roof is not difficult when one becomes acclimatised, and you will then not be at the mercy of builders.

Ivor

PS to avoid rotated pics, rotate them in your photo editing software and save them.

 

[JBean]

Ivor, many thanks. The chimney is open at the bottom so I agree it doesn't seem like we will need an air brick, as we will be keeping the opening and installing a fireplace.

Good advice on the bees! We will look at an air brick or mesh. Not sure hubby or I are up to ladders on the roof, but we have a friendly builder who might be persuaded to nip out the attic window, drill some quick holes and attach some mesh. Forgive the daft question - do you mean four holes, each an inch across, or one hole of four inches?

 

[88v8]

Four holes of one inch. If not too far apart, they can be covered by a not very large square of mesh.

I spent over £1,000 and a good deal of work evicting bees from our stack, and it didn't end well for the bees.

Ivor

 

[DavidB]

We're keen to get this right and get rid of the damp, but obviously don't want to spend money unnecessarily. Advice very welcome.

Hi
I would be keen to get this right too. The best solution in my opinion would be to uncap the chimney opening. Install a new chimney pot matching period / existing. Then install a breather cap to the new chimney pot. Keep the fireplace open and it will allow air to circulate and dry out the bricks. Then if in the future someone wanted to reinstate the chimney they could easily do so. If you still have damp then you needed to draw out the salts from the chimney. There are solutions for this, but even repointing in lime can be sufficient to improve excess salts drawing moisture out of the air.

If you drill holes in the wall or install air bricks that will make reinstating the chimney more tricky. I would do the more easily reversible option. I appreciate that might seem more expensive, but it might not be if you look at the future costs.

However, this is just my personal preference. So please don't think I am being critical of your suggestion.

 

[88v8]

I don't disagree. Had this been a ground floor room where the fire is likely to be reinstated then you are absolutely right.
The hole drilling approach is applicable to lined flues (woodburner or boiler) where the stack itself should be vented, but also flues already sealed where there is no practical likelihood of reinstatement. In the latter case it also has the merit of minimising heat loss.

Ivor

 

[JBean]

Thanks for the further advice. We are still thinking what to do for the best. Our roofers (who should have spotted this problem when they had scaffolding in place) have just quoted for installing an air brick in the stack AND a 'ventilated mushroom cowl' - not sure why they think we need both (especially when at first they thought we needed neither). It's a lovely £580 + VAT quote for installation via a cherry picker...

 

[88v8]

Caramba. Can you not climb up... For that money you could buy your own roof ladder several times over.

Ivor

 

[JBean]

Sadly, the roof is effectively four floors up - three floors of house plus a drop caused by the slope of the road. So neither of us will climb out at that height.