Chimney Cowls

[thebadger7]

Hi folks

Recently had my chimney pots replaced

Went for aluminium covers, as they completely cover it and have an air gap for ventilation. Regretting it a bit, the pepperpot ones look a lot better but I was told they can let water in where they sit in the pot.

Birds also noisy on metal like this fella!

Anyone have any experience with them? Do you seal them in or do they sit under own weight?

Thanks

 

[a twig]

Those pepper pot cowls are also often known as elephants foot cowls - usually they do sit happily under their own weight but traditionally a bit of mortar is used to prevent water ingress between them and the top of the pot.

Nowadays with all the various weather proof adhesives available often a thin smear of that is used instead.

We have used those cowls for disused chimneys and been very happy with them, good ventilation and no rattling noise from the birds

 

[a twig]

There’s a previous thread here which explains nicely with pictures:

S

Thread 'Chimney rebuild'

Jul 28, 2018

Pics of the story of our chimney on our mid terrace Victorian property. We knew the chimney was ropey (you could put your arm directly into each of the 4 flues in the loft where the mortar had been washed away) so as we were going to strip the cement from the front and re-do in lime we got the scaffold extended and the old chimney taken down.

The builder went up there to start taking it down and relayed the story to me the following day. "Took me bolster and hammer. Didn't need either of em"



He took the whole lot down by hand, just picking the bricks off one by...

• steveb
• Replies: 4
• Forum: Period Property Discussion Forum

 

[thebadger7]

Thanks Only thing that puts me off with pepperpot ones are the use of a seal which will inevitably fail eventually. Maybe I'm over thinking it...just want to get it right while scaffold is up as access is tricky if any future issues. Scarred by leaking chimneys!

 

[stuart45]

There isn't a massive amount of rain that get's into even an open chimney pot. Years ago when the flues were parged the amount of water that went down the pot was easily absorbed into the parging and evaporated away. Once liners started being used, especially stainless steel ones, even a cup full of water would make it's way down into the stove. Having an elephant's foot cap on the pot would virtually eliminate any moisture, even if unsealed.
One point about chimney pots. They should have around 25% of them built into the masonry. The majority of builders only use the flaunching to hold them in place, which is why you often see the older ones leaning over really to fall.

 

[thebadger7]

Thanks, we don't have any liners in our flues. Previously we'd get damp in attic room which looked like water ingress (it followed flue location). Now I'm worried theyre going to fall over... definitely not 25% in. They were replaced when flaunching was re done as old pots had had it

 

[stuart45]

Thanks, we don't have any liners in our flues. Previously we'd get damp in attic room which looked like water ingress (it followed flue location). Now I'm worried theyre going to fall over... definitely not 25% in. They were replaced when flaunching was re done as old pots had had it

They won't fall over in the near future, especially as they are not that tall. The majority of builders use the flaunching to secure them. It's just that when building a chimney the idea was that the pots should stay in place as long as the chimney itself, not start to fail after 70 or so years. It's normally the tall ones like the 3ft ones or more that you see leaning over. I've never seen one that was built into the brickwork with this issue.
Technically, the flaunching is there to make the top weathertight.

 

[IHateDamp]

Recently had my chimney pots replaced

Went for aluminium covers, as they completely cover it and have an air gap for ventilation. Regretting it a bit, the pepperpot ones look a lot better but I was told they can let water in where they sit in the pot.

How much of an air gap is under those metal ones ? Can't really see where it is / how it works

 

[a twig]

Thanks Only thing that puts me off with pepperpot ones are the use of a seal which will inevitably fail eventually. Maybe I'm over thinking it...just want to get it right while scaffold is up as access is tricky if any future issues. Scarred by leaking chimneys!

As per other posts - any leakage should that fail is small beer, fit it, forget about it, move onto other issues

 

[thebadger7]

How much of an air gap is under those metal ones ? Can't really see where it is / how it works

About 20mm

 

[Stevers]

They should have around 25% of them built into the masonry.

Many chimneys aren't built big enough for the pots to be built in including ours, but our builder used bricks split lengthways for the top course, and with the corbelling of the lower courses, there was room to bury them a decent amount. Whether those split bricks will prove to be a point of weakness for ours is another question, but looking good so far (hard Staffordshire Blues with 1:1:6 cement/lime mortar).

We fitted elephants' feet over twenty years ago, and yes I also worried about them leaking so ours were siliconed in. There's no sign of the silicon failing in that application, or for that matter any question of ever being able to lift the cowls off again.


Due to a manufacturing fault the lids separated on all six cowls, one came ajar and had to be rescued by the fire service, and a second was blown completely off, clearing the porch below and landing in one of the few places where it could without damage. Those that lifted off, or could be lifted off have been epoxied back on. All six also have stainless steel pins epoxied into holes round the edge to make sure that none of them can ever do anything like that again.

We had a period of very heavy rain (and wind) when the first lid came off. That was for a ground floor flue with vent, and the rain entering the stack did cause damage to decoration in the ground floor room below the stack and in the basement room below that, but not in the room where its fireplace had been or the upstairs room directly below it. In contrast when the second lid came off (and it was off until I'd lined up enough jobs and the right time of year to warrant bringing scaffolding in) there was no evidence of any water entry at all.

 

[stuart45]

Many chimneys aren't built big enough for the pots to be built in including ours, but our builder used bricks split lengthways for the top course, and with the corbelling of the lower courses, there was room to bury them a decent amount. Whether those split bricks will prove to be a point of weakness for ours is another question, but looking good so far (hard Staffordshire Blues with 1:1:6 cement/lime mortar).

Pots in the past before liners came in were normally designed to be slightly too big for a 9 inch flue. The idea is that the base sits on about an inch of brickwork all around. You then build a few oversailing courses, and then the taper of the pot is enough for you to bring the brickwork back in again. I've never had any trouble building the pots in.
The trouble bricklayers usually get is when they don't remove the overailing courses, and have to use slates to hold it in place.
Modern pots are designed to fit straight onto the liners, so you don't get this issue.
I've always thought that building the pots in was a Building reg, and even told a Building Inspector that, but just looked it up and couldn't find it in the regs. However, I found it's a British Standard that the pot, including the flaunching, needs to be either 5 inches, or 25% whichever is the greater.
It's recommended in the textbooks for apprentices is that it's built in 3 courses.

 

[thebadger7]

Thanks all. I think I'll get the pepperpot vents.

Im a bit confused with what size I need (doesn't take much). The pots are 250mm internal diameter, but the vents seem to usually be 190mm spigot size.

These are the pots

Roll Top Chimney Pot Buff

Buy Roll Top Chimney Pot Buff at trade exclusive prices. Shop online with Click & Collect and next day delivery available.

www.selcobw.com

 

[thebadger7]

Ah I guess I need the 235mm spigot size
£75 each and I have 6 pots!