Chimney DPCs and damp handling

[PeterW]

  On 22/03/2021 at 20:51, MortarThePoint said:

 

You're correct, the stove installer is saying he wants to fit a stainless steel liner.

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WHY..??!! You have a decent pumice liner - why fit something else to it ..?? Stainless liners are for retrofit only in old houses and are not required for a new build where a Class 1 liner has been installed. That is from Hetas..!!

 

If your stove installer doesn’t believe you, print this out and give him a copy - page 7 will help...

 

https://www.hetas.co.uk/wp-content/mediauploads/BFCMA-Installation-Guidelines-10-12-12.pdf

 

Installer is a con artist wanting £300 for a liner you don’t need ..! 

[MortarThePoint]

  On 22/03/2021 at 21:31, PeterW said:

WHY..??!! You have a decent pumice liner - why fit something else to it ..?? Stainless liners are for retrofit only in old houses and are not required for a new build where a Class 1 liner has been installed. That is from Hetas..!!

 

If your stove installer doesn’t believe you, print this out and give him a copy - page 7 will help...

 

https://www.hetas.co.uk/wp-content/mediauploads/BFCMA-Installation-Guidelines-10-12-12.pdf

 

Installer is a con artist wanting £300 for a liner you don’t need ..! 

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It's a fight I've yet to prepare for but think you're right

[PeterW]

Unless he can show the chimney is too large to draw then he has no chance - even then it is down to chimney height usually.
 

What diameter liners have you got installed ..?? 

[MortarThePoint]

  On 22/03/2021 at 21:35, PeterW said:

Unless he can show the chimney is too large to draw then he has no chance - even then it is down to chimney height usually.
 

What diameter liners have you got installed ..?? 

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Isokern 175mm

[PeterW]

So that’s fine - not sure why he thinks it needs lining... 

[MortarThePoint]

Probably so they have full control of the flue path, or because they want the £300

[MortarThePoint]

Well this is what I've produced as drawings:

 

[epsilonGreedy]

Interesting to note we both plan to use blues to visually enhance the impact of the corbel.

 

My pattern going up will be:

 

+20mm corbel

Blue

+20mm corbel

Regular brick

Regular brick

-20mm corbel

Regular brick

Flaunch

 

 

[MortarThePoint]

  On 23/03/2021 at 12:20, epsilonGreedy said:

Interesting to note we both plan to use blues to visually enhance the impact of the corbel.

 

My pattern going up will be:

 

+20mm corbel

Blue

+20mm corbel

Regular brick

Regular brick

-20mm corbel

Regular brick

Flaunch

 

 

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That will look nice. My inspiration on it was reading that two layers of engineering bricks could be used as DPC at the top of the chimney. I'm not so much using it as that but it made me think what it would look like and I think it's nice.

 

A note of caution on blue engineering bricks though. Their colour can be very different manufacturer to manufacturer and indeed batch to batch. I loaded about 10 into the boot of the car before I really noticed they were almost purple. I like the type that when dry have an almost metallic grey shine (Wienerberger Terca). Second note of caution if you aren't aware, make sure you keep them dry before laying as they are a pig if wet.

 

If I were to do it all again, I'd use blue engineering bricks at house DPC level as well.

 

Another note: you'll be getting solid engineering I presume, not perforated.

Edited March 23, 2021 by MortarThePoint

[epsilonGreedy]

  On 23/03/2021 at 13:52, MortarThePoint said:

That will look nice.

 

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I hope so. For others wondering about this, the idea is that a dark course of bricks under a chimney corbel (flare) will trick the eye into thinking the corbel band at the top of the chimney is bigger.

 

  On 23/03/2021 at 13:52, MortarThePoint said:

A note of caution on blue engineering bricks though. Their colour can be very different manufacturer to manufacturer and indeed batch to batch. I loaded about 10 into the boot of the car before I really noticed they were almost purple. I like the type that when dry have an almost metallic grey shine (Wienerberger Terca).

 

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Yes I had different deliveries for the garage and main house below dpc facing bricks and noted both colour types were delivered. Just popped my head outside and the colour difference is not noticeable between the two adjacent structure.

 

My main bricks are buff multi so either colour will work at the top of the chimney.

 

  On 23/03/2021 at 13:52, MortarThePoint said:

Another note: you'll be getting solid engineering I presume, not perforated.

 

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Yup I will ensure they are proper solid engineering bricks for the chimney. Got the perforated type in the main house below dpc, I nearly sent them back when delivered but have forgotten about it now. Regular F2s would have been ok below dpc which means the perforated blues are not a specification fail but they don't seem like the real thing however.

 

  On 23/03/2021 at 13:52, MortarThePoint said:

If I were to do it all again, I'd use blue engineering bricks at house DPC level as well.

 

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It has worked out well for my house design with buff multi elevations. I nearly went for red engineering bricks but then another self build neighbour chose that combination, so my dark dpc band helps mix up the overall picture of the 3 house estate.

[CC45]

125mm liner should be under £20/m incl VAT.  We bought 2 x 9m 125mm liners, 1 x 1000mm, 1 x 500mm & 2 x 45deg bends. £422 + VAT.

[MortarThePoint]

Here's a section through the chimney at its top showing the slate etc. I'll ask them to angle the slates ever so slightly to fall away from the centre of the chimney, but that may be easier said than done.

The 'A' labels what will be blocks cut and packed with stiff mortar.

 

Edited March 24, 2021 by MortarThePoint
corrected drawing corbel

[PeterW]

Never seen slate inside a liner - pot is normally larger than the liner and you flaunch the inside too. 

[epsilonGreedy]

  On 24/03/2021 at 09:45, MortarThePoint said:

Here's a section through the chimney at its top showing the slate etc

 

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You are good at knocking up these diagrams, do you do this in your job?

 

Re. the height of pot support, I make that 250mm including the flaunching. Is this amount of pot support recommended? I ask because it results in a lot of material up there that might hold moisture.

[MortarThePoint]

  On 24/03/2021 at 10:03, PeterW said:

Never seen slate inside a liner - pot is normally larger than the liner and you flaunch the inside too. 

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It is on the outside. My second image probably wasn't put into context well. It's a closer look like this:

[MortarThePoint]

  On 24/03/2021 at 11:04, epsilonGreedy said:

 

You are good at knocking up these diagrams, do you do this in your job?

 

Re. the height of pot support, I make that 250mm including the flaunching. Is this amount of pot support recommended? I ask because it results in a lot of material up there that might hold moisture.

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Thanks, I use two cheap tools QCAD and PowerPoint. Very different to the day job, but useful to convey the details.

 

Yes, as conceived the pot is embedded by minimum 225mm. This is embedded 150mm in the cut blocks and mortar ('A'). Most of this is below the upper layers of slate though so will hopefully not get too moist.

Edited March 24, 2021 by MortarThePoint

[MortarThePoint]

I'm getting confused about the second lead tray on the other chimney now which is going in tomorrow. I have had both trays made large enough to extend out of the brickwork and lap up or down the brickwork by 75mm. I definitely need that for the first tray that is mostly within the roof space. On three sides of the chimney, that first tray will be lapped up the brickwork and on the fourth side it will lap down the brickwork. That puts the apron a brick course below the last bit of stepped flashing on the sides of the chimney.

I've convinced myself somehow that the second tray is supposed to lap down the outside of the brickwork. However I have seen various diagrams online that seem to show it stopping at the edge of brickwork so not actually coming out and lapping onto the outer surface of the brickwork at all. Which is correct? I have drawn the two options below as viewed from the side of the chimney.

 

It's a bit difficult to tuck the lead flashing in below the tray in the right hand approach. I guess the tray could come out wherever the flashing meets it, highlighted red here:

Edited March 25, 2021 by MortarThePoint

[MortarThePoint]

Have you had to work this out for your chimney @epsilonGreedy

[epsilonGreedy]

  On 25/03/2021 at 22:32, MortarThePoint said:

Have you had to work this out for your chimney @epsilonGreedy

 

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I am not that far ahead. I thought I read in this thread or viewed a Peter Scholey video where he shows the tray with a short 35mm or 40mm upturn on three sides and a downturn on the main wall side.

 

Jump to 4 minutes 35...

https://www.youtube.com/watch?v=AAdcYazFIio

 

In general I wonder if you are trying to create cover flashing out of the tray in error. This next PS video shows an independent rear gully cover flashing fitted over the back gully lead, note how it wraps around the sides and over the side step flashing. I doubt your lead tray flaps would do this so well.

 

Jump to 6 minutes 50...

https://www.youtube.com/watch?v=5lov8yAFI-I

 

Thinking about your situation some more is it legit to tuck the top flange of the cover flashing under the full tray in the same brick course? We need an expert to answer that.

 

Edited March 25, 2021 by epsilonGreedy

[MortarThePoint]

  On 25/03/2021 at 23:24, epsilonGreedy said:

In general I wonder if you are trying to create cover flashing out of the tray in error. This next PS video shows an independent rear gully cover flashing fitted over the back gully lead, note how it wraps around the sides and over the side step flashing. I doubt your lead tray flaps would do this so well.

 

Jump to 6 minutes 50...

https://www.youtube.com/watch?v=5lov8yAFI-I

 

Thinking about your situation some more is it legit to tuck the top flange of the cover flashing under the full tray in the same brick course? We need an expert to answer that.

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Is there anything wrong with using the tray to form the cover flashing? There may not be enough lead to reach down 150mm though, probably just 75mm. This is from the LABC technical manual and looks to be showing the tray forming the cover flashing:

 

I wondering is @PeterW knows if this is OK or if the top flange of the cover flashing can be tucked into the same bed as a tray.

[MortarThePoint]

Well the main chimney is finished, then had to rush to try and save the flaunching from some rain which has resulted in some minor damage. A shame, but I guess you seldom see the top of a chimneys flaunching and it's more important that it is weatherproof. Here's a photo after I enacted a repair (approx. 3 hours after the rest of the flaunching was finished and in the half light). The perspective of the photo makes the pot look massively off centre, but it is in the centre.

 

The second chimney is up to the level of the second lead tray. The tray is placed on to protect the brickwork from any rain before it's finished. I'm still liking the hybrid approach of having the tray sticking out around the back and part of the sides (shown red) and folded down over the flashing. Round the front and part of the sides cut back to flush with brickwork.

 

[Mr Punter]

Looks good.  Quite a hassle to plan and build.  How much do you think it cost per chimney?

[PeterW]

  On 27/03/2021 at 08:38, MortarThePoint said:

Well the main chimney is finished, then had to rush to try and save the flaunching from some rain which has resulted in some minor damage. A shame, but I guess you seldom see the top of a chimneys flaunching and it's more important that it is weatherproof. Here's a photo after I enacted a repair (approx. 3 hours after the rest of the flaunching was finished and in the half light). The perspective of the photo makes the pot look massively off centre, but it is in the centre.

 

The second chimney is up to the level of the second lead tray. The tray is placed on to protect the brickwork from any rain before it's finished. I'm still liking the hybrid approach of having the tray sticking out around the back and part of the sides (shown red) and folded down over the flashing. Round the front and part of the sides cut back to flush with brickwork.

 

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wrap over is fine - bead of lead seal would help keep it watertight on the overlap 

[MortarThePoint]

  On 27/03/2021 at 11:13, Mr Punter said:

Looks good.  Quite a hassle to plan and build.  How much do you think it cost per chimney?

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Thank you. It has been a challenge to get my head around. Haven't really focused on the cost so much as it feels like such an integral part of the house. The liner system was £1464 for two chimneys.

 

Above roof level: the brickie spent about 4days 1:1 so that's another £1200 or so. Bricks above roof level were about 800+200=1000 so around £650. Blocks probably £150.

 

Below roof level: the brickies probably sent 4 days 2:1.5 so that's about £2200. Extra bricks over being just wall probably around 400+700=1100 so around £700. Blocks probably around £250. Lintels around £250  (Naylor R9 £93 and Supreme R21?£130?). Extra footings probably around 7m3 so around £850. Probably additional truss cost of around £150.

 

Total: £7864 so call it £8k

 

So that's £4k per chimney before even connecting a stove to it. Probably looking at £5-6k all finished.

[MortarThePoint]

  On 27/03/2021 at 11:53, PeterW said:

wrap over is fine - bead of lead seal would help keep it watertight on the overlap 

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Thanks. Do you like the approach of having it half lapped and half flush? Viewed from above, it means the tray has to be cut to this shaper where the green portion ends up embedded in brickwork and the orange portion sticks out to then get bend down over the flashing and back gully.