Chimney Works

[Feltwell]

"Never seen the like" - you want to see what they've put on the new builds near here Doug!

So these houses are your typical new build estate, all squeezed on like crazy to the smallest plots imaginable with naff all parking, then sold at grossly over-inflated prices to gullible people who think they'll have no problems as they're new. (I'm not keen, can you tell?? )

I wouldn't say built so much, more thrown up as quickly as possible. Anyhow, the "chimneys" on the roofs are pre-fabricated timber framed boxes, clad with fake brick effect panels and with what looks like a plastic chimney pot on top, that is plonked on top of the roof trusses before the tiles go on. They serve no purpose at all - no flue of any kind goes to them. As for flashing, it's a lead free zone here - the roofing membrane passes right under the "chimney" and it looks like some kind of pre-fitted corrugated aluminium flashing is bent down over the tiles.

Back to lead though - with that very tall and slender chimney I've got on the side of my house, I'd be concerned about a DPC compromising the structural integrity - i.e. introducing a weak point in the masonry that could cause problems if a storm was trying to push the stack over. As it is now I'm not concerned, it's managed 120 years so far!

[88v8]

...had a HETAS engineer out today, between us we smoke tested the one flue that I want to reinstate an open fire too, good news is that it's sound and no need to line it - so that's about £1k saved (liners for use with coal are more expensive than for woodburners apparently - and it's a *very* tall house).

Mmm, three points; yes, smokeless fuel needs a higher grade of liner because the flue gases are corrosive. So, not that it applies to you but if one were to fit a lower grade liner for a woodstove and then start burning smokeless fuel in it, the liner would corrode and eventually disintegrate.

The second point is that if the house is tall, the liner may need an interim support. Especially with a newfangulation of powered sweeping which introduces a dynamic load into the liner. The interim support means cutting a hole into the flue, either from inside or outside.

And the third point is that a tall liner may have too much draw for the stove.
The HETAS guy should measure the draw on the flue and determine whether it will he excessive. You may also need to consult the proposed stove manufacturer. Over 30ft might be an issue.
Excess draw can be controlled by a barometric damper.
https://directflues.co.uk/stove-pipe-st ... all-5-inch
Note: this is 5". You'll need 6" which I'm sure they can get for you, and make you an adaptor so it will sit on your stovepipe.
We have one on one of our stoves, it made a huge difference to controllability.

In times of yore they would have had lots of nice hot flue gases going up them in the colder & wetter months, which must have helped. Nowadays most flues are redundant and those that are in use are often lined, which must cut the drying effectiveness down.

Indeed. The lack of air flow through a lined flue makes a huge difference to its dryness. In our case the difference between water pooling in the fireplace, and completely dry.
To create airflow in a lined flue, drill holes into the flue near the top of the stack, four x 1" will do, and cover them in stainless insect mesh to keep bees out.
Then, at the bottom, insert a couple of vents into the register plate. Now you will have air going up the flue, which will keep it dry.

Ivor

[overlander matt]

Nice work on the chimneys Feltwell and helpful reading ahead of the work on two stacks starting next week. Thanks for posting in so much detail.

I have a few questions (as always!) on the subject - we have octagonal, buff-coloured pots on our chimneys which look to have a few small holes in and I wondered about the best way to repair these while the pots are removed. I managed to pick up a spare pot at a reclamation yard too which will be used to replace a broken red coloured imposter. We also plan to fit flue liners to four flues which I requested in a application to the CO at the local council but I have not specified any cowls - the main problem here is that I have not seen any that actually look any good in this colour - has anyone any recommendations for a more discrete option? Possibly I will need to consider painting one...

I'm also interested about insulation for flue liners. I've not insulated flues in previous houses which have had wood burners and wondered whether this is appropriate in a period property.

Final question on your job Feltwell, how did you clean the brickwork after the repointing? I recently posted about cleaning up brickwork and the general consensus was it was not a good idea but when there is staining post pointing it does make sense to me.

Thanks again.

Matt

[Feltwell]

Hi Matt

Repairing pots - not had to do any here, but with a liner inside them (which should go to the top of the pot) they are decorative more than anything - so fill holes however you like. On a buff pot 2 part epoxy wood filler would do the job I reckon, get the natural colour Ronseal stuff and it may well be about the right colour.

I don’t know much about liners - I’ve heard of folks pouring vermiculite insulation around liners, I do wonder if that is a good idea as without it you’d get some air flow outside the liner to help keep the old flue drier.

Brickwork cleaning - I’m no expert but I gave them a good scrub with a scrubbing brush and a hosepipe twice - then went over again carefully painting acid onto each brick and rinsing it off quickly. Might depend on the bricks but it worked well on these, they are very hard though.

Flue cowls - I don’t think painted ones would look good for long. I haven’t worried about it too much, redundant flues have a pepperpot cap on them, live ones I’ve gone for a stainless anti-bird cowl, attaches to the pot with a long jubilee clip.

Hope that helps

[88v8]

I'm also interested about insulation for flue liners. I've not insulated flues in previous houses which have had wood burners and wondered whether this is appropriate in a period property.

I've painted an alloy cowl (Brewer UFO 2 ) black. With appropriate prep of the alloy, heatproof primer & paint I think it will last well, so far seven years. Paint designed for car exhaust manifolds has suitable characteristics.

Flue liners can be jacketed. The insulation jacket is put on before the liner is lowered into the flue. We have two here, being thatched they are de rigeur. Completely reversible.

Ivor

[overlander matt]

At last the scaffold has reached the first chimney and we've been able to take a look at the state of it...

On the pots front, one has got a couple of good size holes which will need to be repaired. The holes are north facing strangely enough - I would have expected greater weathering from the west but perhaps they have been turned in the past. There does not appear to be too much mortar holding them on and decent gaps around each pot. There's not much (any!) mortar lining within the chimney either which I'm surprised about. When I've removed chimney stacks in the past there has been plenty of mortar lining the flues. Is this just a matter of this being a tall stack outside the building?

I will have a look at the Ronseal epoxy for wood - that could be a good match. As for caps or cowls, I'm still not sure what will work well with the octagonal pots. I suspect it will be something round and in need of a coat of paint.

Chimey pots.jpg (238.82 KiB) Viewed 1055 times

[Westholme]

At last the scaffold has reached the first chimney and we've been able to take a look at the state of it...

On the pots front, one has got a couple of good size holes which will need to be repaired. The holes are north facing strangely enough - I would have expected greater weathering from the west but perhaps they have been turned in the past.

Is the pot with the holes over the fireplace that was probably used the most? Pots can be eroded away from the inside by flue gases.

There does not appear to be too much mortar holding them on and decent gaps around each pot. There's not much (any!) mortar lining within the chimney either which I'm surprised about. When I've removed chimney stacks in the past there has been plenty of mortar lining the flues. Is this just a matter of this being a tall stack outside the building?

McKay's Building Construction states that the flue lining or parging should continue up into the chimney stack, changing to waterproofed cement mortar one foot below roof level, but perhaps this was omitted in your case.

[overlander matt]

We put the flue liners in today which was fairly interesting... One which will connect to a woodburner was left uninsulated and the other for the boiler stove was insulated using the tubular rockwool sections. This was a tricky exercise pulling the insulated liner up the flue but we got there in the end.

Flue liners.jpg (226.62 KiB) Viewed 992 times

Talking about the end, we are wondering about the most suitable method of supporting the flue at the chimney end. The flue was supplied with a support bracket that clamps on the flue and can be supported by the brickwork of the chimney but it looks a bit flimsy and I will most likely beef this up (not with a blue rope though). The suppliers recommended a metal plate to seal the top of the flue. I would have thought this was counterproductive from the ventilation perspective. Do you have any recommendations? Every time I come to install a woodburner (every 5 years) it seems there is something new to consider.

The insulated flue is 11m long and the uninsulated is 8m. I noted Feltwell's comment about providing an additional support lower down the flue. The insulated flue feels pretty well supported but the uninsulated one is just dangling!

Another decision is needed on the cowls. I have 5 flues that are unused and need a ventilation cowl and 4 with liners. The octagonal shape of the pot complicates this - the internal diameter at the top is 225mm and the external is 275mm but the round profile of the chimney only extends for 30mm from the top before it takes on its octagonal shape which doesn't allow much for the cowl supports to be strapped on with the long Jubilee clip.

Another point to report - using a two part wood filler has done a great repair job on the pots.

Thanks for any ideas on this or recommendations on the cowls.

Matt

[Feltwell]

Would a buff pepperpot chimney cowl not do the job for the unused flues Matt? They're not fixed in place, just sit there under their own weight.

I've 5 on various chimneys, been there for 13 years with no problems.

https://www.aboutroofing.com/clay-peppe ... black.html

Re. supporting the liner - no, that wasn't me, the 8m uninsulated one I've just installed is on a pot hanger only. Doesn't weigh much though and it's hard down against the bottom of the flue anyway. Eventually, when a stove is installed, it'll be supported from below.

Top of the chimney - not entirely sure what you mean. I supported the pots on metal bars across the brickwork, either side of the flue liner (where there was one), at the same level as the bottom of the edge stones, so the metal bars went under the edge stones. Then I filled the gaps around the pots with pieces of slate, again at the same level as the bottom of the edge stones, prior to filling in & flaunching over the top - really the slate is there just to give support until the flaunching goes off.

Flaunching by the way is one area where I do use cement - it gets such a hard time with the weather and has no need to be breathable. I mixed mortar using mostly sharp sand, with an SBR admixture (which aids bonding and waterproofing) and with fibre reinforcement mixed in - a bit like a concrete equivalent of hair in lime plaster, helps stop cracking. Not very period but it is an area where I think a modern harder material is justified.

[Feltwell]

Would a buff pepperpot chimney cowl not do the job for the unused flues Matt? They're not fixed in place, just sit there under their own weight.

Hmm - actually - having been up the scaffold to my newly refurbished chimney in the rain today, a little of the rain running off the top of the pepperpot cowl has been entering the chimney pot. Not much at all, but enough that a bead of silicone sealant around the joint is worth doing I think - only silicone, so it can come apart easily in future (not like neighbour's ones that have been Gripfilled! )

[88v8]

Talking about the end, we are wondering about the most suitable method of supporting the flue at the chimney end. The flue was supplied with a support bracket that clamps on the flue and can be supported by the brickwork of the chimney but it looks a bit flimsy and I will most likely beef this up (not with a blue rope though). The suppliers recommended a metal plate to seal the top of the flue. I would have thought this was counterproductive from the ventilation perspective.

The insulated flue is 11m long and the uninsulated is 8m. I noted Feltwell's comment about providing an additional support lower down the flue. The insulated flue feels pretty well supported but the uninsulated one is just dangling!

Another decision is needed on the cowls. I have 5 flues that are unused and need a ventilation cowl and 4 with liners. The octagonal shape of the pot complicates this - the internal diameter at the top is 225mm and the external is 275mm but the round profile of the chimney only extends for 30mm from the top before it takes on its octagonal shape which doesn't allow much for the cowl supports to be strapped on with the long Jubilee clip.

As I may have mentioned, I used the Brewer UFO2.
To attach it to our very similar octagonal pot I used stainless wire, ran a loop around the top of the pot under the lip and wired the cowl to the loop. It ain't going anywhere.

Long runs of loose liner aren't a great idea. Especially now that sweeps tend to use a power sweeper which can make the liner move around a lot. So Feltwell's point about an interim support is a good one.

It's customary to close the top of the flue with a plate, also helps to support the clamp. That insulated liner is heavy and it will be supported mainly from the top.
But yes, it's counterproductive from the ventilation perspective.
So, to give continued ventilation in the flue, I drilled four x 1" holes through the stack near the top, and covered them with stainless bee mesh. Then at the bottom I have a slot about an inch wide along the back of the register plate, so there is a constant through flow of air in the stack.
That has worked well in drying what was a wet stack, so wet that in bad weather we had pools of water in the fireplace where rain was getting in through defective pointing somewhere under the thatch. And no doubt is still getting in, but the ventilation nullifies the problem.

Ivor

[Feltwell]

Finished chimneys 2 & 3, scaffold coming down tomorrow!

Some Before 'n' Afters:-

[Feltwell]

.

[88v8]

Whoever did that pointing could give Matt's builder a lesson

Good for 100 years.

Ivor

[Feltwell]

100 would be great but I'll settle for 50 - definitely won't be my problem after then! I'll put a couple of close ups on Matt's thread.

Good to see the scaffold gone. The chimneys are quite a dominant feature of this place, hopefully their future is now secure for a good number of years. Now we've just got the rest of the house to repoint!