Chimney Question

[Ed_MK]

It is for me Peter ...

top be honest with the heat i didn't sleep much last night 

and i went out back with my maglite at 3am to do some more exact measurements ....am i mad ?

...possibly!

 

anyway i sad down with some graph paper and i will be finished soon and let you see it ..

I THINK I have cracked it ....going with your recommendations for cavity and what space i have to work with 

using the RSJ..Tx

 

the only bit I cant seem to get my head around is where the chimney "narrows" ..i.e at the top of the first floor it stats to
come into the actually upper chimney width ..

 

Now with the RSJ and the other walls supporting all 4 sides below ...I think we are on the money ...Boom!

 

But (unless I am being anal again!)...when the span gets narrower ....at this junction does that not change the load bearing 
from the edge of the outer chimney walls to nearer the centre?

 

i looked online and they seem to show bricks "stepping" up with a large overlap ...but surely this wont carry the weight of that side of chimney

say 200 bricks or more away to the edges? ...or is this some engineers mystery that just "works"

 

I will show you what i mean ,......its basically this side (and the opposite one)

 

I know this is not my chimney  ...but it was best example of pic i could find in first 7 pages of google images !

 

 

 

 

`

 

hang on ...I have just found the below on dunbrik site 

...is this the hidden secret weapon ??? ...but it only says 1m wide...:(

 

and i was thinking it would be something that fit across the very TOP of the wide bit
and right across to take all the weight from the slope  to the edges ...like a bridge and 

a start for the flue pipe in ONE

 

...ok , my bad

 

 

Edited July 8, 2018 by Ed_MK

[Tennentslager]

Is that not called a register plate.

In my basic reading, researching for a brick chimney for a timber hut, the register plate is often bespoke and made for each application.

As far as I understood, this makes up the horizontal plate which provides a fireproof barrier above the stove AND takes the weight of the structure above.

They are normally made of thick steel with a hole cut to accept the stove flue.

I guess being (expletive deleted) off thick steel, it's no problem to mount any type of chimney liner on top.

No expert, and, not sure I understand but my tuppence worth if it helps?

[PeterW]

Look at the square dunbrik stove block. It’s 565mm square from memory. 

 

Back wall fly over the RSJ and where the chimney is it will have a pair of side walls built up from the sides of the stove block. 

This gives the basics of the square chimney and you then build up around the chimney gable as normal. 

 

This leaves the two sloping areas that are causing me the questions about how to finish those and to close them off ..!! This would give a flat ceiling to the chimney alcove which is better than a sloped alcove as that needs much more work including how to insulate and fireproof any timber structure for the slope roof unless you go for the costly and difficult stepped brickwork that needs a lot of planning to get it right. 

 

The external bit is easy, the internal bit is a pain ..!

[Declan52]

You can use a concrete flue gather to start it off. 

Build the two sides with a block on it's flat up to what ever height you want it to be. The concrete flue gather sits on the first 4 inches of each side. 

From then on you can take it up to the ceiling and once you get there step it in so it's only a block square right round. 

Flues are built in as you go and filled with vermiculite when it's harden.

As it's block the complete way up it will be suitable for a timber frame build.

Remember to put a  2 bends on the flue to help draw smoke. It will either draw smoke or tears and you want it to be smoke.

https://fpmccann.co.uk/chimney-caps-flue-gatherers

[Ed_MK]

On 08/07/2018 at 21:45, PeterW said:

Look at the square dunbrik stove block. It’s 565mm square from memory. 

 

Back wall fly over the RSJ and where the chimney is it will have a pair of side walls built up from the sides of the stove block. 

This gives the basics of the square chimney and you then build up around the chimney gable as normal. 

 

This leaves the two sloping areas that are causing me the questions about how to finish those and to close them off ..!! This would give a flat ceiling to the chimney alcove which is better than a sloped alcove as that needs much more work including how to insulate and fireproof any timber structure for the slope roof unless you go for the costly and difficult stepped brickwork that needs a lot of planning to get it right. 

 

The external bit is easy, the internal bit is a pain ..!

 

I agree Peter!...I know we have been talking in message about this ....but I finally see what you mean.

For others

....it is a TF Frame with a 50mm Cavity Faced off in Brick

....The lower 9-11 courses have a "plinth" and under that it is "Brick and Brick on Edge" to get extra width for plinth stand-off

...no problems wit the plinth me thinks ...

 

Now I can draw this Chimney area easily and it has the same structure as the wall too ...plinth, face and even put in the 50mm cavity

Of course this cavity will now be between Brick (Outer Skin) and Concrete Common ..but it will still go all around ...good ? 

 

The issue here is the where the chimney abuts (is that a word) the building...

 

For strength I was thinking that the planned RSJ/Lintel  (which would carry the weight of the chimney wall up the building) would need to be
fixed SOLIDLY to the TF itself,  ...via copious L Arcon Ties ?

This would of course KILL the cavity above the lintel effectively

 

i.e.  Inner chimney course upward from there...would have no cavity ...basically in the below image it is the area that shows

the fixing points.

 

Oh ...and the Rendered area ....which will be done later on ...does have a "stand off" on renderboard from the TF ...not sure now much. but of course it would be 
"beaded" where it is to meet the chimney..I presume

 

I mean it is drummed into us ...Cavity, Cavity ...CAVITY !!

 

But in a case like this ..is there any alternative for this area where we could ADD ..something, a barrier or something ...and kill the cavity ?

 

I mean the chimney itself ...Tall Run is NOT humongous...externally it could be as narrow as we wanted .....but as the wife wanted a twin pot 

(God knows why ..its only a gas fire) ..,it will probably end up with external dimensions of 1000 x 450 ..so slightly FATTER as you look from side elevation

 

 

Edited July 11, 2018 by Ed_MK

[PeterW]

Right....

 

minimum depth from the TF is going to be 600mm from the front of the chimney as you need 250mm for the liner, 200mm for the bricks and 100mm for the vermiculite all round (50mm each side) and then your 50mm TF cavity. 

 

Good news is 550mm for the chimney works bricks so thats an easy one. If you really want 2 pots then one is a blank; chimney will need to be 1050 wide to cope with the liner and the pot at the top.  That’s a big chimney ..!!

 

cavity will need trays and some clever detailing to close the cavity to drafts

 

Other issues include getting some insulation between the brick skins ...

[Ed_MK]

Might have to convince HTMBO ...to drop the 2nd chimney pot  ..if its going to make it look like Windscale ..and cause more headache for me..and you guys helping me !

 

I wish I never heard the words "twin-wall" , "RSJ" and "dunbrik liner" LOL

 

So I have taken your advice above ....and have altered my sketch

 

In the below pic ..does THIS solve our problems

 

YELLOW - Concrete Bricks supporting the  lintel now tied on edge into a course running upward flush with TF to close the Cavity and hence the draught into lounge?

 

PINK - A bloody Wide DPC curtain, Lead sheet (whatever is best) ...Tucked under the Kingspan Outer insulation (by cutting and inserting and nailing back)
this will then run all the way across the chimney are and be fixed well around the liner cirecle  ..basically sealing any water from coming down the cavity and channeling it 
away to the outside skin

 

RED - 4 - 5 "weeps set into the outer and side face brick ....so that any water collected by the DPC/lead curtain is allowed to drain away 

 

have i cracked it ....or am I just crackers ?

 

 

 

 

[Redoctober]

@Ed_MK Not sure how advanced you are with teh chimney but as I mentioned previously, ours started today and these photos may be of assistance. 

 

The basically show the external chimney being constructed in block work, a cavity and then the blocks on which the external stone will sit on and rise up from. The chimney has been constructed so that it sits flush with the internal panels of the TF.

 

 

[PeterW]

32 minutes ago, Redoctober said:

@Ed_MK Not sure how advanced you are with teh chimney but as I mentioned previously, ours started today and these photos may be of assistance. 

 

The basically show the external chimney being constructed in block work, a cavity and then the blocks on which the external stone will sit on and rise up from. The chimney has been constructed so that it sits flush with the internal panels of the TF.

 

 

 

So how are you insulating that cavity ..?

 

otherwise you have a monumental cold bridge through that corner. 

[Redoctober]

8 minutes ago, PeterW said:

 

So how are you insulating that cavity .. 

otherwise you have a monumental cold bridge through that corner. 

 

Good point @PeterW What are my options ?

[PeterW]

59 minutes ago, Redoctober said:

 

Good point @PeterW What are my options ?

 

Only real option is pull down that external skin and move it out to give you 100mm cavity. Then full fill the cavity with rock wool and wrap it past the edges of the block onto the TF. 

 

What chimney system are you using ..?

[Nickfromwales]

1 hour ago, PeterW said:

 

So how are you insulating that cavity ..?

 

otherwise you have a monumental cold bridge through that corner. 

Has the BCO accepted that ? 

[Redoctober]

38 minutes ago, PeterW said:

 

Only real option is pull down that external skin and move it out to give you 100mm cavity. Then full fill the cavity with rock wool and wrap it past the edges of the block onto the TF. 

 

What chimney system are you using ..?

 Thanks. I will know more in the morning as the guy doing the internal bit and the WBS installation will be in site.

[CC45]

we did what @PeterW suggested.

 

If you use a concrete liner / rings make sure you used the correct one to start with - my brickie balanced it on a few blocks (on top of some lintels) - complete pain in the arse to connect the stove to this - this headache hasn't been fully resolved yet.

 

Pictures 4 & 5 here.

 

http://www.selfbuildselfhelp.com/Advice/DoingStuff/ChimneyFlue2.htm

[Ed_MK]

Some good advice and pics above ..

I wish my chimney was that narrow ...its ridiculously big (at the base anyway 2.5m!)

Potton design.

 

I have a brickie coming in 2 weeks and wanted to get the design and stuff sorted out by then, including anything i need to buy
liners? perhaps ...it is only a gas fire but ...

 

PeterW has been guiding me on things like cavities and insulation , and I think like you above ...I would be better of building in block 

and then cladding the face on after 

 

Its just getting the internal structure right ...As the top 4m of stack will be almost freestanding as it is separated by the cavity up the outer wall

...makes me kinda nervous 

[Ed_MK]

Also..

 

I have just finished extending some of the RIDICULOUSLY SHORT pipes left by the groundworkers ...some of them were actually 1" protruding from the base
So i had to get a breaker to get enough room to get a collar on them and extend . the do look OK and fall is looking good ...they are only Kitchen wastewater ...not 

Toilet ones

 

One thought ...Due to the position of another pipe (installed by the groundworkers, running under sunroom) ..I have had to hug the wall to get a connection to it..
..but I am left with about 180mm of Trench block in which to lay bricks on ....(including cavity) ...Now the brickwork and cavity are only 150mm, but the bottom several courses have a plinth on ...and this takes it out to around 215mm...so slightly OVER the pipe in places by about 10mm-20mm. Will i be OK ?

 

I know the obvious answer would have been to go lower and bridge ...But I am SEVERELY challenged by Fall to connect to an existing long drainage run, any deeper and i would have been pumping

 

 

 

Edited July 17, 2018 by Ed_MK

[Onoff]

Assuming you'll need short lintel over that pipe.

[Ed_MK]

hmmm... the only issue is that the foundation literally ENDS under the outside edge of the pipe...
..i will think of something.

 

going back to my chimney (the one i haven't got yet)

..it looks like it is trickier than i thought ...but i want to get it right 

.....but in reality ....DO I REALLY NEED A LINER, DUNBRIK, TERRACOTTA RINGS  OR OTHERWISE ???

 

as its only a gas fire and the BCO mentioned Stainless Steel Twinwall? ...would that not suffice ?...I see
stuff on the internet that describe themselves as "pot hangers" ...

 

its just if i can get away with leaving a straightforward rectangle hole all the way up and using one of those ,

...potentially saves me £1000 in a lining system that would never get any warmer than a cold crumpet anyway 

 

[PeterW]

14 minutes ago, Ed_MK said:

DO I REALLY NEED A LINER, DUNBRIK, TERRACOTTA RINGS  OR OTHERWISE ???

 

Yes to meet building regulations. 

 

14 minutes ago, Ed_MK said:

the BCO mentioned Stainless Steel Twinwall? ...would that not suffice

 

Can only be used externally or where each joint can be inspected (comes in up to 2m lengths) so can’t be built into masonry

 

14 minutes ago, Ed_MK said:

stuff on the internet that describe themselves as "pot hangers"

 

Thats for re-lining old chimneys - you would still need to build the stack and pay £3-400 for a decent liner

 

 

14 minutes ago, Ed_MK said:

its just if i can get away with leaving a straightforward rectangle hole all the way up and using one of those ,

...potentially saves me £1000 in a lining system that would never get any warmer than a cold crumpet anyway 

 

 

I’d buy a very good carbon monoxide alarm and put it in the room as that a is a recipe for killing someone. 

 

I would give serious thought to making the chimney decorative and using a gas stove with a through wall terminal as was previously suggested 

[Nickfromwales]

Nothing stopping you fitting a closure plate in the breast and just running a flue liner to the chimney pot ? 

6 hours ago, Ed_MK said:

Its just getting the internal structure right ...As the top 4m of stack will be almost freestanding as it is separated by the cavity up the outer wall

...makes me kinda nervous 

Say that bit again. 

Your stack isn't tied into the structure? Is it off a hip so no structure parallel to tie to ?

4m !

There's a gap between the two ?

Who designed the chimney ?

[PeterW]

1 minute ago, Nickfromwales said:

Nothing stopping you fitting a closure plate in the breast and just running a flue liner to the chimney pot ? 

 

Decent stainless gas liner with correct closure and hanger etc will be £300 plus, and then the GSR has to install the liner as it becomes part of the installation so scaffold needs to remain. So add £250 plus scaff costs for fitting ... 

 

Built concrete liners with the correct sealant between are exempt as they are deemed structural so do not require an inspection by GSR. 

 

But  my money would be to spend on a  balanced flue gas fired log burner. Something like the Gazco Huntingdon 40 would fit perfectly and it can be routed up above the inner lintel so it “looks” like a proper stove and then out the back of the chimney breast and you will never notice it. 

[Nickfromwales]

Yup, after making a 2.5m feature fireplace a tea light may look out of place . 

After the balanced flue exists, cant this be closed off so all your space heat doesn't just bugger off up to the clouds every hour of every day for the rest of your life? Cap and closure and external vents for convection for the remainder of the stack? Might as well have fitted a fridge there otherwise. 

[epsilonGreedy]

6 hours ago, Ed_MK said:

Also..

 

I have just finished extending some of the RIDICULOUSLY SHORT pipes left by the groundworkers ...some of them were actually 1" protruding from the base
So i had to get a breaker to get enough room to get a collar on them and extend . the do look OK and fall is looking good ...they are only Kitchen wastewater ...not 

Toilet ones

 

 

Interesting. I purchased a secondhand cement mixer last weekend from a pro brickie who was getting rid of his 240v equipment after a run-in with health & safety.

 

We got talking about my selfbuild and he stressed this very point about not skimping on the height of pipework upstands emerging through the unfinished floor. Shame on Potton for cursing you with that team of groundworkers.

[epsilonGreedy]

I see the OP is getting loads of quality structural advice so instead I thought I would chip in re. lifestyle.

 

First I think the big wide Potton statement fireplaces are great and it is worth surmounting the structural challenges to achieve the end result. The 1800 sq ft Potton "cottage" demo house in Sandy is a testament to how good this can look.

 

Where I would caution the OP is on the gas stove focus. I put a gas stove in a proper class-1 chimney and regretted that decision for 12 years. For the last three years I have lived with a proper fire and there is no comparison. This hiss of the gas delivery does not match the random sound track of a proper fire while reading the Sunday papers on a winter afternoon.

 

I would prefer to have 10 proper fires a year than 50 gas fire click-start experiences. My now started selfbuild will have two working chimneys and a 3rd false one, which reminds me I need to start researching what block floor widget I need to draw air up from the void into a wood burner stove.

Edited July 18, 2018 by epsilonGreedy

[Ed_MK]

1 hour ago, PeterW said:

 

 

But  my money would be to spend on a  balanced flue gas fired log burner. Something like the Gazco Huntingdon 40 would fit perfectly and it can be routed up above the inner lintel so it “looks” like a proper stove and then out the back of the chimney breast and you will never notice it. 

 

that is EXACTLY the one the wife wants Peter

although we are swaying between the 30 and 40

 

and still trying to get our head around the CF versus BF bit

 

but i hear your post above ....either way we are into a liner ...looks like back to Dunbrik config page again