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Chimney Question


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2 hours ago, PeterW said:

Top section doesnt need block and you need to lose the 50mm cavity around the fire back as before. 

 

Thanks Peter ..

I hope i have drawn it right this time (fingers crossed)

 

I have changed the Section B up ....and when i look on youtube i see that many divide this up into sections 

(presumable for strength ..or int eh case of multiple flues.

 

As i only have one (in the middle ...how should i handle the WASTE space ..should i infill the X's with various

hardcore and mortar available ...i do have a LOT

 

I could leave the whole chimney ..open (as its not really being used anyway) ...but would that make it structurally weak ?

 

*i have removed the blocks from the top section of the chimney

but wasn't sure if it still need a cavity of sorts 

 

Chimney_Layout_Ed_Rev4.pdf

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thanks Peter.

 

Its a bit tricky that ....the SE has advised i need an RSJ on padstones just under it...

these in turn are resting on 20mm of Dense concrete blocks, 2 wide. these fall outside the 

wall line obviously ..So I will need to work out how to draw that or the top section will have a step 

back towards the house ..if you see what i mean . I will work on it

 

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I was thinking (sometimes i do) ...whilst the chimney is being built

would it be prudent to basically "build around a temporary pipe" to leave a hole

for the flue outlet later at the back of the chimney ?

 

Also regarding external flue height ...and safety (sorry I have never had a flue)

is there a position recommended? ...height from ground ? ...something like that ?

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46 minutes ago, Ed_MK said:

I was thinking (sometimes i do) ...whilst the chimney is being built

would it be prudent to basically "build around a temporary pipe" to leave a hole

for the flue outlet later at the back of the chimney ?

 

Also regarding external flue height ...and safety (sorry I have never had a flue)

is there a position recommended? ...height from ground ? ...something like that ?

 

Has to meet gas regs in terms of position but I would just build blank and then core drill the flue at a later date - neater and easier. 

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OK Peter tx,

 

I have played around this afternoon ..setting things up to get an idea.

PS. I know this is not the right insulation material ....but it was lying around so i used it for width reference.

 

As you can see factoring in the 7N blocks to carry the internal beam mantle and the exterior RSJ

total Wall thicknesses Face to Face ...are

 

Sides = 500mm

Back = 400mm

 

will this cause issues with the horizontal part of the flue do you think ...as after it leaves the Huntingdon and goes upwards to its

"elbow" ..I am guessing it will have to be apx 700mm to get to the exterior 

 

fp1.jpg

fp2.jpg

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Hi Peter,

the engineer is sending me the calcs on Monday/Tuesday.

but he told me in advance the RSJ to order so I would have it ready

 

his calcs were based on the RSJ being supported for at least 15cm on eiother side 

on 7.3N dense concrete blocks ...hence the double wall

 

Padding the insulation to 100mm all around shouldn't be an issue...except it will leave

it with a rather narrow "throat" ....but still capable of getting a flue up and over.

 

the issue I am struggling with is the narrow chimney that runs upwards after the inglenook narrows.

Obviously the FACE has to line up with the face of the lower outer fireplace...but i recall you saying 

"single wall" from thee upwards would suffice ..

 

 

But i cant seem to get my head around how this will reconcile/join with the lower section...obviously

as its a fake chimney ....some sort of "capping" inside perhaps to close off the lower section ? 

 

 

Also ...I know you are right about the 100mm of insulation around the chimney. the majority of the house appears to be using a 50mm

Kingspan Panel ...so chimneys need more ?!?

 

Edited by Ed_MK
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If the majority of the house is 50mm you’re in for epic fuel bills and probably an automatic fail for building regs ..!! Aren’t the panels full fill..??

 

What steel has he suggested ..?? And there is a better way to do that fireplace so you get both insulation and structure... 

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With regards to insulation, our builder has suggested a specific type due to the problems of getting it into the cavity with all the "ties" we have up the structure. He says rigid would not work so has suggested "compressed" glass fibre strips.

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Not sure why he wants to insulate between a masonry chimney and the vapour layer of the frame ..?? If anything I would want a cavity here as it’s probably the most likely spot for water ingress (at the top) so I would want it open 

 

 

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52 minutes ago, PeterW said:

Not sure why he wants to insulate between a masonry chimney and the vapour layer of the frame ..?? If anything I would want a cavity here as it’s probably the most likely spot for water ingress (at the top) so I would want it open 

 

 

 

Hi  - I think he is looking at the cavity between the block work rather than between the block work and layered TF - Should have made that clearer first time round - sorry

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  • 3 months later...
11 minutes ago, dpmiller said:

Just re-reading this one and I've a query- is there any reason why the inner skin of this kind of buildup (my own is somewhat similar) can't use thermal blocks?

 

No issue at all although it’s the bridging from TF to the masonry that causes the issue. It leaves an open cavity that needs to have a tray over and also a potential cold bridge. Got any sections ..?

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Right then just waiting on some drawings from Schiedel, WRT using their Ignis Protect to bring stovepipe through the TF and into the Swift Air. Means I can just build a TF panel to fill in the current gap (w/ stud centres to suit the Ignis)and plunk it into place. 200mm masonry alcove freestanding on the inside for the stove, and all airtightness, insulations and cavities intact.

 

Sounds like a winner?

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  • 1 month later...

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