Oh dear! Can the flue squeeze in here?

[Jimbo37]

Hi all.

I seem to have snookered myself, but maybe (hopefully) there is a way around it...

I have a stove planned for my living room, with a flue going straight up through the ceiling into the bedroom wardrobe space above, and on through the roof. Installer had planned on using Dinak DW or T600 flue, but...

 - 125mm flue outer diameter is 175mm

 - Receommended clearance between flue and combustibles (joists), 60mm

 - Space between joists (in first floor), 285mm

So that suggests that my joists are 10mm too close for this to be compliant?

 - Can I solve this problem with a heat shield on one side (I think a heat shield needs 25mm circulation, but what are they and how thick are they?)

 - Any other flue system/brand that may squeeze in here? Related - is that 60mm clearance a manufacturer recommendation or a regulation?

(The roof joists are wider spaced, so this problem just exists at first floor level)

Thanks, James

Edited August 31, 2023 by Jimbo37

[Mr Punter]

Could you get a piece of 10mm fireboard on the side of the joists where the flue goes up?

[Jimbo37]

3 minutes ago, Mr Punter said:

Could you get a piece of 10mm fireboard on the side of the joists where the flue goes up?

Thanks @Mr Punter - would that need ventillation behind it? Would it address the regulation issue, or is it just a good workaround?

[Mr Punter]

I may have misunderstood but I thought that screwing fire board onto the side of the joists would mean that the joists were no longer flammable and the 60mm clearance would not apply.  You would end up with about 40mm between the flue and the fire board at the tightest point.

[Jimbo37]

OK, now that sounds promising, and Ill check it out - I can get lots of fibre board

 

[Jimbo37]

A related question, please - when is T600 required, as I see more frequent reference to T450?

[Mr Punter]

40 minutes ago, Jimbo37 said:

OK, now that sounds promising, and Ill check it out - I can get lots of fibre board

 

 

Fire resistant board, like Promat, Glasroc, Supalux, cement boards etc.

[dpmiller]

Give the nice folk at Schiedel NI a call, I think they do a Protect Box for this kinda thing and should be able to spec the whole system.

[ProDave]

Why have you only got 285mm between joists?  That is awfully close.  What sort of joists are they?

 

This is a theoretical problem, i.e. you need some form of making it conform to a set of written regs.  I have the same flue (with ample clearance) and from practical experience when the stove is on, even after burning for a long time, the flue is only warm to the touch, and I swear in the real world a piece of wood in contact with the outside of that twin wall flue would most definitely not come to grief.

 

 

[Jimbo37]

16 hours ago, ProDave said:

Why have you only got 285mm between joists?

Just the two last joists, all others @400mm

 

16 hours ago, ProDave said:

This is a theoretical problem

Agreed, but I have to comply - peace of mind, insurance, eextreme situations, etc

[ProDave]

44 minutes ago, Jimbo37 said:

Just the two last joists, all others @400mm

That's a shame.  If only the joists has started at the other end with the odd space where it does not matter.

 

Move the stove over one joist so the flue goes up through a wide gap?

 

What sort of joists?  If like ours, posi joists, the very end one is really a "spacer" between the downstairs and upstairs timber frame, it half sits on the frame and half overhangs the room, so it is not actually working as a joist.  I feel certain with input from a SE that one could have a chunk cut out if it needed to.

 

Picture of the joists and the offending too small gap?

[Jimbo37]

52 minutes ago, ProDave said:

Move the stove over one joist so the flue goes up through a wide gap?

Not possible, coz Id be moving it a foot into the room, not along the wall.

52 minutes ago, ProDave said:

Picture of the joists and the offending too small gap?

Positioned twoards the left of this pic - the white beam is for room wall above, and flue rund up in that corner of upstairs room

[joe90]

How is that OSB floor fixed? If screws can you not remove them and move the joist over a bit? How much too tight is the flue? If a small amount can you not move just one end the small amount required?

Edited September 1, 2023 by joe90

[ProDave]

I feel certain a SE could specify a new joist sistered onto the side of that joist, with lots of bolts, and then a section of the offending joust cut out where the flue is going through, to give you another 50mm or so.

[Jimbo37]

On 01/09/2023 at 13:06, ProDave said:

I feel certain a SE could specify a new joist sistered onto the side of that joist, with lots of bolts, and then a section of the offending joust cut out where the flue is going through, to give you another 50mm or so.

Yes, had a chat, for the benefit of others that may find it useful, in my own words

 - span is 4.5m
 - 600mm to be removed from one end
 - 1.6m to be spliced in, to give a min of 1m overlap
 - 4 x 12mm bolts staggered off centres, and double faces toothed plates/washers between

 

Also, as it happens, an easier solution may be available, based on @Mr Punter comment

 - 12mm fibre board, mounted to on 25mm fibreboard spacer to give 25mm ventillation behind

 - to reduce the required clrearance by 50%, ie from 60mm to 30mm (but subject to the stove guy agreeing that I got this right)

 - so 125mm flue, with 175mm outer diameter plus 2x30mm - giving a total required space of 235mm

 - which should all fit between the 285mm joist space (and a bit to spare)

Thanks all for your comments, tips and advice

Edited September 4, 2023 by Jimbo37

[ProDave]

Thanks.  Lets us know which solution you go with.  And pictures of course.

[saveasteading]

Do you mean fire board, or fibre board? @Mr Punter says fire board, but your message says fibre.

I suggest you make sure the bco is ok with the fire board method before committing....maybe you have already. I say this having once had a right barney with the bco, who wouldn't accept that timber was non flammable when protected by cement board. (His argument was that timber is a flammable material....end of argument) He did eventually and very reluctantly give way (4 storeys of timber stairs didn't  have to be replaced). Best agreed early.

[joe90]

26 minutes ago, saveasteading said:

had a right barney with the bco,

Another example of no consistency with building control.

[Big Jimbo]

19 minutes ago, joe90 said:

Another example of no consistency with building control.

Yeah , but thank heavens for that @joe90 There are some many things within the building regulations that conflict with each other, great to have them onboard and trying to work out solutions with you. I have had some great debates with BCO's over the years. 

[saveasteading]

3 hours ago, joe90 said:

no consistency with building control.

This was inconsistency within the bco system. The local LA had been chatting me up to give them a go again. 'They had changed'.  So we did, and they delegated site visits to the LA where the project was.   2i inspectors with different opinions, and double the list of queries. It was clear that one of them wasn't used to being challenged.

 

We went back to private inspectors.

 

[saveasteading]

On 04/09/2023 at 19:43, saveasteading said:

Do you mean fire board, or fibre board

 

[Jimbo37]

@saveasteading sorry, just noticed this. Fire board.

[Jimbo37]

On 04/09/2023 at 23:42, saveasteading said:

This was inconsistency within the bco system. The local LA had been chatting me up to give them a go again. 'They had changed'.  So we did, and they delegated site visits to the LA where the project was.   2i inspectors with different opinions, and double the list of queries. It was clear that one of them wasn't used to being challenged.

 

We went back to private inspectors.

 

 

On 01/09/2023 at 13:05, joe90 said:

How is that OSB floor fixed?

Nailed, unfortunately, but still a possibility

[Jimbo37]

On 04/09/2023 at 18:58, Jimbo37 said:

Also, as it happens, an easier solution may be available, based on @Mr Punter comment

 - 12mm fibre board, mounted to on 25mm fibreboard spacer to give 25mm ventillation behind

 - to reduce the required clrearance by 50%, ie from 60mm to 30mm (but subject to the stove guy agreeing that I got this right)

 - so 125mm flue, with 175mm outer diameter plus 2x30mm - giving a total required space of 235mm

 - which should all fit between the 285mm joist space (and a bit to spare)

This is what I'm doing, but with a 300x300 frame above, made from 50x50 batten on top - so as to comply with ventillation. Will need approval of stove installation guy who is on holidays till Wednesday. Will post with pics, if we clear the compliance hurddle

[Jimbo37]

Picture of as-built, which has had approval from the stove installer - see detail ablve, summarised as follows

 - heat shield with 25mm ventillation behind on one joist to reduce required clearance to combustion from 60mm to 30mm

 - collar above, made from wood at allowed regular 60mm clearance (heat shield comes into this space, but stops 25mm short of top, to allow ventillation as normal

Thanks everyone for your assistance - jobz a gud un!