Building Regs question: Double skinned metal flues

sas · 11-10-2010 10:07AM #1

Hi,

If I'm reading the homebond book correctly I need to leave 150mm from the outer skin of my metal flue to the nearest combustible material. Is this correct?

So a flue with external diameter of 200mm, results in a 500mm hole with the flue dead centre.

This is a bloody nuisance from a windtightness point of view. A nuisance I will have to live with I would like to underline (assuming I'm correct).

Does this distance also affect the slating battens, i.e. do they also have to fall 150mm from the flue? The only way I can see to achieve this is to use an oversized vulgar lead flashing collar. The flue is on the front of the house so this isn't ideal.

Thoughts or suggestions?

CJhaughey · 11-10-2010 11:13AM

I wouldn't work to Homebond regs, I can't see them lasting much longer TBH.

newmug · 11-10-2010 11:15AM

CJhaughey wrote: »

I wouldn't work to Homebond regs, I can't see them lasting much longer TBH.

Why, will the regs get worse or better?

CJhaughey · 11-10-2010 12:07PM

Homebond will itself be gone IMO.

sas · 11-10-2010 12:56PM

Thanks for feedback so far.

As I understand it, the homebond book mostly illustrates the building regs that were in place when it was published. Homebond don't create regs.

I'd like to be wrong here.

CJhaughey · 11-10-2010 02:38PM

AFAIK it is 50mm

homewardbound11 · 11-10-2010 04:13PM

I am trying to remember my own situation but homebond specifically reference twin walled flues and their manufacture to BS standards. They also recommend that you follow your manufactures guidlines.
My twinwall flues specified to have 80mm clearance to combustables and with solid firestops with airtight seals from proclima, this solved my airtightness at ceiling level. Your roof level is easily accomodated with a flue colar for the pitch of your roof and then your normal lead flashing and storm collar etc.

I went through the hoops also and found that the external temp of your twin walled flue will not be above 80 degrees. So your material for airtightness will need to be spec'd for this rating. EPDM is the material that will go around your twin wall at your airtightness layer. Google it and you should have your answer.
I hope my information is good for you but this is exactly the same issue i went through and found the above to be the solution. You would wonder with all the airtightness that this hasn't came up before.
Best of luck..

sas wrote: »

Hi,

If I'm reading the homebond book correctly I need to leave 150mm from the outer skin of my metal flue to the nearest combustible material. Is this correct?

So a flue with external diameter of 200mm, results in a 500mm hole with the flue dead centre.

This is a bloody nuisance from a windtightness point of view. A nuisance I will have to live with I would like to underline (assuming I'm correct).

Does this distance also affect the slating battens, i.e. do they also have to fall 150mm from the flue? The only way I can see to achieve this is to use an oversized vulgar lead flashing collar. The flue is on the front of the house so this isn't ideal.

Thoughts or suggestions?

reefray · 11-10-2010 07:38PM

sas

a 50mm gap is all that is generally required from combustibles incl slating lath.
rockwool-type insulations are non-combustible. this means you can insulate tight to your flue.
there are a choice of these with rockwool and knauf both providing options for you.

ray

tfer · 11-10-2010 09:52PM

I am building a timber frame house, and was thinking of putting in a room sealed inset stove, (with a twin walled flue) in the living room, can I build the chimney out of timber as long as I keep the gaps ye have mentioned.
My chimney has to be on the inside, so say the planners. Thanks in advance

homewardbound11 · 11-10-2010 10:45PM

Hi,
You can build a mock chimney for your flue off the timer at rof level but not a conventional block chimney. I am almost sure there is a company in clare that sell them. They are mock chimneys for astetics only but will do the trick for you.

Check homebond a 40mm gap is from conventional block chimney systems. The homebound does reference the suppliers of twinwall for distances to combustables.

I dont have it at the moment to hand but homebound dont cover twinwalll as well as standard constructed breasts. It does reference single wall and its distances from combustables to be 3 times the diamater if there is no heat shield. You will have to check this with your engineer signing off the build . I remeber i was totally paranoid about this but my engineer put my mind to rest and did reference that my free standing stove and twin wall was not as a conventional system in homebond.

ComDubh · 07-11-2010 12:28AM

We'd a stove with a twin-lined flue going through the wall of our timber-framed house. 50mm from the timbers, covered in rockwool and installed very professionally as far as I can see. After a few months of use it set the wall on fire and we're lucky we found out before the whole house burned or worse. Building regs may seem OTT in many cases, but I would take a belt and braces approach if I were doing it again.

martin46585 · 07-11-2010 12:45PM

reefray wrote: »

sas

a 50mm gap is all that is generally required from combustibles incl slating lath.
rockwool-type insulations are non-combustible. this means you can insulate tight to your flue.
there are a choice of these with rockwool and knauf both providing options for you.

ray

the 50mm gap must be maintained at all cross sections, the idea of filling it with any type of insulation is wrong, it is this practice and that of unvented boxed in flues, that cause the flue to over heat and start a fire,
in most cases the home owner is unaware as the fire is in either a boxed of section of a closest or in the roof space.

Building Regs question: Double skinned metal flues

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