Stove pipe install through airtight structural timber frame wall

[Hastings]

I need to install a stove pipe at an angle, out through a timber frame airtight MVHR build wall, and on through 150mm rubble stone, joining 5" flexi-liner fitted in an existing old chimney.

 

The wall make up (inside to out) is not unusual:
12.5 p/board,
45mm woodfibre insulation,
Intello+ membrane (the airtightness),
100mm woodfibre,
11mm OSB3,
Solitex Fronta roof membrane,
50mm gap,
700mm old stone gable wall with chimneys (flexi liner already in place).

 

My thinking is that in effect, I treat the wall as it were a roof:

 

I get two standard EPDM rubber/aluminium roof flashing boots to fit around twin-wall pipe and tape the aluminium plates to both membranes, leaving a 5-8cm (depending on manufacturer) air gap distance to everything else including the plasterboard?

 

Probably give support/fixing to the first aluminium plate by inserting 2x2 noggins between studs. The outer flashing plate probably can be screwed to the OSB.

 

Finally, cover the decorated plasterboard/skim gap with a shiny oval metal cutout plate you can buy for such eventualities?

 

Local builder who has already installed the flex-liner joined it onto 6" single walled pipe coming through wall into the living room (leaving it for me to build the t/frame up to and around shortly), but that seems to go against everything I have read about stove installations and I assume will need to be replaced.

 

Thanks in advance.

 

Edited September 5, 2020 by Hastings
photo added

[ProDave]

I used an insulated sleeve sold at flue-pipes.com

 

 

This was for a roof penetration.

 

By definition, because it was sold as such, it must be made of a non flamable material so is okay touching the twin wall flue pipe.  And it is okay for anything flamable to touch the outside of the sleeve as that then meets the minimum distance from the flue to flamable materials.

 

So you would seal your air tightness layer to the sleeve.

 

Problems you need to solve:

 

It needs to be twin wall not single for this.

 

How to join the twin wall to the liner up the chimney. Would that need to be done in such a way that it can be inspected?

[Simplysimon]

is the horizontal section the intake pipe? and as above as @ProDave says, dig into wall a bit to make connection to twin wall to keep single wall away from anything flammable.

[Hastings]

1 hour ago, ProDave said:

How to join the twin wall to the liner up the chimney. Would that need to be done in such a way that it can be inspected?

 

It's going be very hard to design for inspection of that joint. Is that a regs requirement?

 

Thanks @ProDave for the heads up on the non-combustible collar - looks perfect.

 

18 minutes ago, Simplysimon said:

is the horizontal section the intake pipe?

Yes. But it was also put there for venting of the wall cavity (which is open to the cold roof void) - I am thinking it is simpler to supply air to the stove from the cavity (which has multiple vents to outside around 3 sides of the house) as I have read that BC allowed for @ProDave 's installation.

[Hastings]

If I wanted to complete the installation with the single-wall flue pipe as it is on the photo above, how would I do it? Just would like to know why it was done that way.

 

When it was done (a year or so back) I didn't pay much attention. I was just very relieved that the liner went in okay without needing to open up the gable wall to clear blockages, and is why I got it done before the stonework became inaccessible behind the timber frame. 

 

I just took it that it was correct because I had gone to the expense of hiring someone to do it that could provide a certificate when all done.

[ProDave]

If the person that installed that flue pipe is going to issue a HETAS certificate, let them finish it.

 

The issue become the distance you must maintain from that flue to combustible materials, and how you would seal it all to maintain your air tightness.  For a twin wall insulated flue that distance is typically only 50-60mmm but will be much greater for a single wall flue, something like 3 times the flue diameter? 

 

Perhaps you could bring a section of stone wall out to finished wall level as a feature behind the stove?

 

Stoves in general like a warm flue, so I would not like to say how well it would work with what I suspect will be a very cold flue (i,e, no insulation)

[Nickfromwales]

9 minutes ago, ProDave said:

 

If the person that installed that flue pipe is going to issue a HETAS certificate, let them finish it.

 

+1, as you’ll be on their insurance then also. 

[Hastings]

Hmmm. Just checked the HETAS register and he is not listed. Nearest one is 50miles, as a crow would fly across the sea to the mainland.

Trying to avoid asking Building Control as I already have other questions for them that have gone unanswered for many months now.

[Hastings]

1 hour ago, ProDave said:

Perhaps you could bring a section of stone wall out to finished wall level as a feature behind the stove?

 

Stoves in general like a warm flue, so I would not like to say how well it would work with what I suspect will be a very cold flue (i,e, no insulation)

 

Really prefer not to interrupt the insulation envelope, particularly so close to the only heat source in the house.

 

in fact I wondered about increasing the insulation behind the stove, using the unused void of the old fireplace.

 

Another idea: building inside the insulation envelope an entire concrete block wall, as a thermal store.

 

The chimney flexi-liner is fairly/partly insulated with that stuff you pour down around it from above. But there must have been a hole linking to another flue because it wouldn't fill entirely to the top.

Edited September 5, 2020 by Hastings
2nd thoughts

[dpmiller]

to go through the timber frame on ours I used these:

 

https://www.schiedel.com/uk/products/additional-ranges/ignis-protect/

[Hastings]

9 minutes ago, Hastings said:

Another idea: building inside the insulation envelope an entire concrete block wall, as a thermal store.

 

A cheap DIY version of masonry stoves as used in Scandinavia.

[PeterW]

On 05/09/2020 at 16:46, Hastings said:

Hmmm. Just checked the HETAS register and he is not listed. Nearest one is 50miles, as a crow would fly across the sea to the mainland.

Trying to avoid asking Building Control as I already have other questions for them that have gone unanswered for many months now.

Just on this you will need to plan for how you would remove the liner to replace it in future. That requires access to both ends of the flexible liner, and it looks like you will only have access to the top..?

 

I think you may need to remove a couple of joints before continuing, potentially replace the 6” through the wall with 8” and route the liner through this.