Woodburning stove & chimney design... will it pass regs?

[jongreen]

My local building control are happy for me to install my own woodburning stove, and they'll sign it off within their fee - provided it meets regs.

So, I've designed it, but will it pass? Here's my design, any thoughts, constructive criticism or total freakouts from knowledgable DIY'ers or pros would be most welcome.

Notes:

- The 1m section of twin wall that intersects the roof is already installed with rafter supports, storm guard and flashing. That needs to stay (or be moved at great expense).

- The stove spec
-- 5kw output
-- Suitable for 12mm hearth (does not reach 100 degrees underneath)
-- Distance to comustibles 700mm
-- Distance to shielded combustibles 350mm
-- Distance to A-rated non-combustibles 100mm

Thanks!

Many thanks!

 

[Doggit]

If the twin wall pipe wasn't already in the roof, then I'd have suggested you go out through the wall.

You don't need the fibreboard at the back as a wall isn't combustible. See if you can take out the 150mm piece in the bend 117207, and then you can move the stove back a bit.

It would be better to bring the 45 degree bends lower, and the flue can be secured to the wall for more stability.

 

[jongreen]

Thanks for the advice Doggit. The wall is plasterboard with skim over a timber frame. I was under the impression that plasterboard is considered to be 'combustible'. Is that not correct?

I've also seen advice regarding bends, that they should be at least 600mm above the stove output to provide optimum draw. Is that not right either?

 

[Doggit]

Sorry Jon, I didn't spot the stud wall, but as the distance to shielded combustibles says 350mm, then should you move it further away. I'm not an expert at twin wall, so apologies until the experts come along, but I would still try and get more support against the wall, and what are you doing on the roof. Are those 500mm sections, which should still let you take out one of them to lower the internal bend, in addition, does the stove have access to the flue from inside the stove (normally does) and that should let you take out the inspection chamber. I've had a look at the ICS installation notes, and would definitely say you need someone better than me here, but I'm glad for the chance to learn.

 

[jongreen]

That's it, I'm not sure whether the Vitra A-rated Fireboard is classed as a 'shield' or as 'a-rated' when placed over the stud wall. So that's one area I need clarity on.

Good point about the inspection chamber, I'll check with stove manufacturer.

And you're right about the bend, I could still lower it and add support if necessary. Question is, is it really necessary? The stove will presumably take some weight, as does the rafter support. The external sections are the ones I'm more concerned about, do I need outriggers up there?

Any experts out there? (I imagine they're all busy installing stoves for wiser people).

 

[Doggit]

You don't want the roof and the stove taking the weight if it's a twin wall system, as they're not exactly lightweight once you start adding sections together. Likewise, once it gets out of the roof, it's going to get battered by the winds, and will put a strain on the exit point from the roof, and you risk getting a leak, so depending on the wind conditions near you, I'd go for outriggers as a matter of course, as it's easier to fit them now, than do repairs later.

 

[jongreen]

Ok, good advice. I'll do that. I do live on the coast in Cornwall, so there can be some pretty hefty winds.

 

[lostinthelight]

The stove will presumably take some weight, as does the rafter support. The external sections are the ones I'm more concerned about, do I need outriggers up there?

Any experts out there? (I imagine they're all busy installing stoves for wiser people).

There shouldnt be any weight on the stove, the weight of the flue should be carried by rafters and or wall supports.
You need to check with the flue manufacturer for the specs for how much you can have waving about above the roof before additional support is needed as it varies between them.
Have you made provision for fire stops and if you close off the ceiling before the BI can inspect it you should take pictures of your instalation.
litl

 

[jongreen]

Thanks lostinthelight. I did wonder about firestops, the roof and ceiling are pitched, excuse my ignorance, but where do I need to put the fire stop(s) exactly?

 

[jongreen]

A little further reading on the structural support for ICS shows that the rafter support can bear the weight of 6m of 150mm twin wall ICS. (this setup is only 4m in total) And lateral support is only required at 4m intervals. The rafter support presumably counts as lateral support as well as load bearing.

You are right about the guy wires though, I do need one at 1.5 meter intervals above the roof (one guy wire bracket will cover this).

Any further thoughts on the distance to combustibles issue? Is the A-Rated Fireboard over plasterboard considered a shielded combustible, or is it a-rated?

 

[rssteve]

You need at least 2 supports on the chimney to stop lateral movement.

 

[jongreen]

Ok, thanks Steve. I'll add one internally.

 

[Doggit]

One guy wire will only provide support in one direction, 2 will stop it moving backwards and forwards, but not sideways, but with 2 supports internally, may suffice, but you may not get 2 set internally, so set it down just above the bend.