Twinwall Flue install - Rafter clearance problem

[gez777]

Hi All,
I hope someone can advise me on a twinwall Flue install I am doing on my bungalow.
I will be getting the Building Control guy in to approve the work before I start but would like to have an idea as to
what he would expect to see done. I am looking to install a Woodburning Stove in a downstairs room and want to
route the flue internally up through the Ceiling, into the eaves space and out the roof.
I have limited clearance to the left hand rafter as you can see below:

So I propose to cut this rafter and install trimmers to support the structure. I am limited on access (it's a 1m x1m eaves crawl space) so
can't get to the top purlin but could go lower down on the wallplate and 'birdsmouth' the trimmer onto that if necessary.
The timbers are 2"x4" and I would be using structural screws and PVA to connect the trimmers.
I have drawn out a couple of options and wonder if one of the roofing guru's here could comment or perhaps suggest a better option.

If I move the flue as far right as I can I could probably get away with this as clearance,
I can't get up to the purlin but could extend the trimmer down to the wallboard for extra support if necessary. Do you think this would satisfy the BCO?

If not another option perhaps?
As my bungalow is mostly flat roofed this structure is only supporting a side roof so no great weight on it,
I just would like to know if I would be OK to cut out the middle rafter prior to getting in the trimmers (if I went with the below option)
or am i better to extend the left and right hand most trimmers to the wallboard, before I cut out the middle rafter and then add the top and bottom and extra inside vertical trimmers after?

Hope this all makes some sense.
Many thanks, Gerry.

 

[Bilabong007]

Hi Gerry,

Not that I know much about the content of your post, but I thought I would say welcome to the forum and for a first time post that's some great detail and pictures you have given.

No doubt someone here will be a long soon with the answer.

Graeme

 

[Nige F]

2 offset bends in the flue might move it over enough and up the slope of the roof. Those big joists are a PITA - is it a chalet bungalow they look like floor joistsl

 

[gez777]

Yep, well deducted Nige F, it is indeed a Chalet Bungalow! I did look at using two offset bends (a couple of 30 Degree ones look like they might do
the job, but might also give me Joist clearance issues on the right hand side) so I was a bit reluctant to shell out the £150 or so if i didn't end up being able to use them.
I did a bit more thinking and came up with another idea: Extend the trimmers down to the wallboard and 'Skew' Structural Screws into the frame as in yellow below.
Blue is normal countersunk screws to hold cut ends and the inner trimmers and slather PVA on everything.

I can go down low and 'birds-mouth' my side vertical trimmers onto the wallplate, but as the purlin is inaccessable
I would have to finish my vertical trimmers high up on the rafter, but not reaching the purlin. Below pic shows (lack of) access:

In the end all I want to do is gain clearance and support the middle cut Rafter safely to gain aproval from the BCO.
The part of the roof this structure supports is fairly small (as the Bungalow has a main Flat roof) and it consists of the
45 degee slope formed over the 4 foot wide x 4 foot high eaves crawl-space, so no great weight is being supported.
Please advise if I am 'skew' fixing badly/to much/too little and whether you can see a better(simpler) solution.
Thanks, Gerry.