Non vertical Soil Stacks

[Hennycare]

I am working on a project where a (proposed) internal Soil stack clashes with a partition. It is being proposed that the stack is vertically offset from the vertical by ~5 degrees (300mm over 3.3m).
I am struggling to find anywhere within CIBSE / BS that mention offsets from the vertical. Does anyone have an insight into this?
My instinct is that a few degrees don't matter, after all many builders have cast in positions off between floors and it hasn't caused issues.

So does anyone know:
What angle for a straight running stack is permissible (if any?) or is it down to the BCO?
Should it even be mentioned to BC? OR assumed to act as a vertical stack?

Thanks.

 

[John D v2.0]

Approved docs say supposed to be vertical with minimal offsets in the wet part, but i can't see how an offset and vertical would be better than a steady slope from a performance point of view. Practically
you'd have to watch out for cross flow as you aren't allowed to enter the stack on the lower half with a smaller pipe or even a bigger one if you couldn't get a fall, and all your tees and other fittings would come out at the wrong angle unless you went in the side rather than the top or bent them down a bit.

 

[OvertonPlumber]

Why not just keep the soil vertical and dogleg it with 2x 90s around the partition?

 

[polesapart]

A few degrees off vertical will not affect stack performance.

Preferable to introducing 135 offsets IMO.

 

[Hennycare]

Thank you for the speedy responses, to add to some clarity here is a nice section. There is a strengthening beam forcing the offset. 2 90 degree corners would IMO be a recipe for blockages. There shouldn't be any cross flow as all waste will be coming in from North or West (if that makes sense, 90 degree max entry to each other).
To complicate things it is proposed to be ventilated with an AAV as it is for a triplex apartment with flats above...
The stack is to have connections on all three floors, which I am of the understanding complies with Code.

Anyone have any further comments to dissuade or commend this to being a sensible (enough) proposal?

Thanks again.