Tiling upstairs toilet floor + soil pipe query


Two questions:
1. If floor tiling on top of floor boards which are currently prone to slight flexing, what is the best material and thickness for a sub-floor to go on top which can then take the tiles?
2. I need to do work on the soil pipe to place the loo in a different position and cater for the increased height of the floor. The soil pipe is boxed in internally (i.e. exists through the roof) and from the outside, looks like metal up to the vent cap.
Because of the combination of manifolds, resin bonding etc. and the inaccessible position, I think I am going to have to cut the boxed in soil pipe from the hall below, and let a new section in with the required branches and manifolds at the correct height.
Could someone explain to me exactly how the plastic soil pipe exits through a roof? I'm kinda hoping it is like an outer sleeve and the plastic pipe is free to slide up inside it a bit, allowing me to introduce the new joints without any work being done on the roof.
Failing that, my only other idea was if it is possible to get a plastic sleeve for soil pipe so I could chop out (say) a 3ft section above all the manifolds, make the changes I need to, then replace the section and bond the sleeves over the joints.
TIA Midge
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Minium 19mm / 3/4" ply

The soil pipe should lift up through the Lead slate or soil pipe collier, providing it as not had any glue or tape binding the two together and fixing clips in the boxing in. The hard part is parting the soil pipe at the joint

Quite right

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Thanks Keith - I think I'm clear on the pipe clips as the roof slopes down to that corner.
You're right about the joint though - the manifolds/branches are really difficult to get to and I suspect are resin jointed. I can't get anywhere near to cut under the joint either as it's tight between joists. Hense my conclusion I may have to cut through the pipe from close to the ceiling in the hall below.
I have a nasty suspicion that even if the soil pipe does move upwards, I may still not get the 18 inches of movement I need to get the manifold/branches out, so a cut-n-shut might end up being te only way.
Cheers, Midge.

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try this for the soil pipe/roof problem
http://www.diydoctor.org.uk/projects/air_admittance_valves.htm

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Thanks for the idea Eric.
Midge.

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