Modern? the internal soil stack was only in use (apart from high rise where
there would also be fire issues) in the 1970s and 1980s.


I have new Selfbuild and this has 2 internal stacks and no external
stacks.

There was a Bld Reg change in early 70's which forced builders to put
stacks inside (knee jerk reaction to a severe winter) .... this did not
last long, and you can put them in or out ... planning permitting.