In article ,
"Kevin" says...
As I am approching the completion of the extension I have been working
on for far too long, I have started to think a little more about using
some of the extra space which I now have in one of the bedrooms. It
had long been in the back of my mind that we might put an en-suite
shower/wc in. My original thought was that I would run the soil pipe
parellel to the first floor joists between ceiling and floor, out
through the wall and then across the back of the house to connect to
the existing stack.

Last night I had one of those moments when you suddenly realise that
it wont work the way you have been thinking about from the start. The
snip

Why not build a raised floor and hide all the plumbing under it?