Another badly planned project on my part then. I'm not sure what other
options I have and the shower & tray is arriving tomorrow. I thought that
it
was safe to put holes in the joists providing that a) it was close to the
supporting wall and b) the hole went through the middle of the joist and
c)
the diameter of the hole was no bigger than two thirds of the joist?

Also, I was planning to put a slight incline on the run through the joists
to provide this.



I have just looked in a plumbing manual (from 1995) - it says holes cannot
be bigger than 1/4 of the depth of the beam and the zone in which they can
be made is between 0.25 and 0.4 of the length of the beam from wall.
Also,the holes must not be below the centre of the beam or closer than 3
times the diameter to any other holes.

Dave