"Christian McArdle" wrote in message et...
What size joist should I go for?, one book I read says I can use 100x50mm
(4x2) but I`m not sure.

A 47mm x 97mm joist on 400mm spacings with SC3 timber and 0.25-0.5 kN/m2
allows a span of 1.92m, making it just compliant with building regulations.
If you had wanted a bath installed, you would double up the joists
supporting it.

Spookliy enough, I'm probably about to do something very similar;
building a raised floor in bedroom 3 (formerly bathroom) to enable
soil pipes etc from what will be an internal bathroom to reach the
external wall. (I can't see any other way of doing it given the
layout of the house and joists etc).

What I was going to do was essentially nail new joists parallel to and
directly above the existing structural joists (not sure whether its
worthwhile/necessary to remove the floorboards first - may do so just
to ensure I can see any hidden wiring/pipes!). The soil pipe will be
traversing the structural joists diagonally (which is why I can't
'bury' it below floor level), so the new timbers will just have a gap
where the pipe goes through. (This is upstairs in a terraced house
BTW).

Given that my new timbers (I hesitate to call them joists, cos they
aren't!) are not a structural part of the house as such, I was going
to use much less substantial wood for them than the real joists; just
using my common sense. Or is that wrong - do I need to fulfil any
building regs by using stinking great 5x2's? Would it make a
difference if I left the original floorboards there or not?

Thanks
David