It was due to effort involved (having to chisel joists etc...) We did drop the waste in the end, and fortunately (or unfortunately) Roger the Bodger who owned the house previously had the too long (with too many joints) waste pipe running upwards towards the soil stack. We used less joints and a shorten pipe and we didnt have to mess around with the soil stack : )
Can any one answer 2 questions please?
---> Does it make any difference when fitting a shower tray if the waste goes to the front or the back?
---> Also is there any disadvantages for using a high density foam shower tray as opposed to a stone cast one?