Cutting a long story short , I have rehashed a large bathroom, corridor into a bedroom and bathroom. New bathroom is c 12*5 ft, the bath [ cast iron c 40+ years old]?has been moved and runs parallel to the joists rather than across. In the midst of this work we encountered 3 joists with dry rot near the pan and basin. So these have been rectified with 3 new joists sistered, bolted, treated new tongue and groove fitted. We also made consideration for this bath to sit in the middle of two joists , given we had to keep the floor cut open due to the level of the floor and flow etc. Hey presto see pic , it’s a fair bit of and bath is not even sealed in. V Annoyed owner at my builder!!!! Who is out of the equation! Solutions : Build out wall to make sure bath sits on joists- lose c 5” Or run steel plates screwed across the joists and allow the bath to sit there or maybe weld into position both extreme I know!! Board up with t&g from joist to joist to spread the Weight and put a bend in the waste to allow the flow and notch out accordingly. Remove stretch of board below in kitchen and run in joists! NB. Tiler decided to run his hardibacker board ahead of the plumber setting the bath today!!! The joists are 5*4 sistered up with 5*2 with struts at 12ft span so pretty solid. The door is 30” and can be reduced to 28” although Iam about 1” spare here. See pics: blue lines is wear the joists are running and yellow crosses where the noggins have been put in place with ( spare c16 7*2) red circles show the obvious where the legs are barely hitting the support! Advice? Hope to get some good responses as new comer. I am good with calcs if someone can point me in the right direction, but issue is the joists are non standard. Assuming dead load +live load / area of bath = knm2 ? Against trada figs? Thanks in aniticipation .