Bathroom joist notches

[Daddy Boots]

Refurbishing the bathroom and had a nasty surprise when I lifted the floorboards.
http://home2.btconnect.com/dublydublydubly/PhotoAlbums/album_1306180433/
The joists are 7x2 with a couple 7x3 , at 16 inch centres with a 10 feet span.
The pic is the worst notch, 3.5 inches wide and 2.5inches deep smack in the middle of the span, the rest of the notches are 2 inchx2 inch. the waste is 35mm from the basin and becomes 40mm after the T. It's been like this for at least 20years, with no signs of sagging.
I'm planning to install underfloor heating with ceramic tiles on top and the bath will most likely go where the basin/shower is currently installed. Can I use a 40mm waste for the bath and more importantly, what should I do about the notches ?
seems to be 3 options:-
1. Attach 5 inch joists to the existing and bolt through
2. Attach metal plates to either side and bolt through
3. Attach metal strips to the underside as suggested in this post by brickeyee:-
http://ths.gardenweb.com/forums/load/repair/msg0915531723856.html The problem with 3 is the lath and plaster ceiling below has intricate coving and ceiling rose that cannot be disturbed.
The additional support/reinforcement will need to be sufficient to support the ply/underfloor heating/screed/ceramic tiles. If that can't be achieved then I suppose another option would be to put the new bath/shower/2 basins/wc/bidet on plinths to allow the drainage on top of the existing floor.

 

[Lower]

Sister the joists to 500mm either side of the notch and bolt through if you're worried.

The fact that there has been no movement means that the joists are probably strong enough, even if the notch is bigger than it should be.

Are you going to replace the floor with ply? If you lift all the boards and replace with 25mm wbp ply screwed down either side of the notch you will increase the floor strength massively anyway and in effect move the notch down towards the centre of the joist.