The wall plates(mudsills) were also rotten and had to be cut back and removed. Using a roll of dpc(damp proof course). Place the desired length on the block beam supports before placing the new wall plates, cut to required size. The wall plates may require a couple of express anchors to fix them in place. Now mark your layout for new floor joists at 400mm centres, from your first joist. Cut joists to length, place on layout and fix with a couple of 90mm toenails to wallplate.