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Hello i have an issue with a renovation project. I have a house to renovate, 1.5 storey. The upstairs was, shall we say - unofficial. Building control don't care, the house is nearly 50 years old and I believe B/C only have 20 years of enforcement on a particular property. Since the house came like this, it has Grandfather rights, even though I have a Building Warrant to 'Cathedral Ceiling' half the house. The entire house is being renovated. My current issue is the First Floor Joists - these are 2"x 6". The house is double block, there is a load bearing wall running the length of the house (12.5m from internal gable to gable) and the internal width of the house is approximately 7.4m. There is an open span of approximately 3.65m on either side of the 100mm wide load bearing timber wall. The block walls, as typically of Highland Houses of the time, must have had a concrete pour done at the top of the walls to create what is essentially a ring beam. The wall including cavity width is approximately 275mm, there is a 30mm thick top plate fixed to the inner block leaf (hardwood - looks like mahogany) and the ceiling ties are fixed to that. There is a board fixed to the ceiling ties running down the length of the house and the rafters are fixed through this board into the top of ceiling ties/first floor joists (looks like it does the exact same job as a ridge board - only keeps everything in line). I have sistered half the ties with 47 x 150 (on one side of the load bearer), bolted at 600mm centres using M12 Threaded Rod and Square Washers with Nyloc Nuts. My Engineer seems happy with this, but what if I want to add deeper joists like 175 x 75? The reason I have sistered the joists right now - I will be collapsing the load bearer to fill in the underfloor void on the ground floor, adding around 80 ton of hard core, slab, rebuild load bearer then insulate and screed over underfloor heating. The span of the new timber I have kept at 4.8m to overlap the load bearer and the ceiling tie join above the load bearer and bolted it all the way to it's end. Main problem I have is deeper floor joists if fitted between existing ties - how can these be fitted to existing top plate? I can't fix hangers because between existing ties there are only voids. Picture attached for clarity. Do I fix timber between all current ties with brackets and then fit new joists to them or is it just as well to continue with the sistering of 47 x 150 to the original 50 x 150 - and what is anyone's thoughts on the sistered joists? There is going to be 1 large bedroom in the upstairs space with an ensuite shower room (abs plastic shower tray, not stone), there will be a fitted wardrobe and another cupboard. Basically, there will still be less weight on the floor than there has been for most of the last 40 odd years, there was 3 or 4 rooms in the upstairs space until I stripped the house over the last few weeks. Thank You