I wish to lower my kitchen ceiling. In doing so, I want the new ceiling joists to run at right angles to the existing joists. I propose to insert joist hangers into the walls on either side of the room and insert the new joists into these. The span of the new joists is 3 metres. What thickness of timber should I use ? I was thinking 50 x 100 at the most, possibly even 50 x 75 if I used some noggins at points along the span. Anyone see any problems with this ?