Hi I'm planning to raise my loft floor by 150mm to accommodate more insulation under it. The existing joists are 100x47 and I'm going to put 150x47 on top of them. Is there a "correct" way of doing this? i.e. can the new joists just be placed on top of the existing ones (i.e. in line with them) with some bracing between them for lateral stability, or should they be installed perpendicular to the existing joists? Does it make any difference to the roof structure?