I am in the process of extending kitchen into garage and was unsure of the best way to raise the floor level of garage up to suit kitchen.concrete slab in garage and in kitchen about 170mm difference. Had different ideas from a builder friend and 2 BCO's who have visited. Ideas include a floating floor built up in polystyrene and rigid insulation then chipboard then finish, also rigid insulation then 75mm screed then finish.The first BCO suggested a timber frame with insulation between joists. Well and truly confused anyone got a suggestion