i need to build up a floor in my new extension the size of the room is 5mx 3m itwill be a lounge. at present the floor is the concreat slab which as been inspected by building control and as dpc and insulation under it,,, the slab is approx 80mm lower than the exsisting floor which i would like to bring it on level with,, can i lay down lenths of 2x2 on sand and cement to level them and then lay 22mm chip board flooring on this? any ideas ?