I was asking a few days ago about fixing batons to a concrete slab so I could have t&g floor inplaceof the screed floor. I now have to rethink my approach as the living room extenstion built some time before 1975 must have been built by a cowboy. I started to break up the screed and found it as about half an inch thick laid onto a load of old rubble, bricks bits of blocks and sand and ballast. This was about 6 inchs thick and underneath is some very rough concrete it looks just like old infill. There is no sign of any dpc. Now if I continue to dig all of this rubbish out and lay proper loists what size timber should I use. The joists in the rest of the house are 4x2. They are supported mid way across their span by a small retaining wall. The extension is 9ft 4ins wide, if I use 4x2 joists will they span the extension without support or should I consider a deeper joist.
Kevin