I want to convert the loft of a terraced house into a bedroom. I measured the size of current beams and they are 6” x 2 ½” . What is the recommended size for a loft conversion? I also noticed that the loft seams to already have some frame work in there and it seems that at some stage plaster boards where nailed to it (the nails are still in there) there is also a door frame on one side.