hi some internal walls in my house was built using 50mm light weight type of block. i also have a shed attached to house which is a single skin thick. is it possible to make it into a cavity wall by leaving a 50mm gap and cutting a 100mm celcon block in half leaving it 50mm thick to do the inner skin to cut down on space. probally a mad suggestion. if this isnt much good then i will have to build a partition instead. any ideals as i dont want to dry line and space is everything. i was thinking about leaving a 50mm gap then using 50mm x 50mm to build a partition and fix a thin layer of ply to the cavity side. then completely filling in between the partition with celotex. then foil back plasterboard. any ideals between the 2 ideals.