In the process of managing a double storey extension on my home. We have a flat roof at the back which has a rubber roof covering. The 1st floor is constructed of plasmor Fibolite blocks on the outer leaf and thermalites in the inner. After prolonged rain, I get a leak coming through the flat roof, around the area where the ground and first floors meet. Is the reason for this leak down to the fact the outer blocks are getting so wet, they can’t take on any more water and causing the leak best course of action would be to get the blocks covered in clad/render?