One client decided that he wanted to add depth to his basement. He decided to break his concrete slab and lower it. Unfortunately, when he remade his concrete slab, he put it back next to the foundation footing without putting a draining membrane on the foundation walls or a French drain under a slab. The age of the building being quite old, the waterproofing of the foundations is obsolete. At the first rain the water entered its new slab. He would have had to install drainage and waterproof his foundation.