Waterproofing of flat terraces is a tricky problem in building construction, mainly because the surfaces are flat. This means that the water cannot run off the structure quickly, and will move slowly or pool above the surface, creating opportunities for leakage.It follows that rough terrace surfaces (such as crazy china paving) are not good for waterproofing, as they encourage slow movement or pooling of water. Smooth surfaces are better. The more slope you can give to the surface, the better. A slope of 1 in 100 or steeper is recommended for terraces.
Leakage and seepage can be caused by improper slopes, clogged drainage pipes, cracks and damages on the terrace slab, resulting in standing water on the roof which leads to seepage and leakage on the floor below.