In building construction, waterproofing a flat terrace is problematic as the surface which is entirely flat does not allow the water to run off the structure. In most cases, the water remains stagnant and pools above the surface, which in turn paves the way for leakage inside the house from the roof. Again, the flat surfaces require collection pits for the water to find a way to the vertical drainage pipes, which may still be responsible for causing leakage.
Note that a rough terrace surface like a china paving is not good for waterproofing because it assists slow movement of water, which may lead to water accumulation and leakage. Nevertheless, smooth surfaces are better for terrace waterproofing and the more slope you can provide to the surface, the better. A gradient of 1 in 100 or steeper is recommended for terraces to assist the waterproofing solution in use.
There are various waterproofing solutions for a flat terrace, but the best possible way to waterproof it is with the use of a waterproofing membrane. A thin layer of waterproofing material is continuous and hence gives no path for water to enter the structure. The membrane is installed on top of the structural slab. On top of it, a filler material is placed. The filler material provides a slope to the terrace finish. The slope runs towards the drainage outlets. The final layer is the finishing layer. Finishing can be provided by any material like tile, stone, or any material, which can protect the roof and membrane against external conditions. Note that, the finish and filler layers do not contribute to the waterproofing itself.
The critical areas in membrane waterproofing solution are the areas where the membrane is not continuous. The areas where this waterproofing solution is likely to fail are the outlets, which may entail drainage sumps where water gets collected before flowing into the drainage pipes.
In the case of membrane waterproofing as a terrace waterproofing solution, if a failure occurs, it is not easy to rectify. The reason for which is that the membrane is not accessible once the installation has been made. In case, there is any collapse, to correct the mistake, the construction workers will have to take out the filler material and floor finish, and either repair or replace the entire waterproofing membrane. Also, the upper layers have to be reapplied.