The importance of plinth foundation
How does one explain what is ‘plinth’? My comical statement if a new client enquiries is “the foundation above ground”! Of course, no technical person would accept this definition, while the construction teams at Bangalore sites call it a basement wall. Actually, plinth is the part of a building above ground up to the ground floor.
If we walk around a typical village, many houses could be found without any noticeable plinth. Raised floor levels seem associated with the rich and important people. As such, the common image we get is that of a landlord sitting high on verandah platform and ordering his labourers! However, it is important to realise that plinth is also an ecological necessity, even though it costs dearly!
The elderly in the community may say that a high plinth avoids crawling creatures from entering the building, if there are open areas around with snakes, lizards and such others. From construction experiences, there are deeper reasons. Surface water tends to flow all over the top soil, especially during the monsoon, before it percolates at the softer parts. If it flows at sub-floor levels, under the building, it can lead to part of the structure sinking and walls cracking, termed as unequal settlements. Plinth provides stability to the building and the consolidated earth filling inside the plinth provide a stable sub-floor for the floor finish.
Other important roles
Among the more important roles of plinth is ensuring adequate height for the toilets and bath-water traps, ensuring their smooth gravity flow into the sewage systems or drains. By misfortune, if the roadside chambers get clogged, houses with high plinth do not face back flow of sewage into the toilets.
The subsoil water tends to flow up the building walls, which needs to be stopped before the superstructure begins. Accordingly, a layer of concrete called damp-proof course or traditionally a stone slab is laid just before the wall starts. This course, in short called DPC, laid on top of the plinth, distances the floor from the ground water. Incidentally, it also acts as a levelling course for the wall such that all of the first row bricks are at same level.
One final clarification: how high should the plinth be? There is no fixed answer, but keep it at least 1′ 6” above natural ground. In waterlogged areas, the higher the better. After all, it adds to the safety of a house.