1. Introduction
In all types of building construction; several levels ( like lintel level, sill level, etc) are provided to make the structure sound and stable. One such important level in building construction is the Plinth level.
The plinth level can be understood as the level that lies between the natural ground level and the finished floor level of the building.
The natural ground level refers to the uppermost layer of the soil present around the structure that has been duly leveled before the commencement of the construction whereas the finished floor level of the building refers to the ground floor level inside the building.
Thus, the plinth level is the component of the superstructure that is provided between the aforementioned two layers.
In other words, the plinth level can be defined as the level at which the superstructure begins and the substructure ends.
The primary objective of providing the plinth level is to prevent the ingress of moisture, dampness, and seepage of rainwater and stormwater inside the building.
The plinth height refers to the height of the plinth level from the natural ground level. Mostly, the plinth height of 300mm to 450mm is adopted from the natural ground level.
On the other hand, a minimum plinth height of 150mm is adopted from the road level. Such plinth height is provided to prevent the ingress of moisture and dampness into the superstructure.
As an additional protection to dampness, a damp proof course (DPC) is provided on the upper part of the plinth level. The DPC thus checks the entry and passage of moisture through the floors and walls.
{ Note:
Natural Ground Level: Level of the ground is termed as natural ground level.
Finished Floor Level: The ground level inside the building is finished floor level }
2. Functions of Plinth Level
The major functions of the plinth level can be listed as follows:
a. It protects the structural elements as well as the building as a whole from the seepage of moisture.
b. It acts as a medium to transfer the load coming from the superstructure to the foundation underneath.
c. It increases the aesthetic appearance of the building.
d. It also serves as a retaining wall and retains backfill soil.
e. It reduces the risk of differential settlement of the foundation.
3. Difference between Plinth and Sill Level
| Plinth Level | Sill Level |
| It is the part of the superstructure that lies between the natural ground level and the finished floor level. | It is the part of the superstructure that lies between the lower base part of the window and the finished floor level. |
| A beam is usually constructed at the plinth level. Such a beam is known as the tie beam.
| A mortar bed or cement concrete bed is usually laid at the sill level. |
| The height of plinth is generally kept between 300mm to 450mm above the natural ground level. | The height of the sill is kept based on the type of room. Generally, for the bedrooms sill height of at least 600 mm is adopted ( 2.5 ‘ is generally kept). For bathrooms; minimum 1100 mm is adopted. |
4. Difference between Plinth and Lintel Level
| Plinth Level | Lintel Level |
| It is the part of the superstructure that lies between the natural ground level and the finished floor level. | It can be defined as the part/component of the superstructure that lies between the top slab and the uppermost portion of the window or door. |
| It is primarily provided to check the seepage of dampness in the building. | It is primarily provided to transfer the incoming upward load to the adjacent or surrounding wall. |
| The height of the plinth is generally kept between 300mm to 450mm above the natural ground level. | The lintel height mostly adopted for the residential building is 7’ (2130 mm) and 7’6” (2316 mm )for the commercial buildings. |
5. Selection of Ideal Height of Plinth Level in Residential Buildings
The selection of the ideal plinth height for a particular building depends upon various factors such as existing abutting roads, type of construction, economics, etc.
It must be ensured at all times that the plinth level is above the adjacent road level or service road level to check the entry of rainwater in the building particularly during the rainy season of the year.
If the plinth height is kept too high above the abutting road level, the level of the adjoining parking area will also subsequently increase thereby posing significant difficulty for driving from the road.
The plinth height ranging from 150 mm to 600mm above the adjoining permanent road is regarded as the ideal plinth height of the building.
Generally, 3-4 stairs are required to reach the plinth level.
6. Plinth Level Protection
Plinth level protection is necessary to reduce the infiltration of water and runoff into the surrounding soil that reaches up to the plinth and can subsequently reach the floor level utilizing the capillary action.
Such type of plinth protection is ensured by pouring about 75mm to 100mm of cement concrete around the edge of the building.
Plinth protection is also done by laying plain precast slabs up to 600mm.
This ensures the prevention of water entry from around the edges of the building thereby maintaining the serviceability of the plinth level for a considerable period.
The plinth protection is mostly covered with a layer of paver blocks, stones, or gravels in the case of the well-finished buildings.
{ Note: There is a difference between plinth and plinth level. The point or level where the plinth is provided is the plinth level. Whereas, The RCC (or steel or timber) member provided at the plinth level is called the plinth. But we take plinth and plinth level as unite. So, functions and objectives are taken the same. }
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