Floating slabs are concrete slabs that are laying over the ground, without any kind of anchoring, as if it simply sits on it and floats. Floating slab, as the name tells it resembles a plate that is simply laid over water, with no kind of connection between them.

The main application of floating slabs is to use as a base foundation for sheds, manufacturing workshops, home additional room, or garages. It is economical when used in areas wherever the need for standard foundations is not required. The construction details are explained in detail in the following sections.

When we assume a building with floating arrangement, we must picturize as a building with a standard foundation of strip footing, that is constructed several feet below the ground. Then we have the wall built up above the ground surface. Then literally the floating slabs float on the ground. Here the need for ground preparation is reduced to a larger extent.

The floating slabs are called as monolithic slabs as they have no connection with the foundation. If it’s the case, only after curing of the foundation we cast the floating slab.

Construction of Floating Slab

The construction of floating slabs requires details to start the proposed building requires a solid foundation to completely support the whole weight of superstructure.

As mentioned they are more used in garages, an extension of the house or sheds that does not necessarily require huge foundations. These buildings are light in structure. So floating slabs are found most suitable and economical, compared with conventional slab construction.

The main construction layers in the floating slab are shown in figure-1. The construction involves the following steps:

Floating Slab Layers

Fig.1: Floating Slab Layers

A: Site Excavation for Floating Slab Construction

The initial stage of floating slab construction is to clear the land and excavate the area as per the plan. This is the initial preparation for the construction.

Preparation of Land for Floating Slab Construction

Fig.2: Preparation of land by removing the upper layer

The step also involves making a drainage in the sides, for the water to drain out through the gravel base as shown below. The trench constructed is sealed with geotextile and gravels as shown below, which will remove water from concrete slab foundation as shown in figure 3.

Excavated drainage and the prepared drainage

Fig.3: Excavated drainage and the prepared drainage

B: Laying Gravel Base for Drainage

Laying Gravel base layer over the area for drainage of unwanted water

Fig.4: Laying Gravel base layer over the area for drainage of unwanted water

C: Reinforcement for Slabs

The slab mold is placed for casting procedure. To strengthen the slab, the reinforcing bars are provided as per dimensions and codes.

Reinforcement in Floating Slab

Fig. 5: Reinforcement Bars Arranged in slabs

D: Casted Floating Slab

The concrete is poured into the slab formwork. It is compacted either my labor or mechanical vibrator depending on the area and workmanship. Proper compaction has to be undergone, to make the slab fully productive. Proper curing has to undergone for almost 2 to 3 days.

Concreting of Floating Slabs

Fig.6: Compaction of Poured Concrete

Advantages of Floating Slabs

  • The floating slab construction can be employed in site areas with lower load carrying capacity and where investing large money on soil treatment is futile. This system let us to use over loose soil or in the soil with varying compressibility.
  • Floating slab have the property of spreading the vertical loads or stresses coming over it to be distributed over a larger area.
  • Floating slab foundations are a good solution when comes to extension of houses. There is situation when we require a building extension without affecting the already existing foundation. This won’t interfere with the building structures already built.
  • Floating slabs behave as a barrier for the entrance of the moisture coming from the ground. It acts a barrier between the superstructure and the ground. This avoids seepage of water and frosting. For this purpose, the slab can be insulated for frost or moisture. This had made their widespread usage in cold region construction.
  • The floating slabs do not require usage of footer trenches. They can be poured with the help of trenching or digging which is economical.
  • The floating slab does not cause any disturbance to the earth layer lying beneath neither it will interfere with the quality.
  • In areas where there are possibilities of shifting in the earth layer, mainly due to high moisture content, the floating slabs are best suited.

Disadvantages of Floating Slabs

  • The floating slab does not make underground land available for underground access for connection lines facing the utilities.
  • It has a primitive technology
  • Floating slab foundation have lower design resonance