Floating Slab Foundations: Exploring the Benefits

What Is a Floating Slab?

A floating slab, also known as a float slab foundation, is a type of concrete foundation that is constructed by pouring a reinforced concrete slab directly over the soil. Unlike traditional concrete foundations, which are anchored to footings that are dug deep into the ground, floating slabs are designed to “float” on top of the soil.

This makes them a popular choice for construction projects on sites with poor soil conditions or high water tables, where conventional foundations may be difficult or expensive to install. Floating slabs can also be used as a base for outdoor structures such as sheds, garages, and patios. They are relatively quick and easy to install and can be customized to suit a wide range of building requirements.

Why Use a Floating Slab?

Floating Slab
Floating Slab Foundations: Exploring the Benefits 6

Using a floating slab foundation is considered one of the most cost-effective methods of building a foundation of a house. Normally, a strip foundation is used for house foundation construction using a frosted wall above.

Strip footings are construction lower than the frost level of the area and which is typically kept between 3 ft to 4 ft below grade level. The construction cost of strip footing and front wall construction is generally higher compared to normal foundation construction which involves a larger area to be excavated for a foundation with more concrete work and labor work required.

Read More: Floating Slab Vs Monolithic Slab | What Is Monolithic Slab | What Is Floating Slab

floating slab vs monolithic slab

A floating slab and a monolithic slab are two different types of concrete foundations used in construction. While both types of slabs are made of concrete, there are some key differences between them.

A floating slab is a concrete slab that is poured directly onto the ground, without a traditional foundation. It is typically used in situations where the ground is unstable or there is a high water table. A floating slab is not anchored to the ground, but instead “floats” on top of it, which can help prevent cracking and settling.

On the other hand, a monolithic slab is a type of foundation that combines the slab and the footing into a single, continuous pour of concrete. The slab and the footing are poured at the same time, and the footing is designed to be thicker and wider than the slab to provide additional support.

In terms of cost, a floating slab is generally less expensive than a monolithic slab because it requires less material and labor. However, a monolithic slab may be more suitable for certain types of structures, such as larger buildings or structures in areas with high wind loads or seismic activity.

Construction of Floating Slab

Construction of Floating Slabs requires details. The proposed building requires a solid and strong foundation to fully support the entire superstructure’s weight on it. As mentioned they are more commonly used in garages, and extensions to a house or shed do not necessarily require a large foundation. These buildings have less structural load compared to others.

Hence Floating Slabs are found to be most suitable and economical as compared to conventional slab construction. The main construction layers in a floating slab are shown in Figure-1. The construction includes the following steps:

1. Site Excavation for Floating Slab Construction

Site Excavation For Floating Slab
Floating Slab Foundations: Exploring the Benefits 7

The first step to being done in floating foundation construction is to clean the land and excavate the area as per the plan. This is the preliminary preparation for construction.

The step also includes creating drainage in the sides to drain water through the gravel base as shown below. The constructed trench is sealed with geotextiles and gravel as shown below, which will drain water from the concrete slab foundation.

2. Laying Gravel Base for Drainage

Install a gravel grid before pouring gravel. Add an 8- to 12-inch gravel base of various rock sizes, compacting each layer for durability.

3. Reinforcement for Slabs

Reinforcement Of Floating Slab
Floating Slab Foundations: Exploring the Benefits 8

A slab mold is placed for the casting process. For reinforcing slabs, reinforcing bars are provided as per the dimensions and code.

4. Casted Floating Slab

Concrete is poured into the slab formwork. This compresses either my labor or a mechanical vibrator, depending on the area and workmanship. Proper compaction has to be done to make the slab fully productive. Appropriate treatment has to be taken for about 2 to 3 days.

Read More: What Is Floating Foundation | Suitability of the Floating Foundation

How to Build a Floating Slab?

Floating Slab Components
Floating Slab Foundations: Exploring the Benefits 9

Step: 1 Prepare A Ground Floor Slab

Firstly, Drive the four stakes at each corner of the floating slab. You also use line, level, or builder’s level to check the slope of the ground at the construction site.

If there is an excessive slope at the site and flattening it means moving tons of soil which will increase construction costs.

So, try to cut down the higher side and fill the soil on the lower side of the slab. It will reduce the cost of moving soil from the side as it settles down in the same place.

Step: 2 Mark and Lever On Side

Prepare a wooden board form of size 2×12 length or join it with a cleat to mark one face of concrete forms and fix it with corner stakes.

Again level 2×12 wooden board and fix it with the second corner of the slab. 2×12 boards are best suited for constructing 5 in tick slabs for garages and sheds.

Step: 3 Do Bracing of Stakes and Side Forms

Fix the Manson line on the top of the 2×12 wooden board. Align this 2×12 board to match the string and brach it or fix it with 2×4 spaced pairs which are placed every two feet apart.

Forms are braced to ensure the sides remain straight in position during the pouring of concrete. Because fresh concrete can push these board outside which result in a curve shape of the slab on the sides of the flooring slab.

Step: 4 Fix the Other Side with the Stake and Level it

Prepare a second 2×12 wooden board with a size equal to the width of the slab. Fix one side end with braced form and set it at 90 degrees using diagonal length calculation. Drive stake fixers at the end and level it and brace 2nd wooden board form.

Similarly, add the 3rd and 4th sides of the floating slab formwork.

Step: 5 Level and Fill Work

Now, Fill 3 inches of granular soil keeping five inches margin from the top of the forms. Level and tamp this fill properly.

After filling we must have to check that the 5-inch margin is left out in the whole slab area. For that stretch, the string between the top of the two forms at the various positions and check the distance.

Step: 6 Compact the Fill

Properly compact the soil with a plate compactor. Left 12×12 In deep and wide trench around edges of slab to thickness the edges of the slab.

Step: 7 Insert Steel Rebars to Increase Slab Strength

Now, Spread a 5 mm thick plastic sheet to cover the entire area of the slab. Fix two steel bars of 1/2 inch dia to the stake keeping at least 4 inches distance from a wooden board from work.

Step: 8 Prepare Slab Partition

Spread the grid of steel bars on a plastic sheet each at least 4 feet spaced from the other. Divide the entire slab into various parts with the use of 2×4 wooden boards.

Keep this board aligned with string stretched between the top edges of 2×12 wooden planks.

Step: 9 Calculate the Volume of the Concrete

Calculate the volume of concrete needed to pour the floating slab by multiplying its length, width, and depth together. This will give the volume of concrete in cubic feet.

Now, divide the concrete volume by 27 to get a cubic yard of concrete. Place your order of Ready Mix Concrete at least one day before slab casting.

Step: 10 Pour Concrete and Properly Level it

Use a Wooden screed board to level the concrete and give it a smooth finish. Take a number of passes over the concrete surface to finish it well.

Step: 11 Make Round Concrete Edges

Rounding off concrete slab edges can be done with an edging tool. Remember, perform this work after surface water from concrete is disappeared from it.

Step: 12 Insert Achor Bolts

Insert 1/2 inch dia anchor bolts at every 6 feet distance apart. Keep about 2.5 inches of the bolt above the concrete surface.

Step: 13 Prepare Expansion Joints in Concrete

Make expansion joints in concrete to avoid random track by using groover tools.

Step: 14 Do Proper Curing and Let It Harden

Do proper curing of concrete with water at least for 24 houses and let it gain sufficient strength. You can also use a curing compound to make the curing process fast.

Step: 15 Remove Forms Properly

Remove concrete forms properly without damaging the slab. Repair any cavity left out in concrete with rich cement mortar mix.

Advantages of Floating Slabs

Floating Slabs have the following advantages,

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Floating Slab Foundations: Exploring the Benefits 10
  • The major advantage of using floating slabs is that they can be constructed on low-bearing capacity soil. Also, where there is money investment for soil treatment to increase soil bearing capacity is too expensive.
  • These slabs have the property of spreading the vertical load or the stress on it to be distributed over a large area.
  • The floating slab is best suited when there is a need for an extension of the house area. It is very easy and cost-effective in the case of a floating slab foundation to extend the house without disturbing the existing structure of the house foundation.
  • The floating slab foundation does essential need to have a footer excavation trench. This slab can be filled with concrete only by digging and teaching in the foundation.
  • The floating slabs act as a barrier to the entry of moisture coming from the ground. It acts as a barrier between the superstructure and the ground.
  • It protects against water seepage and frost. For this purpose, the slab can be insulated from frost or moisture. This led to their widespread use in cold-field construction.
  • The layer of soil lying below the floating slab does not disturb nor will it interfere with the quality.
  • In cases, where there are changes in soil layer settlement due to heavy moisture content in the soil, the floating foundation provides the best solution.

Disadvantages of Floating Slabs

Along with advantages Floating Slab also has some disadvantages as listed below,

  • The floating slab does not provide
  • underground access for the connection lines facing the utilities.
  • It’s primitive technology.
  • Floating slab foundations have low design resonance.

Read More: Monolithic Definition | Monolithic Slab | Monolithic Footing | Monolithic Foundation | Advantages & Disadvantages of Monolithic Slab Foundation

Uses of Floating Slab

A floating Slab can be used for the following conditions,

  • The primary use of floating slabs is as a base for
  • industrial workshops, sheds, and garages.
  • It is very cost-effective in areas where need foundation is not required.


What Is a Floating Slab?

A floating slab is a type of concrete foundation that is poured directly onto the soil, without a traditional foundation. It “floats” on top of the soil, which can help prevent cracking and settling.

What are the benefits of using a floating slab?

The benefits of using a floating slab include cost-effectiveness, flexibility, ease of installation, and suitability for poor soil conditions or high water tables.

What types of structures are suitable for a floating slab?

Floating slabs can be used for a wide range of structures, including residential and commercial buildings, industrial buildings and warehouses, and outdoor structures such as sheds, garages, and patios.

What is the construction process for a floating slab?

The construction process for a floating slab typically involves preparing the site, pouring and leveling the concrete, installing reinforcing steel, and curing and finishing the slab.

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1 thought on “Floating Slab Foundations: Exploring the Benefits”

  1. Nice Article, Well described Floating Slabs, Basically, I saw using these Floating slabs in a variety of structures, garages, cottages, and sheds.

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