Everything You Should Know About Raft Foundation In Building Construction 

Raft foundation is a popular type of foundation. Raft foundation is also called “Mat Foundation.” It’s a unique type of foundation that is done during the building process. 

To help you better have a knowledge of what raft foundation is and everything it involves, we have broken down all the different information about raft foundation you should have. 

Keep scrolling below to learn more about what a raft foundation is, what it does, and when you should use a raft foundation during building construction. 

What Is Raft Foundation? What You Should Know About It

Raft foundation is a foundation style that is made with the use of thick concrete slab sitting on a wide area of soil and is reinforced with iron steel to enable it support columns or walls while transferring loads from the building to the earth. 

What Does Raft Foundation Do?: What You Should Know

Raft foundations are commonly done in building construction for the purpose of supporting structures such as residential or commercial buildings in poor soil conditions, storage tanks, silos and large industrial equipment foundations. 

A Look At The Working Principles Of Raft Foundations

The first step is understanding how raft foundation works as it’ll enable you to understand when to make use of this during your building process. Now, let’s look into the basics of how raft foundation operates. 

During the raft foundation process, here are the things that go on:

  1. The complete load from the building is transmitted to the full ground floor area through a raft foundation. 
  2. The stress on the soul is then determined by dividing the entire weight of the structure and the self-weight of the mat by the total area of the foundation it is covering.
  3. Because the contact area of a raft foundation with the soul is significantly greater than that of any other form of foundation, the load is dispersed over a border area, which results in lesser stress on the soul and a lower risk of shear failure.

When You Should Use Raft Or Mat Foundation 

Raft foundation is one of the types of foundation design you’ll be presented with during the foundation stage of your building. However, it is mainly advisable that you use a raft foundation when the earth has a limited bearing capability. 

Here are other times you should choose raft foundation for your building process:

  • When half of the entire ground surface beneath the structure for the foundation is covered roughly. 
  • When the individual footings are overlapping because the columns or walls are positioned too closely.
  • When there’s the need to decrease soil stress.
  • When you are setting up the basement area of your building project. 

The Different Types Of Raft Foundation

There are different types of raft foundation methods you can opt for during the building process. All of them serve their individual purposes. They include:

  • Plate Mat (Flat)

This is the most basic type of raft foundation. This type of raft foundation is used when the columns and walls are regularly placed at small intervals and the applied loads are relatively minor.

During this process, more reinforcement is necessary at the column sites and load-bearing walls, and reinforcement is put in both directions. If you are on a budget, the thickness of this type of raft foundation is usually limited at 300mm.

  • Thickened Plate Under Columns 

This is used when the columns and load-bearing walls are subjected to higher loads, the slab is thickened beneath them, and more reinforcements are added to prevent diagonal shear and negative reinforcement.

Other types of unique raft foundation process include:

  • Beam & Slab in two directions
  • Plates with Pedestals 
  • A piled/up raft
  • Cellular Raft Foundation/Rigid Frame Mat

Building Materials Used For Raft Foundation

Below are the list of materials that are primarily used to construct a raft foundation. They include:

  • Formwork 
  • Iron Rod (Reinforcements)
  • Concrete 
  • Spacer


Raft foundation is a popular type of foundation system and it is due to its ease in installation and how essential it is in the building process especially when the site soil is of poor condition.

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