When building a house, most people focus on elevation design, room layout, and interior finishes. However, the true strength of any structure lies beneath the surface in its foundation. A properly designed foundation ensures structural stability, prevents settlement issues, and increases the life of the building.

One of the most practical foundation systems used in residential and commercial construction is the cantilever footing. Especially in urban areas with small or boundary-restricted plots, this type of footing becomes highly useful.

In this detailed guide, we’ll explore everything you need to know about cantilever footing from definition and working principle to design considerations, advantages, disadvantages, and construction steps.

What Is Cantilever Footing?

A cantilever footing, also known as a strap footing, is a type of combined foundation system where two isolated footings are connected by a rigid beam called a strap beam.

This beam transfers load from one column to another to balance soil pressure under the footings.

It is mainly used when:

• A column is located very close to the property boundary

• The footing cannot be extended beyond the plot line

• There is eccentric loading

• Load balancing between columns is required

In simple words, when a column is near the edge of a plot and a normal centered footing is not possible, a cantilever footing helps distribute the load properly without crossing the boundary.

Why Cantilever Footing Is Needed

In densely populated urban areas, residential plots are often small such as 20×40 ft, 25×50 ft, or 30×40 ft plots. When constructing a building on such sites, columns are sometimes positioned very close to the boundary.

In a normal isolated footing:

• The footing should extend equally on all sides of the column.

• This keeps soil pressure uniform.

However, when a column is near the boundary:

• The footing cannot extend outward beyond the property line.

• This causes eccentric loading.

• Uneven soil pressure develops.

• Settlement risk increases.

To solve this issue, engineers connect the edge footing with another interior footing using a strap beam. This connection balances the load and prevents uneven settlement.

Components of Cantilever Footing

A cantilever footing system consists of the following parts:

1. Edge Footing

This is the footing provided under the boundary column. It usually experiences eccentric loading.

2. Interior Footing

This footing is placed under an interior column. It helps balance the load transferred through the strap beam.

3. Strap Beam

The most important component. This reinforced concrete beam connects both footings and transfers bending moments between them.

4. Columns

Columns transfer structural loads (dead load + live load) to the footing.

5. Reinforcement Steel

Steel bars are provided in both footings and strap beam to resist bending and shear forces.

How Cantilever Footing Works

The cantilever footing works on the principle of load transfer and moment balancing.

Here’s how it functions:

1. The boundary column produces an eccentric load because the footing cannot extend outward.

2. The strap beam connects it to the interior footing.

3. The beam transfers part of the moment and load to the interior column.

4. Soil pressure becomes uniform under both footings.

5. Differential settlement is prevented.

The strap beam itself usually does not rest directly on soil. It is designed to remain above ground or lightly supported, so it acts structurally rather than bearing soil pressure.

Where Cantilever Footing Is Used

Cantilever footing is commonly used in:

• Residential buildings on small plots

• Row houses

• Duplex houses

• Commercial buildings with property line restrictions

• Structures constructed close to neighboring buildings

• Buildings with uneven column loads

In cities where plots are compact and every inch matters, this foundation type becomes extremely practical.

Advantages of Cantilever Footing

1. Ideal for Boundary Columns

It allows construction without violating property lines.

2. Prevents Uneven Settlement

Load balancing reduces differential settlement.

3. Structurally Efficient

Transfers bending moments effectively.

4. Economical for Restricted Sites

Avoids constructing oversized footings.

5. Suitable for Medium Soil Conditions

Works well where soil bearing capacity is moderate.

6. Maintains Structural Alignment

Ensures building remains stable and vertical.

Disadvantages of Cantilever Footing

While beneficial, it has certain limitations:

• Requires detailed structural calculations

• More complex than isolated footing

• Needs precise reinforcement placement

• Not suitable for very weak or highly compressible soil

• Construction supervision must be strict

Improper design or poor workmanship can lead to cracking or structural imbalance.

Cantilever Footing vs Combined Footing