Shallow foundations are the most commonly used foundation type for residential and light commercial buildings because they are cost-effective, easy to construct, and suitable for stable soil conditions.
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| Type of Shallow Foundations |
In this post, we’ll explore the different types of shallow foundations, their applications, advantages, disadvantages, and key considerations for choosing the right one. By the end, you’ll have a clear understanding of which foundation type best fits your project—whether you're building a house, a small office, or a warehouse.
What Are Shallow Foundations?
A shallow foundation is a type of foundation that transfers building loads to the earth very near to the surface, rather than to a subsurface layer or a range of depths as with deep foundations. Generally, the depth of a shallow foundation is less than its width. These are economical and relatively easy to construct.
Shallow foundations, also called spread footings, transfer structural loads to the soil near the surface (typically at a depth less than the footing’s width). They are ideal when:
✅ The soil has good bearing capacity.
✅ The building loads are relatively light (e.g., homes, small commercial buildings).
✅ Deep foundations (like piles or caissons) are unnecessary and too expensive.
When Are Shallow Foundations Used?
✔ Residential homes (single-story or two-story buildings).
✔ Small commercial buildings (offices, shops, warehouses).
✔ Boundary walls & retaining walls.
✔ Structures on firm, stable soil.
Now, let’s dive into the 7 main types of shallow foundations as shown below:
1. Isolated (Spread) Footings
What Are They?
Isolated footings, also known as Spread Footings are individual concrete blocks placed under single columns or pillars. The load from the column is spread out evenly over a wider base so that the soil can safely bear the pressure.
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| Isolated Footing |
It's Best For:
✔ Single-column structures (e.g., sheds, pergolas).
✔ Framed structures with spaced columns.
Characteristics:
✔ Square, rectangular, or circular in shape.
✔ Economical for light to moderate loads.
✔ Made from reinforced concrete.
Where Do You See Them?
✔ Residential homes
✔ Small commercial buildings
✔ Structures with widely spaced columns.
Advantages:
✔ Cost-effective for small projects.
✔ Simple construction (no heavy machinery needed).
✔ Works well on firm soil.
Disadvantages:
❌ Not suitable for weak or expansive soils.
❌ Requires precise alignment to prevent uneven settlement.
2. Combined Footings
What Are They?
Combined footings support two or more columns when they are too close for separate footings. They can be rectangular or trapezoidal.
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| Combined Footing |
✔ Adjacent columns with overlapping footings.
✔ Eccentric loading (e.g., a column near a property line).
Characteristics:
✔ Supports more than one column.
✔ Shape depends on load and column positioning.
✔ Reinforced with steel bars for added strength.
Where Do We See Them?
✔ Columns placed near property boundaries
✔ Situations where space constraints exist.
Advantages:
✔ Efficient use of materials
✔ Reduces differential settlement.
✔ More space-efficient than isolated footings.
✔ Economical for clustered columns.
Disadvantages:
❌ More complex design required.
❌ Needs accurate load distribution calculations.
3. Strip Footings (Wall Footings)
What Are They?
Strip footings are continuous concrete strips that run under load-bearing walls, distributing weight evenly. It distributes the load of the wall over a wider area.
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| Strip Footing |
✔ Residential homes with masonry walls.
✔ Boundary walls & retaining walls.
Characteristics:
✔ Long and narrow
✔ Used under walls
✔ Can be plain or reinforced concrete.
Where DO We See Them?
✔ Load-bearing walls in residential buildings
✔ Partition walls
✔ Light industrial buildings.
Advantages:
✔ Simple & economical for long walls.
✔ Provides uniform support.
Disadvantages:
❌ Not ideal for heavy point loads.
❌ Can suffer differential settlement if soil varies.
4. Raft (Mat) Foundations
What Are They?
A raft foundation is a large concrete slab covering the entire building area, spreading the load uniformly.
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| Raft Foundation |
It's Best For:
✔ Weak or compressible soils.
✔ High-rise buildings with heavy loads.
✔ Basements & underground structures.
Characteristics:
✔ Thick slab covering the entire footprint of the structure
✔ Reinforced heavily with steel
✔ Designed for poor soil conditions or heavy loads.
Where Do We See Them?
✔ High-rise buildings
✔ Buildings on weak or expansive soils.
✔ Industrial structures.
Advantages:
✔ Minimizes settlement in poor soil.
✔ Great for large, heavy structures.
Disadvantages:
❌ Expensive (high concrete & steel usage).
❌ Requires deep excavation.
5. Strap (Cantilever) Footings
What Are They?
Strap footings connect two isolated footings with a rigid beam to balance uneven loads.
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| Strap Footing |
It's Best For:
✔ Columns near property lines.
✔ Eccentric loading conditions.
Advantages:
✔ Prevents tilting of adjacent footings.
✔ Balances load distribution.
Disadvantages:
❌ Complex design & construction.
❌ Needs precise engineering.
6. Grillage Footings
What Are They?
Grillage footings use layered steel or timber beams encased in concrete to spread heavy loads.
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| Grillage Footing |
It's Best For:
✔ Heavy industrial columns.
✔ Transmission towers & bridges.
Characteristics:
✔ Constructed with steel I-beams
✔ Embedded in concrete for protection
✔ Layered arrangement for load transfer.
Where Do We See Them?
✔ Heavy industrial structures
✔ Columns supporting large machinery
✔ Temporary structures.
Advantages:
✔ Handles heavy concentrated loads.
✔ Reduces excavation depth.
Disadvantages:
❌ High material & labor cost.
❌ Not for all soil types.
7. Slab-on-Grade Foundations
What Are They?
A single thick concrete slab poured directly on the ground, acting as both foundation and floor.
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| Slab on Grade Footing |
It's Best For:
✔ Residential homes in warm climates.
✔ Garages & workshops.
Characteristics:
✔ Direct contact with soil
✔ Often includes wire mesh or steel reinforcement
✔ Typically used in warmer climates.
Where Do We See Them?
✔ Garages
✔ Warehouses
✔ Residential homes without basements.
Advantages:
✔ Fast & cheap construction.
✔ No basement or crawl space needed.
Disadvantages:
❌ Vulnerable to ground movement.
❌ Hard to repair underground utilities.
Conclusions
Shallow foundations are versatile, economical, and widely used in construction. By choosing the right type whether isolated, combined, strip, raft, strap, grillage, or slab-on-grad you ensure a stable and durable structure.
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