When planning or designing a house, one of the most important aspects is deciding the column size. Columns carry the total load of the building and transfer it to the foundation, so choosing the right size is essential for safety and stability. The minimum column size for a 2 storey building is not just a random number it depends on load calculations, material strength, and design standards. In this guide, we will explain the minimum column size requirements, reinforcement details, practical considerations, and FAQs to help you understand this topic in detail.
What is a Column in Building Construction?
A column is a vertical structural member that transfers loads from beams and slabs down to the foundation. Without columns, multi-storey buildings cannot stand because walls alone are not strong enough to carry heavy loads. For a 2 storey building, columns ensure that the weight of the upper floor and roof is safely transferred to the ground. Columns are designed according to structural engineering principles. Their size, reinforcement, and spacing are determined based on building height, soil condition, and load distribution.
Importance of Choosing the Right Column Size
The minimum column size for 2 storey building is critical because undersized columns may lead to cracks, structural failure, or even collapse. On the other hand, unnecessarily large columns can increase construction costs and reduce usable space inside the house. The right column size ensures safety of the structure, even load distribution, longer building life, compliance with IS codes or relevant building standards, and cost efficiency.
Minimum Column Size for 2 Storey Building
The general minimum column size for a 2 storey building is 9” x 9” (225mm x 225mm) when using M20 grade concrete with Fe500 steel. However, this size is only safe for small residential houses with light loads. For stronger stability, most engineers recommend 12” x 9” (300mm x 225mm) or 12” x 12” (300mm x 300mm) columns.
Factors Affecting Column Size
The exact size depends on building load (dead load + live load), soil bearing capacity (SBC), height of building (floor-to-floor height), distance between columns (span), and type of materials used (concrete grade, steel grade).
Standard Column Sizes for 2 Storey Buildings
Here are common recommendations:
| Building Type | Minimum Column Size | Recommended Column Size |
|---|---|---|
| Small house (G+1, 2 storey, light loads) | 9” x 9” (225mm x 225mm) | 12” x 9” (300mm x 225mm) |
| Medium house (G+1 with heavier loads) | 12” x 9” (300mm x 225mm) | 12” x 12” (300mm x 300mm) |
| Large span or heavy load structures | 12” x 12” (300mm x 300mm) | 15” x 12” (375mm x 300mm) |
| From this, we can see that while 9” x 9” is technically the minimum column size for a 2 storey building, a safer and more practical choice is 12” x 9” or larger. |
Column Reinforcement for 2 Storey Buildings
Choosing the right reinforcement is as important as selecting the size. A column without proper reinforcement cannot handle bending moments or seismic forces.
Longitudinal Bars
Minimum 4 bars for rectangular or square columns, minimum 6 bars for circular columns, and recommended diameter is 12mm – 16mm (Fe500 steel).
Lateral Ties (Stirrups)
Minimum diameter 6mm – 8mm, spacing 150mm – 200mm center-to-center, placed to hold main bars in position and resist buckling.
Column Size Calculation Method
The minimum column size for 2 storey building can also be calculated using load formulas. The column load is determined from slab load + beam load + wall load + live load. Basic formula: Pu = (Dead Load + Live Load) x Load Factor. Then, the column area required is: A = Pu / (0.4 x fck), where Pu = ultimate load on column and fck = characteristic compressive strength of concrete (e.g., 20 MPa for M20). Using this method, engineers adjust the column size based on actual building loads.
Placement of Columns in 2 Storey Houses
Even if you choose the correct minimum size, poor placement can weaken the building. Columns should be placed at corners, wall junctions, and load concentration points. Spacing between columns should not exceed 4–5 meters for residential buildings. Symmetrical placement ensures proper load transfer.
Difference Between Minimum and Recommended Column Size
Minimum size is the smallest safe size (9” x 9” for 2 storey) that prevents failure under basic loads. Recommended size is a practical size (12” x 9” or 12” x 12”) that provides safety margin against earthquakes, wind loads, and future modifications. This is why engineers rarely suggest only the minimum—they prefer a slightly larger size for safety.
Common Mistakes in Column Design
When planning a 2 storey house, people often make these mistakes: using undersized columns (less than 9” x 9”), not consulting a structural engineer, using poor quality concrete or steel, placing columns unevenly, and ignoring soil test before construction.
FAQs on Minimum Column Size for 2 Storey Building
What is the minimum column size for a 2 storey building?
The minimum column size is 9” x 9” (225mm x 225mm) with M20 grade concrete and Fe500 steel.
What is the recommended column size for better safety?
Most engineers recommend 12” x 9” (300mm x 225mm) or 12” x 12” (300mm x 300mm) for better safety and durability.
How many columns are required for a 2 storey house?
The number depends on the layout and span, but generally 8–12 columns are needed for a small 2 storey residential house.
Can 9” x 9” columns be used safely?
Yes, but only for small houses with light loads. For long-term safety, larger columns are better.
Which concrete grade is best for columns?
M20 is the minimum grade as per IS codes, but M25 or higher is recommended for durability.
What happens if column size is too small?
It may lead to cracks, deflection, and in worst cases, structural collapse.
Final Thoughts
The minimum column size for 2 storey building is 9” x 9” (225mm x 225mm), but this is only suitable for very small residential houses. For most 2 storey houses, a safer option is 12” x 9” or 12” x 12”, depending on the load, soil conditions, and span. Along with proper reinforcement and placement, this ensures safety, durability, and compliance with standards. If you are building a 2 storey house, always consult a structural engineer before finalizing column size. Proper design will save you from costly mistakes and ensure the long-term strength of your building.
