Types of Loads on a Building: Dead, Live, Wind and Earthquake (IS 875, IS 1893)
Every structure is designed for the loads it will carry during its life. In India these are given by IS 875 (dead, imposed, wind, snow and special loads) and IS 1893 (earthquake). This article explains each type with the values most used in practice and in AE/JE exams.
1. Dead load (IS 875 Part 1)
Dead load is the permanent weight of the structure itself and everything fixed to it: slabs, beams, columns, walls, floor finishes, plaster and fixed partitions. It is worked out from dimensions and unit weights.
| Material | Unit weight (approx.) |
|---|---|
| Reinforced cement concrete | 25 kN/m³ |
| Plain cement concrete | 24 kN/m³ |
| Brick masonry | about 19–20 kN/m³ |
| Steel | 78.5 kN/m³ |
2. Imposed (live) load (IS 875 Part 2)
Imposed load is the movable load from people, furniture, stored goods and equipment. It is given as a uniformly distributed load on floor area.
| Occupancy | Imposed load |
|---|---|
| Residential rooms, kitchens, toilets | 2.0 kN/m² |
| Staircases, corridors, balconies (residential) | 3.0 kN/m² |
| Classrooms | 3.0 kN/m² |
| Flat roof with access | 1.5 kN/m² |
| Flat roof without access | 0.75 kN/m² |
3. Wind load (IS 875 Part 3:2015)
Wind pressure grows with height and with the basic wind speed of the city.
- Design wind speed: Vz = Vb × k1 × k2 × k3 × k4 (risk, terrain-height, topography and importance factors).
- Wind pressure: pz = 0.6 Vz² (N/m², with Vz in m/s).
- Design pressure: pd = Kd Ka Kc pz, but not less than 0.7 pz.
For example, with Vz = 47 m/s, pz = 0.6 × 47² = 1325 N/m², or about 1.33 kN/m². Wind usually governs tall buildings, light steel roofs and water tanks more than low RCC houses.
4. Earthquake load (IS 1893 Part 1:2016)
The horizontal seismic force at the base is the design base shear:
Vb = Ah × W, with Ah = (Z/2) × (I/R) × (Sa/g)
| Seismic zone | Zone factor Z |
|---|---|
| II | 0.10 |
| III | 0.16 |
| IV | 0.24 |
| V | 0.36 |
I is the importance factor (1.0 for ordinary buildings, up to 1.5 for critical ones like hospitals), R is the response reduction factor (3 for an ordinary moment-resisting frame, 5 for a special ductile frame), and W is the seismic weight (dead load plus a part of the imposed load).
5. Snow and special loads
Snow load (IS 875 Part 4) matters only in snowfall areas. Special loads (Part 5) include temperature effects, settlement, impact and the load combinations themselves.
Load combinations for limit state design (IS 456 Table 18)
| Combination | Factors |
|---|---|
| Dead + imposed | 1.5 (DL + IL) |
| Dead + imposed + wind or earthquake | 1.2 (DL + IL ± WL/EL) |
| Dead + wind or earthquake | 1.5 (DL ± WL/EL) |
| Uplift / overturning check | 0.9 DL ± 1.5 WL/EL |
Worked example — load on a roof slab
A 150 mm RCC slab with 1.0 kN/m² floor finish and 2.0 kN/m² imposed load:
- Self-weight = 0.15 × 25 = 3.75 kN/m²
- Total service load = 3.75 + 1.0 + 2.0 = 6.75 kN/m²
- Factored load = 1.5 × 6.75 = 10.13 kN/m²
Exam tip: In earthquake combinations the imposed load in the seismic weight W is reduced (25% when it is up to 3 kN/m², 50% above that, as per IS 1893), but in the 1.5(DL + IL) combination the full imposed load is used.
Frequently asked questions
What is the live load for a residential building?
IS 875 (Part 2) gives 2.0 kN/m² for rooms, kitchens and toilets in dwellings, and 3.0 kN/m² for staircases, corridors and balconies.
What is the live load on a roof?
For a flat roof with access it is 1.5 kN/m²; for a flat roof without access (other than for maintenance) it is 0.75 kN/m².
Which code gives earthquake loads?
IS 1893 (Part 1):2016. The base shear is Vb = Ah × W, where Ah = (Z/2)(I/R)(Sa/g).
What are the load factors in limit state design?
IS 456 Table 18: 1.5(DL + IL), 1.2(DL + IL ± EL or WL), and 1.5(DL ± EL or WL), with 0.9DL ± 1.5EL checked for uplift and overturning.
See these loads at work: the free Building Frame Designer analyses a whole house for dead, live, earthquake and wind loads in your browser.
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