IS 875 & IS 1893 — Design Loads on Buildings Explained

Before anything can be sized, the loads have to be known — and IS 875 is where they come from. It gives the dead loads, the imposed (live) loads, the wind loads, snow loads and how they combine. Earthquake loads come from a separate code, IS 1893. Together they define what every column, beam and slab in a house is actually designed to carry.

IS 875 Part 1 — Dead loads

Dead load is the permanent self-weight of the structure and everything fixed to it. Part 1 gives the unit weights used to compute it:

Material	Unit weight
Reinforced concrete (RCC)	25 kN/m³
Plain concrete (PCC)	24 kN/m³
Brick masonry	~19–20 kN/m³
Floor finish + plaster	~1–1.5 kN/m²

A 125 mm RCC slab therefore weighs about 3.1 kN/m² before finishes — the number that anchors every column load calculation.

IS 875 Part 2 — Imposed (live) loads

Live load is the movable, occupancy load. Part 2 tabulates it by use:

Space	Imposed load
Residential rooms	2 kN/m²
Balconies, staircases, corridors	3–4 kN/m²
Accessible flat roof	1.5 kN/m²
Non-accessible roof	0.75 kN/m²

The 2 kN/m² residential figure is the one behind almost every house calculation; balconies and stairs are deliberately higher because crowds gather there.

IS 875 Parts 3–5 — Wind, snow and combinations

Part 3 (wind): design wind speed by region, then pressure by height, terrain and building shape. It governs tall, slender and hill-site buildings more than ordinary low houses.
Part 4 (snow): relevant only in snow regions.
Part 5 (combinations): how dead, live, wind and seismic loads are combined, so a structure is checked against realistic worst cases rather than every load at its peak at once.

IS 1893 — Earthquake loads

IS 1893 (Criteria for Earthquake-Resistant Design of Structures) places every location in a seismic zone (II to V) and gives the method to compute the design base shear from the zone factor, the building's importance, its response and its weight. It answers the question "how hard is the ground expected to shake here?" — and it works hand in hand with IS 13920, which details the members so they can survive that shaking.

Where loads meet the ultimate limit state

For the collapse check, IS 456 multiplies these service loads by a partial safety factor — 1.5 for the usual dead-plus-live case — so the structure has a margin above the heaviest realistic load. That single 1.5 is why a "service load" and a "factored load" are different numbers on every drawing.

Frequently asked questions

What is IS 875? The Indian Standard code of practice for design loads (other than earthquake) on buildings and structures, in five parts: dead loads, imposed loads, wind loads, snow loads and load combinations.

What is the live load for a residential building as per IS 875? 2 kN/m² for residential rooms; balconies, staircases and corridors are taken higher, at 3–4 kN/m².

Which code covers earthquake loads? IS 1893 — it defines the seismic zones and the design base shear; the ductile detailing to resist it is in IS 13920.

What unit weight of RCC does IS 875 use? 25 kN/m³ for reinforced concrete and about 24 kN/m³ for plain concrete.