Imposed loads for houses in India (IS 875 Part 2)Beta

IS 875 is the Indian Standard code of practice for design loads (other than earthquake) for buildings and structures. Part 1 gives dead loads (unit weights of materials), Part 2 imposed loads, Part 3 wind, Part 4 snow and Part 5 load combinations. Earthquake loads are in IS 1893.

Part 2 Table 1 gives the uniformly distributed load (UDL) and the concentrated load for each type of floor, grouped by occupancy. Table 2 gives roof loads. Floors are designed for whichever of the UDL or the concentrated load gives the worse effect; the table below lists the UDLs.

Hotels, hostels and dormitories are rows i(c)1 to i(c)10 of the same table: 2.0 kN/m² for bedrooms, 3.0 for kitchens and corridors, 4.0 for dining rooms and balconies.

Also check column 4 of Table 2, which gives minimum total loads over a 1 m wide strip or over a member's span, and the 0.9 kN concentrated load in clause 4.2. Row ii applies to roof sheeting and purlins; members that support purlins may take two-thirds of it (clause 4.5.1). A roof used as a terrace or for assembly takes the Table 1 floor load for that use (clause 4.1.1).

Where the positions of partitions are not known, IS 875 Part 2 adds a uniformly distributed load of at least one third of the weight per metre run of the finished partitions, with a minimum of 1 kN/m². This applies to partitions weighing up to 1.5 kN/m² of wall area and up to 4.0 kN per metre of length.

Plastered brick partitions are usually heavier than that, so they are normally taken as a dead line load on the slab or beam below rather than as this allowance.

A two-storey house with 230 mm plastered brick walls and a 125 mm RCC slab spanning one way onto an internal wall, 4.0 m either side. The roof slab bears on the outside walls. Storey height 3.0 m.

Assumed values (check unit weights in IS 875 Part 1): wall 5.0 kN/m² of wall area; slab 25 kN/m³ × 0.125 m = 3.125 kN/m², plus 1.0 kN/m² floor finish = 4.125 kN/m²; imposed load 2.0 kN/m² (Table 1, i(a)1). Loaded width: 4.0 / 2 + 4.0 / 2 = 4.0 m.

Service load: 46.5 + 8.0 = 54.5 kN/m. IS 1905 checks load-bearing masonry against permissible stresses under this unfactored load, and the footing width comes from it and the soil's safe bearing capacity.

Design load for RCC members (IS 456:2000, Table 18, limit state of collapse): 1.5 × (46.5 + 8.0) = 81.8 kN/m. Use this for a plinth beam or an RCC footing under the wall.

Most new houses in India are RCC frames with brick infill. The method is the same: the slab load goes to the beams by loaded width (or by the 45° triangle and trapezium split for two-way slabs), infill walls become a dead line load on the beam below, and the beams take it to the columns.

Clause 3.2.1 lets you reduce the imposed load on columns, load-bearing walls, piers and their supports and foundations, depending on the number of floors they carry. Clause 3.2.2 lets beams take 5% less for every 50 m² they support, up to 25%, but not roof beams. Neither applies to every occupancy, storage among them. Check the clauses and their table before you use them.

• Using 1.5 kN/m² for an ordinary house. That value is only for low-income dwelling units built to IS 8888.
• Forgetting the 1.5 kN per metre line load at the outer edge of a balcony.
• Using 0.75 kN/m² for a flat roof that people can reach. With access it is 1.5 kN/m².
• Using the 1 kN/m² partition allowance for heavy brick walls.
• Adding factored and unfactored loads in the same total.