Imposed floor loads for houses in South Africa (SANS 10160-2)

SANS 10160 is the South African loading code, "Basis of structural design and actions for buildings and industrial structures", published by the South African Bureau of Standards (SABS). Part 1 sets out limit states design and the load combinations. Part 2 covers self-weight and imposed loads. Other parts cover wind (Part 3), seismic actions (Part 4) and geotechnical design (Part 5). The current Part 2 is SANS 10160-2:2011, Edition 1.01, which includes Amendment 1A of October 2011.

Part 2 gives minimum characteristic imposed loads by category of use. Table 1 covers residential, social, commercial and administration floors (categories A to D), Table 2 industrial use and storage (E), Table 4 traffic and parking areas (F and G) and Table 5 roofs (H, J and K). Loads are in kN/m² (1 kN/m² = 1 kPa). Where the actual use gives a higher load, design for it.

Many houses are not designed from SANS 10160 directly. SANS 10400, the Application of the National Building Regulations, gives deemed-to-satisfy rules for houses: for example, SANS 10400-K sets wall thicknesses, panel sizes and openings for masonry walls that may be built without calculation, within its limits. SANS 10400-B requires the structural strength and stability of a designed structure to be assessed with actions from SANS 10160. That is when the values on this page apply: when an engineer designs the house or a part of it, such as a suspended slab, a beam or a wall outside the deemed-to-satisfy limits.

These are minimum characteristic values (qk). The tables also give concentrated loads (Qk) for local checks; this page lists the uniform loads only.

SANS 10160-2 treats movable partitions as an extra uniform imposed load on the floor, added to the category value. It uses the method of EN 1991-1-1: the allowance depends on the partition's self-weight per metre of wall, and lies between 0.5 and 1.2 kN/m² for partitions weighing up to 3 kN/m.

Heavier partitions, such as the brick or block internal walls usual in South African houses, are well over 3 kN/m. Carry them as permanent load at their actual weight, as a line load where they stand, not as a uniform allowance.

Most pitched house roofs are inaccessible (category H). Use 0.25 kN/m² for a member whose loaded area is over 15 m², such as a truss or a wall carrying a large roof area, and the higher small-area values of H1 and H2 for battens, purlins and other members carrying under 3 m². The inaccessible roof load is not combined with wind. Check wind uplift and the roof fixings to SANS 10160-3 separately.

A double-storey house. A 150 mm reinforced concrete first-floor slab spans 4.0 m from each exterior wall onto an interior load-bearing brick wall on the ground floor, so the wall's tributary width is 4.0 / 2 + 4.0 / 2 = 4.0 m (simple spans; a slab continuous over the wall sends more than half its load to the middle support). The roof trusses span from exterior wall to exterior wall, so this wall carries no roof load. Ground-floor storey height 2.7 m.

Assumed values (check them for the actual build-up): reinforced concrete 25 kN/m³, so the slab weighs 0.15 × 25 = 3.75 kN/m²; screed, floor finish and ceiling 1.0 kN/m²; 230 mm plastered brick wall 4.5 kN/m² of wall area. Imposed load 1.5 kN/m² (SANS 10160-2 Table 1, A1). The upper-floor partitions are lightweight drywall, under 3 kN/m, and their positions are not fixed, so a movable-partition allowance is added, taken at the top of the range, 1.2 kN/m².

STR combination: 1.2 Gk + 1.6 Qk = 1.2 × 31.15 + 1.6 × 10.80 = 37.38 + 17.28 = 54.7 kN/m.

STR-P combination, the check for structures where the permanent load dominates: 1.35 Gk + 1.0 Qk = 1.35 × 31.15 + 1.0 × 10.80 = 42.05 + 10.80 = 52.9 kN/m.

STR governs, at 54.7 kN/m. Use it to check the wall, a lintel or beam under it, and the foundation's strength. The unfactored total, Gk + Qk = 31.15 + 10.80 = 42.0 kN/m, is the figure usually compared with the soil's allowable bearing pressure to size a strip footing.

STR-P comes close here because masonry and concrete make the permanent load large: Gk is 2.9 times Qk. In a heavier building, or for the foundation with its own weight added, STR-P can govern. To continue down to the footing, add the ground-floor slab if it bears on the wall, the foundation wall and the footing itself.

• Using the Eurocode factors 1.35 Gk + 1.5 Qk. SANS 10160-1 uses 1.2 Gk + 1.6 Qk, with a 1.35 Gk + 1.0 Qk check for dominant permanent load.
• Skipping the STR-P check on heavy masonry and concrete houses, where the permanent load is large compared with the imposed load.
• Designing a balcony for the 1.5 kN/m² of the rooms it serves. Category A4 balconies take 4.0 kN/m².
• Using 0.25 kN/m² for battens and purlins. That value is for loaded areas over 15 m²; small members take 0.75 kN/m² (construction) or 0.5 kN/m² (maintenance), with interpolation between 3 and 15 m².
• Treating a flat roof used as a terrace as an inaccessible roof. A roof used by people takes category J, or K at the value of the floor category it serves.
• Using the movable-partition allowance for brick or block walls. It applies to partitions up to 3 kN/m; carry heavier walls as permanent line loads.
• Assuming the SANS 10400 deemed-to-satisfy rules cover a house outside their limits. Beyond them, the structure must be designed with SANS 10160 actions.