IBR Roof Sheeting

IBR, short for inverted box rib, is a trapezoidal profiled metal sheet used for roofs and walls of houses, farm buildings, warehouses and factories in South Africa and neighbouring countries. It is the southern African counterpart of the box-profile or trapezoidal sheets used elsewhere.

Profile

Manufacturers' data for a typical South African IBR sheet give:

• Effective cover width: 686 mm (27 in); overall width 740 mm (29 in).
• Broad flute pitch: 171.5 mm (6.75 in), with stiffening ribs between the main ribs.
• Thicknesses: 0.40, 0.47, 0.50, 0.55, 0.58 and 0.80 mm (0.016 to 0.031 in).

Materials and finishes

IBR is roll-formed from steel coil with:

• Galvanised zinc coatings (Z150, Z200, Z275).
• Aluminium-zinc coatings (AZ150).
• Pre-painted finishes on coated steel.

Pitch and spans

The minimum recommended roof pitch is 5 degrees for roof slopes shorter than 30 m (98 ft) and 7.5 degrees for longer slopes. Recommended maximum purlin spacings for roofs, from one manufacturer's data, are:

Sheet thickness	Single span	Double span
0.40 mm	1.25 m (4.1 ft)	1.40 m (4.6 ft)
0.47-0.50 mm	1.65 m (5.4 ft)	1.95 m (6.4 ft)
0.55-0.58 mm	1.75 m (5.7 ft)	2.10 m (6.9 ft)
0.80 mm	2.25 m (7.4 ft)	2.50 m (8.2 ft)

Wall rails can be spaced further apart, for example 1.70 m (5.6 ft) single span for 0.40 mm sheet. These are general guidelines, and an engineer's design is advised for specific buildings.

Use

In South Africa, corrugated iron or zinc sheet, the census category that includes profiled steel sheet such as IBR, was the most common roof material recorded in the 2011 census sample file.