Building Regulations 2000, Approved Document A, Structure, requires roof and wall panel systems to be designed to withstand the combined effects of dead, imposed, and wind loads, and transmit them safely and without excessive deformation to the support structure.

Design loadings can be determined for any location in the UK using the following standards:-

BS6399: Part 1: 1984 Dead & Imposed Loads
BS6399: Part 2: 1997 Amendments No.1 Wind Loads
BS6399: Part 3: 1988 Imposed Roof Loads
BS5502: Part 22: 1993 Agricultural Buildings

The loading can be positive for snow loads and wind pressure, or negative for wind suction and uplift. The values will vary depending on the position of the cladding on the building. A cladding must be selected which is strong enough to span between the purlins, rails or structure when subjected to the design loading. It must also be secured with sufficient fasteners to ensure it stays attached to the frame under wind suction loads.

Calculating design loadings can be complex and would normally be carried out by a qualified engineer. The following example indicates how the loadings would be determined for a typical building, and how the cladding and fasteners are selected. It is for general guidance only.

Design Loading Calculation Example

The industrial unit shown below is to be built on the outskirts of Birmingham. It is to have a steel frame and will be clad with KS1000 RW roof and KS1000 MR wall Panels.

Roof Loading

Dead Load - BS6399: Part 1: 1984

This load is the total weight of the materials themselves and is normally supplied by the product manufacturer.

KS1000 RW roof panel - 80mm thick
Weight = 11.5 kg/m² = 0.11 kN/m²
The design code also allows for any service and access loads.

In this example the roof is assumed to have no services or access loads.

Snow

Imposed Load - BS6399: Part 3: 1988

The standard covers the load caused by snow lying on the roof taking into account the location of the building, height above sea level and the effects of redistribution, ie. drifting.

For this example:

Basic snow load (Birmingham) sb = 0.6 kN/m².

Site snow load (undrifted snow at site altitude), so = sb for an altitude < 100m.

For a roof with no access other than for cleaning and maintenance the imposed load to be used for each part of the roof is the maximum for the following conditions:

1. Uniformly distributed snow load
2. Redistributed snow load
3. Uniformly distributed load of 0.6 kN/m² (roof slope <30°)
4. Concentrated load of 0.9 kN

Therefore considering condition 1, snow on roof sd = ui x so, where ui is the shape coefficient.

From Figure 3, in the standard ui = 0.8 for snow on a roof < 30°. Therefore sd = 0.8 x 0.6 = 0.48 kN/m².

Considering condition 2, for roof slopes < 15°, ui = 0 The concentrated load of 0.9 kN is not critical for insulated panels so the worst loading condition for the building is therefore condition 3.

Design snow load sd = 0.6 kN/m².