CROSS Safety Report
Reduced partition loads on proprietary joists
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A reporter believes that a number of proprietary joist manufacturers are using a reduced partition allowance for the engineered joist design.
Key Learning Outcomes
For civil and structural design engineers:
Where it is shown that the actual weight of a partition exceeds the loads given in standards and codes of practice, the actual weights should be used
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A reporter believes that a number of proprietary joist manufacturers are using a reduced partition allowance for the engineered joist design. The load used is quoted in the code of practice for engineered wood products. Whilst carrying out structural checks on several designs the reporter noticed that the load allowance is less than he would normally have used. They are concerned that this may be missed by contractors commissioning the floor design without an engineering check on the assumptions that have been made and wondered if anyone else has observed this too?
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It is assumed that the code of practice referred to is, 'Engineered Wood Products - Code of Practice' by the UK Timber Frame Association (January 2007). This applies primarily to new residential buildings and structures, although it states that the principles can be applied to other classes of structure. The minimum load for non-load bearing partitions, applied to single occupancy domestic floors is given as the more onerous of 0.64kN/m line load or 0.22kN/m2 uniformly distributed load (UDL).
The weight of a timber stud partition with 12.5mm plasterboard both sides is given as 27kg/m2 in TRADA Technology Timber Frame Housing: UK Structural recommendations. For a wall 2.4m high, this equates to around 0.64kN/m, as above. The document goes on to say that the floor designer is responsible for determining the partition loads on a floor.
Where it is shown that the actual weight of partition exceeds the loads given, the actual weights should be used. It also states that reference should be made to BS 6399-1 or BS EN 1991-1-1 for partition loads for floors of other than single occupancy domestic dwellings. Where partitions are envisaged, but their location is not known, an allowance of 1/3 of the load/m run of the finished partition should be applied as a UDL. This is consistent with the above. However, for office floors this UDL should not be less than 1.0kN/m2. The load to be applied thus depends upon the use of the building.
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