CROSS Safety Report
Building Regulations submission for a small house
This report is over 2 years old
A reporter who is a small builder shares their experience on inadequate design calculations they received for a small house.
Key Learning Outcomes
For all built environment professionals:
It is important to recognise and know the boundaries of your expertise and work within the limits of your competence
Be aware that Health and Safety legislation places duties on individuals as well as companies to ensure that they do not put people at risk of harm
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The reporter is a small builder who used to be a building control officer and he was given a design, on headed paper with the Institution of Structural Engineers (IStructE) logo on the top, for a single storey house extension. The roof is pitched and open and supported on inclined rafters resting on longitudinal beams about halfway down the pitch.
The bottom of the rafters’ rest on the inner leaves of blockwork walls, 2m high (no tie). There are no details of how the load gets vertically into the longitudinals (depending on the detail the load is inclined or vertical). There is no ridge member to take the inclined rafter loads, there is no way lateral loads from wind are carried, there is no way the outward thrust at the top of the wall is accommodated (gravity or wind).
The longitudinals spanning 5m and carrying the whole roof are described as ‘6-inch timber rafters’. In response to a protest, a ridge has been added with a one page calculation (computer generated) which just says use 300 x 150 rafters (evaluated to 4 decimal places so it must be right) (still no lateral wind load).
Bearing stress is worked out to 3 decimal places of N/mm2, there is of course no detail or definition of the support detail and no minimum bearing length and no pad detail. On the plus side the notes say all workmanship has to be carried out to the satisfaction of the Local Authority Building Control Officer: no worries there then.
Moreover, concludes the reporter, we can relax, there is radon protection despite this being in a limestone area and miles away from the nearest decomposing granite.
Expert Panel Comments
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CROSS continues to be concerned that anyone can make a submission to building control with no requirement for competency. Here the situation has been compounded by the person making the submission apparently purporting to be in some way associated with the Institution of Structural Engineers.
Here the situation has been compounded by the person making the submission apparently purporting to be in some way associated with the Institution of Structural Engineers
A letterhead can give an indication of whether a design is likely to be acceptable but is not a reliable indicator. In this case it appears that the design had been approved despite the glaringly obvious flaws. If submissions could only be made by approved designers, then cases such as this could be avoided.
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