Skip to main content

CROSS Safety Report

Building Regulations submission for a small house

Report ID: 91 Published: 1 January 2008 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.


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

Full Report

Find out more about the Full Report

The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.


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

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

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.

Submit a report

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.