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Are designers within TRA member companies a principal designer?

22nd March 2024

On 1 October 2023, new regulations came into force which define the duties of a principal designer under the Building Safety Act  2020 which is mandatory for all projects covered by the Building Regulations.

It is the responsibility of the client to take all reasonable steps to appoint designers and contractors with the necessary competence or organisational capability to carry out their roles.

Should a project have more than one designer or contractor, the client must appoint in writing a principal designer to be in control of the design work, and a principal contractor to be in control of the building work. On smaller projects where TRA members may be the only designer, you should be clear under which circumstances you may or may not be prepared to accept the Principal Designer’s role.

Principal designers’ duties

The Principle Designer has additional duties alongside their usual responsibilities as a designer and must be able to demonstrate that they are suitably qualified to fulfil the role. Additional duties include:

  • take reasonable steps to make sure all designers comply with their duties under building regulations
  • assess design work to make sure all designers produce designs that comply with relevant building regulations
  • work with the principal contractor and share information about planning, managing, monitoring and coordinating the design and building work
  • assist the client in providing information to others, if requested

Higher-risk building work

Any projects that are classed as a higher-risk building will have additional duties. Higher-risk buildings are classed as:

  • seven storeys or is at least 18 metres high
  • 2 residential units, or is a hospital or a care home

It is unlikely TRA members will be involved in the first category but do design and provide products for the second. The additional duties required for principal designers will include:

How will this affect designers within TRA member companies?

It is important to note that trussed rafter designers will not be expected to fulfil the role of principal designer other than potentially on smaller projects as identified above.

PD6693 (or SR 70 in Ireland) identifies the two critical people involved in the design stage, are the building designer, and the trussed rafter designer.

The Principal Designer is usually an architect or structural engineer who is appointed by the client to lead a project, whilst trusted rafter designers are considered structural component designers.

The trussed rafter or metal web joists they design, work together to form the structural framework of a roof or floor; the loads that are applied to those roofs or floors (the coverings, linings and insulation) are all, in most supply situations, determined and installed by others.

However, the thermal, acoustic and fire performance of the building these roofs or floors are installed within, are all outside of their control. In our national standards, the design aspects of these decisions, are the responsibility of the Principle Designer.

The responsibilities of the principal designer include ensuring the overall design work fully adheres to all relevant building regulations. This includes compliance with structural integrity requirements outlined in Approved Document Part A, as well as adherence to specifications for the building fire strategy as described in Approved Document Part B. Additionally, they oversee the use of appropriate materials and standards of workmanship.

As trussed rafter designs are two-dimensional, it is the Principle Building Designer’s responsibility to ensure the stability of the three-dimensional roof as a whole.

This means the trussed rafter designer details the individual trusses, but not the overall roof structure unless specifically engaged to do so.

More information can be found via the TRA’s Buyer’s Guide to Trussed Rafters.

To learn more about the principal designers’ duties, visit the government’s guidance on Design and building work: meeting building requirements.

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Trussed Rafter Association