Trussed rafter installation and the implications for scaffold erection on newbuild sites

Robert Candy, Chief Executive of the Scaffolding Association, discusses the scaffolding considerations that need to be made when installing trussed rafters on newbuild projects.

When it comes to trussed rafters, it has traditionally been common practice to attach them to the scaffold structure for stability during installation. The process had previously been animated by the Trussed Rafter Association (TRA) and promoted in their guide “How to safely install Roof Trusses” on their website. The document described the following method:

“Erect table lifts at both gable ends. Ensure the scaffold is constructed in accordance with a design drawing based on engineers’ calculations to safely support the anticipated loads for this site. For further information on truss weights and sizes, contact your trussed rafter supplier.”

This statement, which although technically correct, does not provide a detailed enough explanation of the procedures that would be required to enable the installation works to be undertaken in line with current guidance. Following an initial consultation between the TRA and the Scaffolding Association (SA) the guidance has now been suspended and is under review.

So, what should we be considering when using scaffolding to enable the installation of roof trusses?

Design

When you begin to break down the installation process of roof trusses into stages, it becomes clear that the type of scaffolding structure that may be needed could be classed as a shoring or support scaffold. This means that bespoke designs will be required and developing a detailed design brief is key. When developing the temporary works designs, consideration should be given to:

• House type

• Height of the truss installation

• Site location for wind calculations

• Weight of a complete pack of trussed rafters, which could be up to 500kgs

• Stage of installation at which the trussed rafters become self-supporting

• Dimensions, surface area and weight, of the trussed rafters

• Bracing and fixing components between the scaffold and the trussed rafters

• Amount of space available onsite for buttresses and rakers

By producing bespoke drawings for each house type, truss type and given windspeed location on a newbuild site, contractors can be confident that safe and suitable solutions are available. These designs would then need to be agreed and approved by the Temporary Works Coordinator appointed for the site.

Control of Temporary Works

A robust temporary works plan should be created, clearly defining the roles and responsibilities of those involved in the operations. Issues to consider include:

• Who is in control, and at what stage of the process?

• Does the scaffold contractor have the relevant insurance and competence to erect shoring scaffolds?

• Will the scaffold contractor build the structure and then hand over to the building contractor?

• Will the carpentry contractor be responsible for installing the bracing required to complete the supports for the trusses?

• Does the carpentry company have the relevant temporary works competence and insurance?

Erection and Installation

A full site-specific risk assessment and method statement is a standard procedure, undertaken before any work commences, however specific consideration should also be given to areas like:

• The space required for additional buttress scaffolds, and/or kentledge, and/or rakers at each gable end

• Transporting onsite the extra equipment that may be required for additional buttress scaffolds, and/ or kentledge, and/or rakers at each gable end

• Installation of trussed rafters should be time-limited so they are not left unattended until the structure is self-supporting

• Sudden or extreme changes in weather conditions

• A bespoke scaffold structure of this nature would require an NVQ Level 3 Scaffolder to erect and sign off

Until the TRA re-issue their installation guide, which will consider the implications of imposing trussed rafter loads onto a scaffold structure, you should as a minimum ensure that the points discussed have all been considered.