“My dad told me about them!”: TDA roof trusses

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TDA roof truss diagram

Before we had the trussed roofs we commonly use today, the prototype was developed in the 1950s when resources were still in short supply following the war.

The roof was made up of 'TDA' trusses positioned at 1.8 to 2.4m centres with rafters and ceiling joists between them at 450mm centres and could span up to 8m:

Roof truss diagram
Picture courtesy of R Chudley & R Greeno

The TDA trusses were built on-site using toothed plate connectors and were based on standard designs that were published by the Timber Development Association (TDA), the forerunner of the Timber Research And Development Association (TRADA).

The trusses supported purlins and binders, which in turn supported rafters and ceiling joists.

They mirrored the principles of the impressive oak Queen Post and King Post trusses (below) used since the sixteenth century, but with much smaller timber sections and were not intended to be visible, as a ceiling was fitted beneath rather than at rafter level. Like trusses today, they can’t be modified without weakening the roof.

Queen Post and King Post trusses
Picture courtesy of Oaktimberframing.com

As timber development continued, they evolved into today’s roof trusses that use much smaller timber sizes at smaller centres but are restrained through additional bracing.

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Please Note: Every care was taken to ensure the information was correct at the time of publication. Any written guidance provided does not replace the user’s professional judgement. It is the responsibility of the dutyholder or person carrying out the work to ensure compliance with relevant building regulations or applicable technical standards.


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