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TFT Woodexperts Limited

Technical and Training Solutions for the Timber and Construction Industries

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The Acid Test

The performance of timber structures over a century old was the starting point for our site investigation services recently, when we were called in to look at the condition of a factory roof in the north of England. Bowstring, also known as ‘Belfast’, timber roof trusses has been used to create a Victorian factory roof, still extant today but potentially needing repair.


Frequently used in the expansion of factories across Britain at the height of the industrial revolution in the late 1800s, bowstring trusses feature an arched top with a horizontal bottom beam. They are deployed for their strength in compression and their ability to span wider distances. In Victorian times, it was still possible to get very long lengths of solid timber for roof spans. Yet the same engineering structure could also be used with shorter lengths, which encouraged its widespread use.


The Belfast trusses we were called in to inspect were in an environment where acidic processes were taking place in the factory below. Timber as a material tends towards the acidic. Acidic species like Douglas Fir, Oak and Pine have all been used in roofing applications, both today and in Victorian times. Timber resists an acidic environment and was sometimes used in preference to steel, which could corrode. Timber however performs less well when the environment is alkaline.


Luckily for the factory owner, the trusses were still in reasonable condition, the only wear and tear being caused by repeated leakage from guttering. Establishing the conditions and means for preserving historic timbers is part of our consultancy services, and one of the reasons behind our lead consultant, Jim Coulson, being on the Wood Committee of the conservation body, ICOMOS.


If you have a historic building or structure in need of assessment, please get in touch. Our extensive experience is at your service.

4 January 2018