Sadly for the profession, very few engineers are truly comfortable designing in timber. Fewer still are confident dealing with nail-plated timber trusses. At Project X Solutions, we’ve been doing both for decades.

Every so often, we’re called to a job where a truss has failed—either at the nail plate or occasionally within the timber itself. In the last year or two, we’ve noticed an uptick in these cases.

Paul runs a forensic engineering workshop through the Engineering Training Institute of Australia. The phrase he’s coined to summarise this field is: “Every structure has an expiration date—unless intervention hits reset.”

Our working theory is that many of these trusses have simply reached their expiration date. A common theme? Tiled roofs without sarking, aged between 20 and 30 years. We believe that fluctuations in humidity—caused by the free flow of moist air through gaps in the tiles—lead to micro shrinkage and swelling of the timber. Over time, this movement ejects the nail plates.

Once the timber members part ways from their partners, the truss loses its structural integrity and is at risk of collapse. Many trusses stay upright only because they’ve landed on internal walls that were never designed to be load-bearing.

There is usually a solution short of full replacement, but it requires inspection (in what is often an awkward location), detailed engineering assessment, and custom repair design.

To date, we haven’t found any other consulting engineers who specialise in this work. If you need assistance, contact us.