All timber sold and used for structural purposes in South Africa must meet the strength requirements for stress grade 5 as a minimum. Timber and laminated beams that do not meet the relevant grade requirements are not legal or safe for use as structural timber.
A glued laminated timber (glulam) beam is a structurally engineered wood product made by using moisture-resistant structural adhesive to glue and press layers of wood pieces to form a beam.
The high strength and dimensional stability of laminated timber (glulam) allow beams and arches to span large distances without intermediate columns. They provide more aesthetic and design flexibility than traditional timber truss construction. The size is limited only by transportation and handling constraints
However, designing and manufacturing laminated beams is more complicated than simply glueing some planks together. It is a meticulous process of timber engineering and documented quality assurance.
Consumers need to know that all structural laminated timber beams must comply with the minimum requirements outlined in SANS 1460: Laminated Timber. The supplier must stamp each beam to indicate the grade and the relevant accredited authority.
“Unfortunately, due to ignorance or to cut corners and costs, some people do not use structural laminated beams properly. They ignore important factors like the load-bearing ability or capacity of the beam,” says Abe Stears, managing director of South African Technical Auditing Services (SATAS).
Tests conducted on laminated timber beams by Prof Walter Burdzik at the University of Pretoria found that many did not comply with the South African National Standards (SANS) requirements.
“The manufacture of structural laminated beams in compliance with SANS 1460 is a costly process. This is why some unscrupulous contractors may use inferior imported or falsely labelled structural wood products that do not meet the required standards for strength or quality for structural applications,” explains Stears.
“The knock-on effects of this are potentially devastating. Cheaper alternatives could result in product failure a few years after construction. In most instances, the responsibility of repairs and related costs would befall the unsuspecting building owner,” he warns.
Testing and certification
The only way to demonstrate grade compliance is through certification by an ISO 17065-accredited certification body or a registered structural engineer. In South Africa, only SATAS and the South African Bureau of Standards (SABS) are accredited by the South African National Accreditation Systems (SANAS) to certify structural laminated timber.
The manufacturer must provide documented and verifiable evidence of using controlled conditions and processes. Certified glulam beams display information like the stress grade, certification mark of the certifying body, manufacturer’s trade name and the application class.
Stears reminds architects, engineers and public procurement officers only to specify certified structural timber that complies with SANS 10163: The Structural Use of Timber, and the National Building Regulations, SANS 10400.
“Ultimately, structural timber certification indicates where the beams can be used and provides assurance of correct application and traceability,” remarks Stears.