Laminated veneer lumber (LVL) is an engineered structural product which is made by bonding wood veneers together that have been peeled or sliced, dried and then laminated together with a structural adhesive, which is commonly phenolic based. This forms a solid member of end sections and length.
The grain direction of each veneer is usually orientated parallel to the length of the piece but may be cross-banded for speciality applications. Because of its laminated structure dispersing strength reducing characteristics more evenly, LVL has higher bending strength and stiffness than the equivalent solid timber section of the same species.
“LVL has many advantages over traditional building products, including uniformity of engineering properties, high strength-to-weight ratio and availability in long lengths,” says Peter Hyne, general manager wholesale at Hyne.
LVL products are often manufactured from Maritime Pine or Radiata Pine. According to Forest and Wood Products Australia, it is on average 50 per cent stiffer and two to three times stronger than the sawn timber from which it is manufactured.
Around 70 per cent of LVL used in Australia is for residential purposes, according to Wesbeam. It is most often used for non-appearance structural applications such as floor joists and bearers, lintels, roof beams and rafters. The only area where LVL is not recommended for use is in exterior or exposed applications.
The market trends, according to Hyne, are in areas such as new home design with the desire for large open plan spaces. “With their consistent structural properties and long lengths, LVL products allow architects and designers more freedom to achieve their vision.”
Currently, only a handful of companies in Australia manufacture LVL products, including Hyne, Wesbeam and futurebuild, a divison of Carter Holt Harvey. The Hyne I-Beam T2 is a combination of timber components and technology to form an ‘I’ section which is suitable for use as floor joists, rafters, lintels, purlins and girts. It is produced using pre-treated finger jointed pine flanges and H2 (permethrin in glue) 9.5 mm oriented strand board (OSB) structural panel webs. All components are assembled using exterior grade adhesives.
All Hyne I-Beams are T2 treated for termite protection and is less than half the weight of comparable solid timber sections. The company also manufactures Tasbeam 18C, which is a light-coloured hardwood glue laminated timber beam which is available in both structural and appearance grades. It is manufactured from the ash group of eucalypt species and is suitable for use as lintels, roof beams and as high-load bearers.
Wesbeam manufactures its LVL products from Maritime pine, which it says is 20 per cent denser than traditional pine. “Every layer of wood passes through ultra-sonic sensors and lasers to determine which application it is best suited to. Each product then has its own lay-up pattern and veneer type, to ensure maximum strength,” says Denis Cullity, sales and marketing manager at Wesbeam.
“In relation to structural beams, the coefficient of variation (CoV) is a measure of the variability in a particular structural property. Structural products with a low CoV behave more closely to the design with predicted behaviour, whereas products with higher CoVs tend to vary to a higher degree to their predicted behaviour. Universal steel beams have similar CoVs to LVL, whilst CoV of MGP pine is at least twice that of LVL. Choosing products with a low CoV, such as LVL, will give you a more reliable job.”
futurebuild also has several LVL products. It developed Hybeam to replace solid timber as a lightweight floor joist. According to Michael Murphy, technical manager of futurebuild, Hyjoist involved a complete re-engineering of the Hybeam range in order to provide more options in floor design. The range features 10 section sizes with three sections available for the key floor depths of 240 mm and 300 mm where a larger span range is sought. The range also introduced economy joists in depths 240 mm, 300 mm, 360mm and a 400mm deep section.
futurebuild also manufactures Hyspan H2-S, a termite treated version specifically for areas of Australia south of the Tropic of Capricorn. The glue used to bind the veneers together contains bifenthrin, which means the treatment is 'locked up' in the glue line so cutting or sawing is not an issue.
Another of the company’s products is Hychord, which is manufactured from Radiata pine. The veneers are ultrasonically graded and sorted for stiffness and laminated into 12 layers. The moisture content of the product is 7 per cent to 15 per cent and the density is around 600 kg per m3.
Eventually, Hyne sees LVL and other engineered timber products replacing sawn timber products in some applications. He says: “It makes sense for LVL or similar engineered products to replace solid timber for most structural applications. But solid timber will remain the premier choice for exposed applications requiring an appearance grade product.”
