s the Government-commissioned Farmer Report, entitled ‘Modernise or Die’, creates ripples across the construction industry, with Author and Cast CEO Mark Farmer making a strong case for change, I believe the start of this transformation is already underway with innovations in engineered timber leading the way. We define engineered timber – or solid wood, as it is also known – as heavy, structural timber elements made up by bonding timber lamellas together to form units with known structural characteristics.
There are two main structural solutions – cross laminated timber (CLT), formed by gluing lamellas into a wide and long panel and glued laminated timber (GLT), formed by gluing lamellas on top of each other to form a beam.
Cross laminated timber
Cross laminated timber is a structural, two-way spanning timber panel that can be used to form walls, roof and floor panels as well as shear walls. Cross laminated timber panels are available in spruce, Douglas fir and larch and can be supplied as FSC- and PEFC-certified.
It is produced by laminating and finger-jointing soft wood timber lamellas at 90° to the layer below – this can encompass between three and seven layers. The structural benefits of cross laminated include its large bi-axial and flexural load-bearing capacity when used as a wall or slab, together with its superior acoustic and performance properties. Cross laminated timber is five times lighter than concrete and also distributes concentrated loads as line loads at foundation level, which reduces the requirement for localised pad foundations.
Cross laminated timber structures of 10 storeys have already been constructed in the UK. Current knowledge supports up to 15-storey designs, but the feasibility of building a timber structure up to 30 storeys tall has been investigated. Structures are typically built using a ‘platform frame’ approach, meaning that walls are temporarily braced with raking props before floor panels are lowered onto them and fixed.
In addition to excellent sustainability credentials, good thermal insulation performance and sound insulation properties, it is speed of construction where cross laminated timber is in a class of its own. Cross laminated timber, as a rapid, robust and reliable off-site manufactured solution, delivers many benefits during the construction process and beyond. From reducing loading on foundations through to impressive thermal, acoustic and airtightness performance – cross laminated timber construction enhances projects across all sectors. Manufactured to exceptional levels of accuracy in factory controlled conditions ensures minimal defects and improves construction and project delivery time, reducing costs and maximising efficiency on all levels – providing cost and programme certainty.
However, the benefits do not end after the construction phase. Due to the enhanced performance values and robust nature of cross laminated timber, the ongoing lifecycle costs of the building is vastly reduced through less maintenance requirements and lower energy consumption.
Glued laminated timber
Whilst maximising sustainability credentials as a carbon neutral and renewable resource, engineered timber products are often selected to be exposed for aesthetic reasons. One of the most versatile engineered wood product materials is glued laminated timber or ‘glulam’.
Glulam is an engineered wood product, manufactured from layers of parallel timber laminations – normally spruce or pine but occasionally more durable timber species such as larch, Douglas fir or even hardwoods such as oak or sweet chestnut are used. Individual laminates can be finger-jointed to produce long lengths in accordance with the requirements of BS EN 385:20013. One of the greatest advantages of glulam is that it can be manufactured in a wide variety of shapes, sizes and configurations. Beams wider than normally available can be manufactured by laying boards of different widths side by side and reversing each layer so that there is an overlap and no straight-through vertical joint.
In addition to straight prismatic sections, beams can also be single tapered, double tapered and bevelled. Curved profiles range from a simple curved beam to a pitched and tapered curved beam, to a complex arch configuration. Curved glulam is manufactured by bending laminates on formers before being bonded together with adhesive, clamped and cured.
With its high load-bearing capabilities and high dimensional stability, glulam can be manufactured up to 50m in length and 4.5m in width. A variety of different structural components can be formed including parallel beams, pre-cambered beams, sloped beams with a straight or arched bottom chord, curved beams, flitch beams and trusses.
Large open areas can be created using glulam portal frames – arches and spans are only limited by the length and weight of the glulam components due to fabrication and transport restrictions, with site conditions occasionally being a further constraint. In some instances, roof areas exceeding 100,000m2 have been constructed using glulam framing.
From my professional standpoint, engineered timber is gaining traction across the industry and glulam offers almost unlimited possibilities in the creation of structures that combine functional and load-bearing characteristics, to meet architectural aspirations. Developed to meet the high requirements of modern timber construction, glulam optimises the structural values of timber by taking advantage of its exceptional aesthetic characteristics whilst enhancing its structural performance thus creating elegant and refined structures.
The time is right for the construction industry to embrace innovative timber technology and off-site techniques, supported by design for manufacture and assembly protocols, to develop better buildings at a rapid rate to enhance lives, minimise the environmental impact and reduce energy costs for building owners and occupiers for many years to come.
