Timber is a central material to offsite construction and one of the leading mainstream, renewable, low-carbon building materials. Timber’s sustainable credentials and role in the circular economy are commonly understood and with the use of FSC and PEFC-certified timber, responsible sourcing is of huge importance.
Structural timber has developed hugely in recent years. Timber can be used in several slightly different build systems including engineered timber solutions such as cross laminated timber (CLT) and glulam, as well as timber frame, structural insulated panels (SIPS) and associated open and closed panel systems. Timber has impressive thermal and acoustic performance levels as well as huge aesthetic appeal to architects and building designers.
The use of solid wood solutions such as CLT and glulam has revolutionised the way that timber is used in a multi-storey setting with buildings across the globe now part of the ‘tall timber’ phenomenon. CLT structures of 10 storeys have already been constructed in the UK. Current knowledge supports up to 15-storey designs. Canada currently holds the world record for the world’s tallest timber tower with the 18-storey Brock Commons Tallwood House at the University of British Columbia in Vancouver.
Cross Laminated Timber (CLT)
CLT is a structural two-way spanning timber panel solution that can be used to form walls, roof and floor panels as well as shear walls. CLT 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 CLT include its large bi-axial and ﬂexural loadbearing capacity when used as a wall or slab, together with its superior acoustic and structural performance properties. CLT panels have huge structural potential and are suitable for most building types.
Made from layers of parallel timber laminates glued together, glulam sections are now frequently used in the construction of all types of building including supermarkets and swimming pools. Attractive with design appeal, glulam beams provide large-span structures without supporting columns, with the addition of lots natural light. Solid wood products such as CLT and glulam are natural, renewable and are far less energy-intensive to produce than concrete and steel. Timber involves very little waste during production and huge amounts CO2 will still be stored/captured after the production process.
Timber frame can consist of wall panels, alongside floor and roof panels – often referred to as cassettes. These can also be open panel or closed panel. Open panels are timber frame wall panels, comprising studs, rails and sheathing on one face and a breather membrane. Closed panels also include plasterboard linings on the faces of the panel, a vapour barrier and breather membrane. Closed panels may also include fitted windows, openings for doors and service routes. Manufactured in factory conditions, these cassettes and panels are brought to site and fixed together to form a rigid load-bearing superstructure. These consist of timber studs and beams, stiffened on one side with oriented strand board (OSB) and plasterboard.
Structural Insulated Panels (SIPS)
SIPS are primarily a timber-based panel that consists of two parallel faces – usually oriented strand board (OSB) or cement-bonded particleboard – with a rigid core of polyurethane (PU) foam or expanded polystyrene (EPS) inside, SIPS are a cost-effective and energy-efficient solution to a wide range of building types and can provide airtight walls and roofs. SIPS panels also offer high levels of insulation due to the use of the in-filled material. Properly used, SIPS needs no other structural frame supporting them. SIPS offer the efficiency of structural and thermal performance within one product, delivering U-values as low as 0.10 W/m2k.