Prefabricating methods utilising cross-laminated timber (CLT) technology are becoming an increasingly-popular addition to off-site construction.
A quicker and greener alternative to traditional concrete or steel-framed builds, the market for CLT has increased threefold over the past 24 months.
The building’s innovative design and use of the latest construction techniques and materials, such as CLT, have been dominant features of the build process
The technology, also known as X-LAM, is a structural two-way spanning timber panel that can be used to form wall, roof and floor panels as well as shear walls. It is produced in a similar way to glulam by stacking a number of layers of timber, known as lamellas, at 90º to the layer below and subsequently gluing them to create panels of up to 24m in length and 2,950mm in width, which can encompass between three and seven layers.
Available in various sizes, they are increasingly being utilised within off-site construction for building entire structures very quickly – vital in the healthcare environment, where services often need to continue uninterrupted during construction work.
As they are so lightweight, foundations can be smaller and there is little waste.
Also a key consideration for the medical sector, where organisations must cut carbon emissions by 80% by 2050, is the fact the panels are readily available, renewable and sustainable, making achieving the necessary high BREEAM ratings much easier.
Overcoming the barriers
Nick Milestone, managing director of B&K structures and a member of the Built Environment Hub, said he had seen a major growth in the use of CLT within healthcare construction.
Responding to this, B&K Structures is working with Austrian manufacturer, Binderholz, to develop technology to aide cross-laminated timber specification and design.
The CLT Construction Specifier is a free-to-use ground-breaking online specifying system developed to help validate and support early-stage calculations. It provides a risk and cost-free way for designers, engineers and architects to investigate cross-laminated timber as a structural solution.
The designers wanted to create a building that expressed a lightness and natural feeling of ‘wellbeing and wellness’, rather than merely being a place for curing the sick
Milestone said: “The lack of CLT performance information has been a barrier to specification and this open-source online tool will enable construction professionals to meet prerequisites of the build to deliver exacting thermal, fire and acoustic performance - eliminating the gap between design expectations and as-built results, while eradicating the costly risk of over-engineering.”
B&K Structures sold 8,000m3 of CLT panels in 2013 and 4,000m3 in 2012. Originally a steel structure specialist, it now makes up 50% of the firm’s turnover, compared to just 20% three years ago.
CLT was utilised in the development of The Kirkley Health Campus in Suffolk. Designed by Frank Shaw Associates, the £6m facility was constructed off-site by Kier.
Sean Perry, strategic projects manager for NHS Property Services East Anglia, which led the project, said: “The building’s innovative design and use of the latest construction techniques and materials, such as CLT, have been dominant features of the build process.”
Speed and accuracy
It was also specified for the superstructure of Cranleigh Health Centre in Surrey. Supplied by Stora Enso in conjunction with specialist timber engineers, Eurban, the method was chosen for its speed and accuracy, along with ease of access for material deliveries to the site, which was constrained by its central location on the edge of the village's main car park.
A spokesman for Stora Enso said: “CLT's airtightness was a key consideration for the new building, which has been designed to meet the current Health Technical Memorandum and Health Building Notes as well as exceeding Building Regulation Standards in terms of U values for the fabric.
“The designers wanted to create a building that expressed a lightness and natural feeling of ‘wellbeing and wellness’, rather than merely being a place for curing the sick. The specification of CLT was key to achieving this and much of the internal face of the superstructure has been left exposed.”
CLT is generally manufactured from spruce wood, but can also be taken from white fir and Douglas fir trees and can be manufactured for exposed or internal areas and clad in any number of materials.