Lendlease has embraced cross-laminated timber (CLT) for some of its major projects. Head of sustainability Jon Kirkpatrick explains why
Cobalt Place, a site completed in 2012 comprising of 104 residential units split over two sites in Battersea, south London, wears its sustainability credentials on its sleeve. The development’s dedicated website claims that CO2 emissions will be 25% less than homes built to current Building Regulations, for example.
It is one reason why the property and infrastructure group has used cross laminated timber (CLT) throughout Cobalt Place, the others being its structural qualities and the significant efficiencies it brings to construction.
A CLT panel consists of several layers of kiln-dried lumber boards stacked in alternating directions, bonded with structural adhesives, and pressed to form a solid, straight, rectangular panel. Similar in construction to plywood, with laminated layers of timber stuck together at 90 degrees, CLT has excellent rigidity, making it a very stable material to work with. Because of this there is little movement and it is has good loadbearing qualities. CLT can also be manufactured with great deal of accuracy, designed and built as it is in a factory and cut using laser-guided tools with very small tolerance or errors.
These qualities have impressed Lendlease so much that CLT is a major part of the £1.5bn development at Elephant & Castle and it is now seeking to use the material wherever it is appropriate.
Building4Change caught up with Jon Kirkpatrick, head of sustainability at Lendlease, to find out more.
What is Lendlease’s approach to CLT?
We are working on the philosophy of starting CLT as a design option as it’s a fantastic material to work with and opens up a whole new set of avenues and opportunities for us. But it is determined on a project-by-project basis: there is massive potential in London with safety, speed and build of construction as key drivers, however, it doesn’t really lend itself well for flexibility on commercial developments where large open plan spaces are needed. The use of CLT in our projects in London will not only allow us to achieve sustainability goals and contribute to safety but also speed of construction – so in terms of a method of construction it’s something we are looking at quite seriously.
What are the sustainability benefits over steel and concrete?
Firstly there is minimal wastage; in fact quite often the factories, particularly in Austria and Germany, use the offcuts to go back into the boiler system in order to power the mill. There is also minimal waste, minimal noise, pollution and dust on the construction site as it is delivered then simply bolted together. As a result, CLT is incredibly clean during construction, more so than with concrete builds.
Wood is also clearly great for embodied energy, effectively acting as a carbon store as opposed to materials that are taken out of the ground and processed like steel. It is a fantastic material in terms of water too, using 5.5 times less water per cubic metre (m3) over concrete. Plus, analysis from Lendlease’s Forte tower development in Melbourne showed there were 7.5 times fewer deliveries in terms of materials compared to concrete, so less impact on the road network.
Has Lendlease met resistance from residents, for example because of concerns around fire safety?
In Europe 80% of buildings under two storeys are made using timber and this trend is starting to develop around the world. In our experience, nobody in the UK has been refused a mortgage as a result of their home being built using CLT. On another project in Australia, we have demonstrated with residents using a blowtorch and a block of wood, challenging them to set it alight – to no avail.
Structurally are buildings constructed with CLT, lighter than steel and concrete?
Yes, and as a result you can have smaller foundations, which is useful on projects where you have poor ground quality or when you have to build over existing infrastructure, like the London Underground for example. The ability to build a lightweight structure is crucial, as we undertake more and more urban regeneration work, and having tools in our design arsenal like CLT allow us to take on complicated projects and unlock sustainable regeneration opportunities amidst a cityscape that has existing infrastructure, or needs to reduce the amount of downtime/impact on neighbouring communities. The speed and lightweight nature of CLT makes it perfect in difficult situations like these.
How long does it take to manufacture CLT off site and how long does it take to erect?
The manufacturing process is very quick offsite and the panel size is generally limited to the size of the footprint of transportation, typically trucks. The factory is processing tonnes of timber in a month at a phenomenal rate so the process rapidly moves through the mill in terms of the construction. Also it’s a much quicker to erect; for example, the 10-storey Forte tower in Melbourne was erected by five people. Each floor acts like a crash deck for the floor beneath that can be used for follow on trades to do electrics and pipework. Because of this CLT lends itself to difficult and complex projects and opens up avenues of design and development that you wouldn’t necessarily have given a complicated scenario such as poor ground conditions.
How difficult has it been to get a skilled workforce in the UK and where have you had to recruit?
The skilled workforce is quite small. The complex elements involve the crane drivers and different specialists to be able to work to tight constraints and sometimes recognise unsuitable work conditions such as high winds. Therefore we ended up training bank men and people onsite from a health and safety perspective. On Forte, we had one supervisor, two carpenters and two apprentices – all the hard work is done beforehand.
CLT is perhaps more associated with school buildings – do you see the market growing for CLT in residential markets?
The actual construction process is relatively simple regardless of the building type – after they have been linked up, it’s a case of bolting them together. When the project is designed properly on paper it is incredibly easy to construct. However, because engineered/CLT timber has not been extensively used in the construction industry yet, it’s quite hard to find architects who have worked with the material. I do expect to see an increase in residential developments depending on the project, as timber lends itself well to complex and difficult sites but as we build more in London that is expected to increase in neighbourhoods where speed of build is useful or on a difficult site, where we aim to become a better development partner with the community.
What lessons have you learned so far?
The lessons learned have been mainly from design and development process and aligning that with a traditional approach. For example, since it’s logistically processed in the factory for delivery on site, you have to ensure you don’t miss your allocated slot; if you do, you have to go to the back of the queue, which can have a massive knock-on effect on design and programme. So building with CLT is a very different process to using concrete, requiring a different kind of logic. We therefore need to educate and train the workforce how to build using CLT.
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