WorkStack, Charlton

WorkStack, in Charlton London, takes advantage of the benefits of both structural timber and offsite construction. The ingenious solution optimises land usage on a compact and restricted urban plot by adopting overlapping, cantilevering workspaces, which progressively increase in floor area to create 14 new industrial units scaling in size from 55m2 to 110m2. Manufactured offsite to achieve both speed and accuracy, Cross Laminated Timber (CLT), with its high strength to weight ratio, was the ideal material to facilitate this unique and optimised inverted form. The end client Greenwich Enterprise Board (GEB) – a social enterprise with over 20 years’ experience of developing affordable workspaces – assembled an expert project team for WorkStack. Architecture practice dRMM was selected to head the design team while ARUP acted as structural engineer and fire strategy consultant. F Parkinson was appointed as the main contractor, with B&K Structures selected as the specialist subcontractor responsible for the CLT and steelwork package. This included the steel connection design to enable the construction of this innovative, cantilevering five-storey structure.

Design

From the concept stage, the project team sought to overcome multiple technical challenges linked to WorkStack’s unusual form, as well as its location on a busy road with limited room for storage. Early engagement and collaboration by the entire team was fundamental to the project’s successful design and construction. Among the first challenges of the project was the building’s unconventional form and groundbreaking design, which included CLT panels with much larger spans than standard to form the walls, roof and floor slabs. The panels were up to 19.2m in length compared to the more typical length of 16m, which meant that the design sat outside of the existing available test data and required a collaboratively developed bespoke solution. 

Fire safety was a priority from the outset. As the timber elements were intended to remain exposed when completed, there was a need to develop fire safety solutions that would not detract from the visual impact, while still achieving the required fire resistance. As a trailblazer in innovative fire safety design, ARUP collaborated with Building Control and the London Fire Brigade to configure each workspace as a separate fire compartment, augmented by smoke extract and other mitigations. This addressed shortcomings in existing standards with respect to the use of mass timber in major buildings. ARUP also worked closely with BKS to design a mixture of  standard and bespoke solutions that concealed the steel plates and screws, while prioritising compartmentation and avoiding the need for fire resistant plasterboard linings.Simon Bateman, Senior Structural Engineer at ARUP, said: “The design included a bespoke smoke ventilation system and stringent fire safety performance criteria for the CLT panels, including the systems that need to interface with the CLT panels, such as fire doors, fire dampers and encapsulation.”

To achieve this ambitious design, BKS’ supply chain partner, Stora Enso, utilised a highly digitised Design for Manufacture and Assembly (DfMA) approach. This enabled clash detection as well as material optimisation, by augmenting individual panel sizes to reduce waste offcuts in the factory to just 2%, all of which was later recycled into biomass pellets. 

Construction

The benefits of an offsite timber solution played a significant role in the success of the project. Specifying offsite manufactured CLT and supporting structural steelwork for WorkStack allowed much of the work to be completed to a high degree of accuracy in the factory. The quality of the panels during manufacturing was ensured via checks at nine different points along the process through to final loading inspections, with photographs taken of departing loads. As part of ISO9001, the glue line of the CLT panels was reviewed with laboratory tests 20 times per day, as well as checks for delamination conducted five times per shift. The offsite delivery model reduced the build phase on site by 25%, lowered onsite waste, and provided cost certainty compared to using traditional construction methods. With much of the work completed offsite, effective design clash identification and accurate installation planning, the structural elements of the project were completed on site by BKS in just eight weeks.

During the onsite phase of the project, BKS continually reinforced best practice. This included rigorous implementation of CDM regulations, from the design stage to drawing up a thorough risk assessment. BKS also conducted weekly toolbox talks, covering topics ranging from working at height to moisture protection for the varied CLT elements. Key aspects included end grain protection and the early plugging of WorkStack’s 30,000+ screwed connections, as well as special emphasis on achieving compartmentation for fire performance.A key benefit throughout the construction stage was F Parkinson’s meticulous care of the timber, including applying protection to the corners of the CLT at openings which had heavy foot traffic. 

Additionally, exposed timber is often used by follow on trades as a surface area to make notes and calculations. As each new trade came on site and commenced works in areas where CLT had been installed, F Parkinson made these trades aware that the exposed timber was a finished surface and would not be covered up, to maintain the final visual appearance. F Parkinson’s Site Manager, Peter Evans, commented: “While F Parkinson as a company had previously completed three or four engineered timber projects, Charlton WorkStack was my first timber experience as an individual. The management of the installation and the standard of the workmanship was A*. 

Personally, carrying out the onsite inspections highlighted the standard of the prefabricated elements – there were no defects when we came to handover the project, and the speed with which the structure went up was unbelievable. Built during covid restrictions when travel was limited, very detailed information sharing was vital. As well as ARUP’s involvement as the fire consultant, we got London Building Control in at regular intervals to inspect each stage as the build progressed.Finally, as well as the installation of fire-stopping materials, the fixing details were quite robust, with screws at 50mm centres in many places. From our learned experience on this project, I wouldn’t hesitate to work on another timber project with BKS again”.

Sustainability

WorkStack achieved high levels of energy efficiency and sustainability, with the completed project including 21% less upfront embodied carbon than the Low Energy Transformation Initiative’s (LETI) 2030 Design Target (of 350 kgCO2 /m²), and 44% less than The Royal Institute of British Architects’ (RIBA) 2030 Built Target for whole life carbon (of 750 kgCO2 /m²). The use of structural timber made significant contributions to lowering the embodied carbon thanks to the material’s natural ability to capture carbon as the trees grow. WorkStack’s 705m3 of CLT walls and floors, and 4m3 of glulam sequester 532 tonnes of carbon while emitting only 10% of this during manufacturing and transport (53.2 tonnes CO2e). With full PEFC chain of custody certification, the responsible management of the European forests by BKS’ supply chain ensures that the timber for the project will have regrown in just 66 seconds.

In addition, the demountability potential offered by the use of structural timber contributes to the circular economy, further enhancing the project’s sustainability credentials. In term of energy efficiency, the design of the building included a number of passive energy efficiency measures. For example, the cantilevered form provides solar shading to the west, while the sizes and location of openings ensure crossflow ventilation. Careful coordination across the project team during construction ensured a tightly sealed building. The development also features an air source heat pump to generate renewable energy. Overall, the result is a sustainable project which is on track to be rated BREEAM Excellent.

Conclusion

As an urban workspace, WorkStack offers affordability, flexibility and excellent transport links. The 14 new units are ideal spaces to allow new creative enterprises to grow, and the project breaks the mould 
of ubiquitous ‘tin-shack’ industrial units. With the industrial sector emerging as a growing market for engineered timber and hybrid construction, the delivery of WorkStack as a light-industrial building is a great example of what can be achieved with structural timber.  

Awards

 • Best use of Timber Technology -  Offsite Awards 2024
 • Solid Wood Project of the Year -  Structural Timber Awards 2024
 • Architect of the Year (dRMM) -  Structural Timber Awards 2024
 • Commercial and Leisure (Winner) -  Wood Awards 2024
 • Structural Category (Highly Commended) -  Wood Awards 2024