Delivering large and complex construction projects more often than not requires a mix of local and global engineering, material, and manufacturing expertise with complicated supply chains. During the last 18 months, the construction industry has been tested like never before in modern times following the placing of the country into its first lockdown on 23rd March 2020 and the implementation of Brexit.
Cover image: 22 Bishopsgate on the London Skyline, Image courtesy of Multiplex
As an industry we have all risen to this challenge by dusting ourselves off, investigating new ways of working, implementing the necessary infrastructure and continuing to push hard with our project teams to deliver exceptional buildings for our clients.
Regardless of the political or economic challenges, delivering complex façades in major cities requires collaboration with a diverse supply chain. As a main contractor we are responsible for understanding this supply chain and implementing it on our projects.
At our project The Broadway in Westminster the façade is nearing completion and its success has required coordination between specialist façade contractors and material specialists to deliver one of the most interesting but least obvious examples of this coordination, which is the solution to achieving the weathertightness of the façade.
The Broadway is a residential scheme delivering 250 high quality units in a prominent location neighbouring Westminster Abbey and the Houses of Parliament. The façade is constructed from a series of repeating precast concrete panels, which are highly insulated and supported from the post-tensioned concrete floor slabs. The precast panels provide two and three storey frames, which encase a prefabricated triple-glazed curtain wall. The challenge, as is often the case, lies in the interface between the two façade systems; the pre-cast concrete panels and the tripleglazed curtain wall. To achieve the architectural intent the creation of a “doughnut” precast panel with factory glazing was not possible, which means that structurally each system is independent and either supported or hung from a post-tensioned concrete floor. The typical approach to sealing a precast concrete façade is to incorporate a double seal between each panel providing robust and maintainable weathertightness.
This principle was also adopted at the interface between the precast panels and the glazed curtain walling. To improve buildability of these seals and allow robust checking on site a solution was developed to pre-install a perimeter frame around each opening. This frame was accessible from inside the building, which allowed suitable access to seal and verify the quality of each component, significantly reducing the risk of any rework. The prefabricated curtain wall could be installed into this frame using the tried and tested principles of unitised curtain wall gasket systems.
These system principles were established early in the project and developed to ensure ease of construction and maintenance. During detailed design and preconstruction the principles were built and tested off-site using a combined precast concrete and curtain walling full scale weather performance test, building the site team’s knowledge of the unique installation techniques and allowing development of a detailed quality plan prior to starting any works on site. These measures were critical in communicating the correct installation method to a team of specialist façade installers that peaked at close to 100 people during the project.
Whilst the practicalities of these interfaces were resolved and verified offsite, a greater challenge presented itself when selecting the material to seal the joints. The complexity of the support positions of the curtain wall and precast façade resulted in large differential movements between the systems, which had to be accommodated in the design of the joint together with the more usual effects of superstructure deflection and building sway. The sealant had to demonstrate excellent adhesion and compatibility with the many different materials it would come into contact with, such as powder-coated aluminium, anodised aluminium, glass, precast concrete, EPDM membranes and EPDM gaskets.
The scale of the challenge could not be underestimated, with around 55km of joints to be sealed across the six buildings on the project. A clear driver from the outset was the desire to simplify as much as possible the application of the sealant via the use of a single product. This approach would benefit future maintenance of the building as well as the construction process.
The façades at The Broadway are currently being constructed by precast concrete cladding contractors Decomo (Belgium) and Techrete (Ireland), with the curtain walling being provided by specialist façade contractor Focchi (Italy). Each contractor was responsible for understanding and designing a sealant joint for their respective works, but a deeper collaboration was required to investigate the possibility of using a sealant that could accommodate all of the building movement and material constraints whilst also being acceptable for each contractor’s stringent quality management systems. To progress a solution Multiplex engaged the expertise of Sika to review the constraints against their current product offering.
Sika found various products available that solved all of the individual issues; however, a collective solution could not immediately be found. Sika widened the search to their global markets and located a sealant formulation developed for use in the United States that had the required movement capability for the project and would likely perform well with all adhesion and compatibility requirements. A programme was put together to bring the product to the European market that involved specific staining and adhesion tests with precast concrete, adhesion and compatibility tests with EPDM gaskets and membranes, application tests, and the development of three bespoke colours for the project. In the context of a live construction project this presented a huge task against the required programme. The benefits, however, were clear and with engagement from each of the three contractors (Decomo, Techrete and Focchi) the testing programme was gradually completed and within a five-month period the product was CE-marked and certified for use in Europe.
The result has been a major success story for the project and whilst the sealant will likely be the last thing discussed when viewing the striking façade at The Broadway, the collaboration and open approach demonstrated by our supply chain has delivered a simple solution for the construction and ongoing maintenance of these buildings.
At One Nine Elms, in Vauxhall, Multiplex is constructing two high-rise residential towers and a new 173-room hotel for the Nine Elms district. The project is being delivered in partnership with Yuanda Europe who are providing unitised façades to both towers and the project’s large podium.
The unitised façades are prefabricated in the Yuanda factory and shipped to site where they can be installed safely and quickly using the tried and tested principles of a unitised curtain walling system. As with all high-rise buildings, the façades are complex and must respond to structural movements during and after construction of the towers. The particular challenge at ONE Nine Elms is an external cladding feature that is known as the “flying column,” which is suspended over two metres from the building’s concrete frame. The column repeats across each storey of the buildings, which challenges the traditional installation concept of a prefabricated curtain wall. Typically, an installation strategy would allow access safely from the floor slab with easy access to all connections and seals, but this is not possible when the column is suspended so far from the building’s structure.
In high-rise construction it is important to deliver the façade in a consistent manner, allowing each floor to be completed and made weathertight as the building progresses, which allows the interior fit-out works to progress following the same sequence. To achieve the flying column and maintain construction of the façade on a floor-by-floor basis a unique solution was required.
Multiplex and Yuanda engaged with DOKA, traditionally a manufacturer of protection screens used for the erection of high-rise concrete frames, to determine if a similar principle could be used to provide both safe access and the ability to handle a prefabricated column panel two metres away from the building’s edge. It was important that any solution used would maximise the potential for prefabrication, allowing construction to proceed quickly and efficiently whilst minimising the amount of work required at the edge of the building, which in turn reduced the amount of materials and tools needed there.
An extensive development period was undertaken, including digital modelling of the screen system and a full-scale working mock-up of the handling of a façade panel at the DOKA manufacturing facility in Austria. Typically, protection screens rise hydraulically as the building frame progresses to provide protection and access for construction operatives. In this situation, it was important that a lifting device be incorporated in the form of a monorail system that could be raised together with the screen. A separate lifting system would have increased the complication of the screen raising process, which could have put the progression of the floor-by-floor construction sequence at risk. The flying column panels, however, could simply be lifted from inside the buildings and easily moved to their installation position by the façade installers whilst suspended from the monorail.
Close collaboration was required in the planning and execution of this system and expertise was sought from the concrete frame subcontractors, temporary works designers, façade installers and screen manufacturers to provide a safe and robust solution to construct the flying columns. The result of this can currently be seen appearing to be extruded from beneath the screens on the corners of each tower at One Nine Elms.
Constructing highly complex façades in inner city locations requires a great deal of expertise and success depends upon the creation of high performing teams. It is unusual for such expertise to be held within a single organisation and it is therefore important for it to be harnessed early within a project. Often there is a complex and sometimes lengthy path to the simplest solutions requiring close collaboration between designers, main contractors, specialist contractors and material suppliers to ensure success.
This article was originally published in IGS Magazine’s Summer 2021 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Neil is Head of Façades at Multiplex where he leads a façade team who oversee a portfolio of projects predominantly in London and Scotland ensuring best practice in design and delivery of complex façades. The façade team at Multiplex is a mix of façade professionals from architectural, engineering and contracting backgrounds engaged in all projects from preconstruction to completion. Neil is responsible for ensuring the team provide technical and operational expertise to clients and projects teams across the portfolio whilst also overseeing all elements of the supply chain from specialist subcontractors to material suppliers.