• Ed Moseley

THE BEST TIME FOR REFURBISHMENT IS NOW




London Structures Lab reviews the recent redevelopments that are achieving significant savings and design accolades across London. With the recent Architects Declare and Engineers Declare statements both pushing the agenda for re-use there is now a petition in front of the House of Commons pushing for tax relief for building re-use.


“Upgrade existing buildings for extended use as a more carbon efficient alternative to demolition and new build whenever there is a viable choice.”

From both the Architects and the Structural Engineers Declare Climate and Biodiversity Emergency


The time is now

There has never been a time where redevelopment and rejuvenation of London’s stock has more appeal than now. Whilst the idea of refurbishment is not new, recent political and technical developments mean that developers are driving more value from the use of old buildings than ever before. Planning authorities are increasingly favouring the re-use of old building stock to help preserve London’s architectural heritage and deliver carbon savings. Innovative re-design is breathing new life into an old buildings, enriching their character and strengthening the planning story, whilst delivering value for the owner.


The GLA carbon tax, brought in at the end of 2016, is one of the new stimuli for re-using old building stock. Since 2016, the more carbon you use, the higher the environmental impact and the higher the levy. Richard Twinn, Policy Advisor at the UK Green Building Council, warned many developers are still in the dark. “It’s going to require architects to go further than they have before”. “Developers will be looking for things that can be done on site to help them minimise their offsetting costs. They will have to go further than they ever needed to before or their schemes will be turned down.” Here at LSL we have identified that retention of the embodied carbon in existing structures can save hundreds of thousands in tax on some of the projects currently under construction.


Refurbishment of old stock has always been part of London’s development scene. But what makes it so exciting right now is the development of new computational tools to generate significant increases in area without the need for additional foundations or vertical structure.

The modern office

London has an extensive stock of commercial buildings built between the late 1960s and early 1980s. Changes in architectural styles and building performance have meant an evolution in the way an office functions and how it is expected to perform. Commercial buildings from this period are now dated in terms of architecture and functionality. Whilst these assets may not show the same potential as new assets for let–ability, they are prime stock for structural reinventions.


Construction during the 1960s-80s pre-dates the computer revolution and buildings from this era can exhibit extensive structural redundancy due to rationalisation and standardisation of design. In addition, many structures were developed for what was believed to be the future of commerce. Floor capacities were designed to carry large computers or semi-industrial equipment, or at the very least heavy paper lead office systems.


Through study of the existing structural drawings, many of which were well recorded during this period, it is possible to identify potential for expansion and reinvention of this building stock in an economical and sustainable approach to London’s built environment.


These benefits can only be fully realised by early engagement with the design team by a client who is willing to invest in research and study of the building’s potential prior to going to planning.


Space gains and cost savings

The re-development of Southbank Tower is an impressive example of the benefits that can be realised, designed by KPF architects and AKT II structural and civil engineers.


South Bank Tower – completed in 2016

South Bank Tower is the re-invention of the Kings Reach Tower built near Blackfriars Bridge in 1972. The existing building consisted of a 31 storey office tower and a 6 storey office podium building both of which were concrete construction. The redevelopment added more than 50% to the area of the site which was realised as additional residential area, the office area being required to be maintained as a planning constraint.


The project benefited from several aspects of the original design – a high original design load, a change in use from office to residential, an expressed and rationalised structural form and a core designed for the original vertical transportation technologies, which was of its time.


These original design features enabled an additional eleven stories to be added to the tower and an additional three stories to be added to the podium building. Whilst extensive modifications were carried out to improve the building’s functionality.

The structural analysis approach undertaken for the project to identify potential for reinvention of the existing structure is broken down by key elements below to help inform potential assessments of other developments. Here at London Structures Lab we have tried to show how these key considerations can be applied to an initial assessment of an existing building, as a guide to those looking to invest:


Foundations


The foundations for the Southbank Tower are primarily under reamed piles. This was a structural approach in the early 70s and includes a long pile shaft with a concrete bulb at the base. This means the foundations rely on end bearing of the pile rather than skin friction along the shaft length. Over time, London clay subject to this bearing will change its pore pressures resulting in an enhanced ground bearing capacity. This process may take up to 60 years to be fully realised but even after 45 years a potential 40 to 50% increase of the capacity of the foundations can be possible.


Columns

The types of columns for the buildings of this period were frequently heavily rationalised (simplified structural analysis) for construction efficiency and designed for higher imposed loadings. Modern BCO guidance has moved away from heavy floor loadings to match the emerging office trends for lightweight tech and paper free environments. Utilising this extra design capacity and finding the redundancy in the structure due to the more advanced analytical approaches available today gives opportunity for extension and expansion of structures without the need to enhance the existing column arrangement. In the case of South Bank Tower, the expressed concrete frame had been developed as part of the architectural concept, and had columns at significantly closer spacing’s than required for structural performance.


Cores


A building’s core size can be defined by many factors. In older buildings, stabilising the structure can often be a secondary influence compared to vertical transportation and building services distributions. Concrete shafts were larger than those of modern buildings due to larger lift sizes in the 60s and 70s.These drivers for core size resulted in redundant capacity within the structural system. This coupled with more advanced understanding of wind behaviour and the behaviour of tall buildings has resulted in opportunities for the extension of structures whilst avoiding the need to enhance cause beyond their original design.


In the Southbank Tower, wind analysis reduced the design wind loadings to less than 80% of the original loadings. Detailed analysis of the core facilitated the demolition of about 30% of the concrete walls between levels 11 and 30, enabling the utilisation of the core to be maximised and creating the additional doors required for the change of use from office to residential.


Floors

As with column assessments, floor structures were frequently designed for higher imposed loadings than is considered to be required for modern building design. This enables modifications to be made to existing floor plates as long as the original design parameters are considered.


It is important to note that fire regulations have changed regulations have changed significantly since the 70s and 80s. Structures were not previously assessed for their durability in the event of a fire. Understanding a building’s ability to withstand the current design fireloads is an important factor in assessing its reusability.


Whilst choosing to re-develop or design existing stock requires commitment and determination from developers and architects, there is no doubt that the sizeable benefits can outweigh any investment into viability the pre-planning phase. In the high-pressured world of inner city developments, high quality re-developments can get a building back a year earlier, deliver substantial savings and attract the approval of planners and environmentalists.


Developers and investors who have existing stock and who are considering the potential for re-development should consider an analysis of the infrastructure to reveal its full potential. Those looking to purchase a new building should consider their ability to offer a competitive price through adding additional area, functionality and value through an innovative re-design.


For more details or advice on any potential re-development contact us here at London Structures Lab.