MAKING STRUCTURE PART OF THE CITY'S INFRASTRUCTURE
Making structure part of the city’s infrastructure
Against ever increasing calls for sustainability in our built environment, commercial buildings continue to be built, demolished then redeveloped. This can occur over a surprisingly short time scale. A previous London Structures Lab article (https://www.londonstructureslab.com/post/7-steps-to-minimising-material-usage) has looked at stopping this cycle through re-use. Here, we will explore opportunities for improved longevity in new building stock through the use of considered design strategies.
The cycle of development is driven by the increased densification of the city, land-owners looking to gain further value out of sites and the practice of deeming buildings not fit-for-purpose. Fit-for-purpose is determined by whether the building meets ever-increasing specifications, changing market trends and occupiers’ needs.
The wasteful demolition of building structure has to stop. We cannot keep designing buildings that will be ripped down in 30 years or less. Given what we know of the impact of the construction industry on climate change, it would be irresponsible to keep doing so.
Changing market trends
New companies operating in existing markets and those in emerging industries have different requirements of their buildings from their predecessors. Tech companies and co-working providers are highlighting the possibilities of different ways of using space. There is also an ever-growing body of research into how space planning can increase occupiers’ happiness and productivity. Their space requirements focus on diverse space utilisation, ranging from large volume collaboration areas to small focus work areas and spaces that require higher specification such as formal presentation venues and kitchens.
The average age of a company has also significantly reduced over the last 60 years, with the S&P 500 average company age dropping from 61 years in 1958 to 18 years in 2017[i]. Alongside this, average lease lengths have also fallen, reaching a low of 4.7 years in 2010[ii], although this has now risen to 7 years. These trends have led to greater demand for changes to existing building stock. Given the historical data and trends, it is impossible to state that what we build now will meet the needs of future users. And as Stuart Brand said: All buildings are predictions. All predictions are wrong. There's no escape from this grim syllogism, but it can be softened.
Given that commercial demands for space will continue to change, there are two approaches that can be explored to help break the current cycle of demolition – resilience and adaptability. As you explore these paths, it emerges that they are not necessarily distinct but points along the same range. If we are to rebuild, we need to do it well and aim for permanence. The goal should be for the structure to become part of the city’s infrastructure. These structural frames can then be occupied.
The Resilient Building
The resilient building is one that can be reworked by different occupiers without major modification. In many resilient buildings, the base materials are robust and there is little that is superfluous. To maximise flexibility of use, an accepted approach is to pare the building back to common denominators. The fit-outs must then make up for the shortfall to meet occupiers’ needs or any required specialisation, but the degree to which that can be done is limited to an extent by the fabric. As the approach is to minimise reworking of a building and the design must accommodate the possibility of many uses at once, there are inevitably some compromises on the building’s ability to fit all types of occupier. A choice is then made by the developer and design team as to whether they want to fit a wide market adequately or a more focused market well.
Traditional London warehouses were built as open plan floors unlike most other buildings of their time, which means an array of columns rather than load bearing walls. They can also have deep floor plans which suits the current fashion for open plan working, with natural light seen as less of a priority. Converted warehouses are often sighted as exemplar case studies of resilient buildings. But almost all older structures that have been reused over the years are resilient. Factors that make these buildings more likely to survive are if there has been a degree of over design, for example high loading allowances or high ceilings, if it has been well maintained and has avoided even a short period of obsolescence or if there is a high design quality which gives the building some additional value.
With converted warehouses, there are arguably other compromises made by the occupiers in these buildings, but this is justified by the character they offer and traditionally cheaper rents. There have been several buildings that have aimed to offer the modern version of this and some very successfully drawing on the warehouse principles directly, such as AHMM’s White Collar Factory. Due to the prediction of possible future uses, a degree of overdesign is often added. This can be in many areas, including loading allowances, floor to ceiling heights and servicing strategy. If these buildings occupants utilise these allowances in the future and it results in an extension of the building’s life, then in sustainability terms these are good solutions. Exactly equating the additional embodied carbon to extending structural lifespans is challenging, but if a building’s structure can survive the life cycle of refurbishment for even one extra cycle, then a few percent additional carbon in the base build is easily justified.
Whilst resilient buildings are a perfectly sound approach care has to be taken to not over specify, identify how much the shortfall will be between base-build and fit-out to the optimum occupier needs and not to fix in a design aspect which is prone to change.
The Adaptive Building
The adaptive building allows the structural fabric to be adjusted to the needs of the occupier, enabling a tighter fit to their optimum arrangement. A basic, but common example of this would be the traditional soft-spot for a stair linking two floor levels, which can encourage connection between parts of a business or access to amenities. These soft-spots have traditionally been made in the same construction as the rest of the floor plate, with the area being broken out and structural material disposed of.
Often reinstatement of this structure was not even considered by the base build, no doubt because leases were typically long enough for it not to be the landlords’ concern. A true soft spot should be easily deconstructed and reinstated using reusable components. This can mean using mechanical and reversible fixings such as bolts and screws, rather than chemical bonding such as concrete and glues. Morris and Company used such a solution on their Kings Cross R7 project, where the concrete slab had a steel trim at the perimeter of the soft-spot. This trim has bolt holes that can either take a handrail or joists for a lightweight infill. All components can be lifted using the building maintenance Davit System and stored until required again.
Kings Cross R7 during construction - courtesy of Morris + Company
Another very common example can be found in retail where double height units are designed to allow for a mezzanine floor. The various considerations are worked through for the space in both the double height and infilled configuration, but the floor is put into the retailer’s fitout. This level of tenant fitout is not seen in offices yet which could be for several reasons. One factor is that more analysis is carried out by retailers to determine the optimum configuration for their sales. This data combined with the higher rent and potential returns on the space, mean there is more impetus to make significant changes if required. Retailers also spend more on fitout, do it more often and commonly have multiple locations, so they have the knowledge and expertise required that most office tenant organisations do not.
Currently, new build offices with central atria commonly have the structure to the perimeter of the void designed to take link bridges or to be infilled completely. This means enhancing the beams/slabs, columns and foundations. This potential additional floor area cannot be realised if the lifting and servicing is not also enhanced in the base-build or enabled for modification. Developers should therefore consider adaptive planning for all inter-connected elements. Only a holistic approach will allow any potential to be realised.
As workplace research increasingly demonstrates the value of design on productivity, it would be expected that tenants start to develop a greater understanding of what suits their teams. The ability to offer tenants something that can be brought closer to those needs is likely to give a landlord an advantage in attracting tenants and with this greater occupancy and higher rents.
This greater range of options should mean it is less likely to be demolished. But it requires elements of the building to be enhanced or over designed in a similar way to a resilient building. To ensure the client, occupier and the environment can get the return on this investment, the design team must consider multiple configurations during the design development.
We know that London is set to continue to grow as are many cities. As this happens, they will have to become denser, which in itself has some sustainability advantages. In adaptability terms, this means further changing the massing of buildings in the future and we must aim to do this without demolition. Adding additional floors to buildings can easily be allowed for in the vertical structure and foundations with minimal additional cost. Though this, like a resilient building would be through over-design and will only be efficient if the capacity is eventually used.
What really limits the delivery of these extensions with the current building stock, is the arrangement and construction of the cores to allow for the increase in both the lift capacity and the quantum of services. This can be done through leaving soft-spots if the core if central or putting lifts on the perimeter and leaving enough space to add later. It also needs careful planning of the core in the two configurations so that items are not landlocked or required to be moved to allow for the changes.
There is no real limit to the extent of a building that can be made flexible and the recording of information for future design teams is now standard practice. But as this is in effect moving part of the structure into the fitout of a space. It means a greater amount of material can be altered during a refurbishment and that risks there being more waste and embodied carbon produced. Further to the above reusability, the notion of ‘buildings as a material bank’ https://www.bamb2020.eu can be a useful approach to minimise the lifecycle impact.
Combining resilient and adaptive approaches
As you analyse an adaptive building it becomes apparent that the structure splits into two parts, that which can be altered and that which should not. The area that does not change can be approached as a resilient structure and the adaptable portion as larger and larger parts of the building’s fitout. In all the design decisions, we cannot be sure what the future use will be, but we can try to predict the options and curate the elements, so that we can accommodate the required changes with as little waste as possible and minimum lifecycle impact.
To help stop the cycle of demolishing buildings we need to look at how we can make them work for us in perpetuity. Sewerage systems and electricity grids are installed with additional capacity to support cities as they grow. As limits are approached, demand is adjusted. When the limit is are finally reached the system is supplemented. It is possible to see structures in a similar way - as fixed yet perennially changing elements of a city’s infrastructure. When we begin to view buildings in this way, a multitude of likely future scenarios will need to be considered. The tighter we are able to get to understanding these scenarios the less redundancy will need to be built in. The design team and client will then need to decide the degree to which they will allow for compromises in the solutions and use this analysis to decide where along the resilient and adaptive scale they want to place their building.
To end on another Stewart Brand quote, ‘a building is not something we finish, but something we start’.