Design flexibility can allow a building to evolve over time as the user needs change. The flexibility of a building or elements of its design can allow it to be used efficiently despite changes in operational requirements, whereas an inflexible building might become obsolete.
Flexibility might include active flexibility, such as moveable partitions, but can also include the provision of features that are inherently flexible, such as multi-use spaces, open plan offices, large floor-to-ceiling heights and high-capacity service voids. It might also include broader characteristics such as a room’s ability to expand or to use a range of different energy sources, deconstructability, and so on. This can include consideration of very fundamental design options; for example, it might be relatively straight forward to make a linear building larger or smaller by adding or removing a bay, whereas a circular building may be very difficult to change without affecting the integrity of the design.
However, there are many buildings with very expensive designed-in flexibility that is never used, as the requirement for change never emerges, building occupants are intransigent and avoid change, or occupants may simply be unaware of the possibility to of change.
 Types of flexibility
Flexibility can be defined within three broad types, relating to the amount of change which occurs and the degree of permanence of that change.
This is the capacity of a building to support multiple functions without altering the architecture itself. In simple terms, the function of the building changes but the building does not. Examples include furniture that can be re-positioned, multi-function spaces and so on. These do not result in a permanent change to the space.
This allows for the interior or exterior space to be changed in response to certain stimuli without the need for new construction. Changes can be both permanent and temporary.
There are two sub-sets of transformability:
Moveable structures can be repositioned within the environment without being changed or altered in any major way. Examples might include moveable fabric structures, re-locatable retail units, temporary accommodation such as site huts, portaloos and so on.
Responsive structures are able to react to external stimuli such as weather conditions. The changes are often temporary, but may be resource-intensive. Examples include floating buildings that rise and fall with changes in water level, retractable roofs over sports facilities and so on.
This involves changing the function of a building through a certain amount of construction work. By planning for convertibility during the design stage, potential future needs can be assessed and the time and cost required can be reduced. The resulting changes are often permanent. This might include for example; allowing sufficient space for additional buildings, providing foundations for future expansion, over-sizing building services to allow for future expansion, or conversely, purchasing packaged building services that it might be possible to re-sell if requirements reduce.
 Designing for flexibility
The incorporation of any anticipated flexibility into the design of a building should take place early in the planning phase of a project. The earlier that decisions are made, the easier the implementation and the greater the potential benefit. As a project develops, it can become increasingly difficult to incorporate strategies for flexibility.
In the planning phase, initial feasibility studies, future projections and long-term plans should be used to inform the development of flexibility strategies. If the project has end-users who are known, it is vital to consult with them as a means of identifying the forms of flexibility would be most beneficial to them.
Once flexibility objectives have been determined, the design team can review potential strategies and evaluate them based on their suitability for the project, bearing in mind the site constraints, programming requirements, available budget, and so on. A cost benefit analysis can help determine whether providing flexibility is actually in the long-term interests of the client or whether it is an unnecessary expense, the benefit of which is unlikely to be utilised. No designs can take accommodate every possible future requirement, so the design team must carefully evaluate those that likely to be the most beneficial and the least disruptive.
 Flexibility during design and construction
Fast track projects may involve the overlapping of activities in order to deliver a project more quickly than it would be by traditional methods. This can include overlapping design and construction, that is, construction may begin before the design is complete.
In this case it may be necessary to provide some flexibility in the earlier stages of the design to accommodate more possible options later. For example, foundations may be constructed before the form of the above ground building has been finalised. This may require that building foundations extend beyond the shape that will actually be required, and allow for greater structural loads than will necessarily be needed when the design is complete.
It may also be necessary to order some long lead time items before they have been fully specified, and again this can result in over-sizing to allow flexibility. This might for example affect the sizing of building services, construction plant and so on.
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