Early specialist support crucial for tall buildings
The early involvement of specialist contractors will be increasingly important to the successful design, delivery and operation of tall buildings, says BESA technical director Tim Rook.
The direction of construction in this country is up. We are building faster, denser and higher — yet most tall buildings are approached as ‘bespoke’ projects with no standard approach to their design, construction and operation. With over 200 new high-rise buildings planned for London alone, it is clear that a unified set of guidelines for the supply chain is urgently needed.
Most high rise structures are mixed use — residential; retail; commercial office; leisure etc. — all of which can change radically during the building’s operating life. The design process can also last for many years and is, therefore, at the mercy of significant economic, political and social changes that can radically alter the developer’s vision for the building part way through construction.
All of this creates a unique set of challenges for the technical trades given the task of designing, installing, commissioning and operating the services.
Today’s tall buildings are more like vertical cities with a wide variety of occupants and rapid changes of use. The design team also has to be thinking extremely long-term — 80, 90, 100 years. What services will future generations of occupants need, and how will technology alter how they are delivered? Will they need a car park for all-electric, driverless cars? Will there be cars at all?
Even post-occupancy warranty issues need to be considered early because these can be extremely complex to satisfy multiple tenants, all with different requirements. The project team has to be aware of the type of warranties that will be given at the end — even if the handover process is many years in the future.
At the Building Engineering Services Association (BESA), we have been working on these questions for some time. We have launched an interactive ‘wiki’ to gather expert data and recently hosted a supply-chain forum comprising architects, consultants, contractors, builders and legal specialists all with particular expertise in tall buildings.
In a full-day interactive session, the BESA forum looked at how tall-building supply chains currently operate and where this is creating weaknesses in delivery and long-term operation. The members considered the implications for the surrounding area and the local community and how a tall building becomes a catalyst for other projects and other spaces.
The definition of ‘tall’ covers any building where, because of its height, there are specific engineering challenges, changes and additional considerations that go beyond normal practice in order to ensure a safe and efficient system.
Therefore, the forum members looked at how the specific challenges created by tall structures impacted on the design and safety of pressure systems, pipework and jointing selection, anchoring and expansion, fire systems (sprinklers, dry risers), large VRF air-conditioning systems, cold water services and many more.
Over 20% of the total construction costs are down to M&E services, according to the consultants Davis Langdon. Yet specialist contractors with crucial knowledge of these services are usually left out of the process until the later stages — a fact that the whole forum agreed was hampering project delivery and undermining ongoing operation of the completed building.
With multiple types of occupant, the arrangement of the services is a ‘day-one issue’, with an early decision made about the position and nature of the services ‘core’ critical to the overall design. Similarly, construction logistics need to be considered from the outset as most tall buildings are in tight urban areas — creating serious access issues, particularly with the amount and size of equipment to be transported in.
It was recognised by the forum that a great deal of value can be brought to the table by the contractors who will carry out the work and that it would be preferable to do this early in the design process. There was even a willingness to consider making this a paid-for service.
Some developers do bring in specialist contractors at design stages 2 and 3, which can be as much as five years before work starts on site in a complex tall building. However, in most cases the specialists are brought in after construction has begun — and that is too late.
Architect Simon Bowden told the BESA forum that lifetime design should be a priority right from the concept design — with the architect, client and developer being clear about how long they expected the building to operate.
He said, ‘You must make the building flexible enough to deal with changes in use — particularly in the office space. You need to look at the floor plate; it is wrong that so many offices are demolished when they should have been designed for re-use with a longer design life built in.’
WSP Parsons Brinkerhoff technical director Peter Brickell said ‘everything depends on the core’.
“If you are building for residential then you need the core in the centre to maximise living space around the perimeter, but offices often have different requirements, with a deep floor space and only senior management out on the edge of the floorplan,’ said Mr Brickell.
He said that a floor plate of approximately 18 m was a good rule of thumb because it works for residential, hotels and offices — and can be adapted later depending whether the core is in the centre or not. He added that the design team should look to ‘blur the lines between office and residential so you can change in future, aiming for spaces that could suit both, with floor-to-floor heights of around 4 m.
‘If the cores are at the edge, you can keep the integrity of the floor plate when making changes.’
However, this means that heating and cooling loads must be discussed at the outset because every occupant will have their own particular needs and targets, which have a ‘profound impact on the design of the core and, by implication, the footprint’, according to Valeria Khnykina of SSE.
‘One of the first decisions should be the position and size of plant — basement/mid-level/rooftop,’ she added. ‘If you have chiller plant on the roof, that has major structural implications. And if you have a hotel in there, will it want its own services arrangement because of its different usage patterns to the offices etc.?’
If the building is to be connected to a district-heating supply that also has to be designed early so you need to know what the loads will be — particularly if you want an efficient ∆T (hot water supplied at 90 to 105°C, with the return at 30 to 40°C). So, will there be a requirement for buffer vessels or thermal stores?
The forum also discussed the role of lower-temperature systems as a result of increasing use of heat pumps and the difficulty that could create in getting the right balance of temperatures across the whole structure.
Early input from the FM team is essential to ensure good management of the technology throughout the building’s operating life. BESA vice president Giuseppe Borgese said that core services should be done in such a way ‘so that you don’t need to shut down the whole building when replacing or refurbishing’, but that often requires FM specialists to make themselves unpopular by asking awkward questions of the designers.
From a construction point of view, ‘Verticality is really important,’ said Kevin Mason of Briggs. ‘In lots of projects, the services are removed from the core and that creates real problems. If you have toilets at every level, then you have waste pipes coming through in various places and that can have a big impact on your flexibility.’
He said manufacturers were producing more modular equipment and offsite fabrication was improving. ‘However, they could put more thought into how it is ultimately going to be assembled on site. For example, do the pieces of plant have to be so big? Or can you give us boxes that can be taken apart and reassembled on site to ease access and lifting issues?’
He also stressed the importance of managing operating pressures in tall buildings and techniques for avoiding the need for interstitial plant rooms as these add cost and complexity while also taking up valuable space.
Advances in mobile technology mean the integration of smart systems and how they are going to control the services is another early consideration, according to Tom Smith, global director at WSP Parsons Brinkerhoff. He said this also had long-term implications for the health and well-being of occupants.
This is an increasingly important consideration for clients that goes beyond obvious issues like indoor air quality to how people are being encouraged to use the stairs more often than the lift, for example, as part of the WELL Building Standard, which is now being adopted in many countries.
The BESA tall-buildings forum is continuing its work to develop industry standard guidance, which will be developed and published on a sub-topic by sub-topic basis via its ‘wiki’. Adopting this dynamic, online approach will enable the working group to readily update its content with strong links between sub-topic publications and make access easier for members.
For further information or to join the wiki task please email: mark.oakes@theBESA.com.