Ove Arup & Partners appreciates the opportunity to respond to the inquiry on tall buildings. The company has considerable experience in dealing with issues associated with tall buildings, and believes that we are well placed to contribute to the debate in practical terms. The responses follow the format of the questions posed by the sub-committee and where Arup does not have a position, or comment, we have indicated this at the appropriate question.

  A paragraph on the initiative undertaken by Arup following the events of 11 September is also included by way of demonstrating the response by Arup in terms of understanding the implications for tall buildings and how they need to be incorporated into design and construction processes.

  Kindly note that this document is incomplete as Arup was unable to collate responses from all specialists in the time given for submission of responses. Arup will be forwarding the further comment as soon as possible and apologises for any difficulty caused.

1.  Role of Tall Buildings in achieving high densities in residential areas; the provision of offices for certain types of global companies; and as a means of enhancing the beauty of our cities

  Comment to follow as Arup was unable to generate a response given the short period of notice.

2.  The sustainability of tall buildings; in particular in terms of construction, transport and long-term flexibility of use

  The following issues are generally recognised as important features for incorporation into the planning and design of tall buildings:

—  Building Form—Shallow plan, atria or shafts allowing introduction of natural daylight and fresh air;

—  Buffer Facades—mixed-mode ventilation—summer—heat removed through wind pressure—winter—majority of heat provided through internal gains eg equipment, metabolic and lights;

—  Rainwater harvesting and greywater recycling—for toilet flushing and plant irrigation;

—  Passive Cooling—through buffer facade or chilled beam ceilings eg using cool groundwater;

—  Flexible Use of Space—ease of adaptation of internal spaces; internal green spaces;

—  Resource Use—PVs and wind-turbines;

—  Life Cycle Analysis—building for ease of dismantling to maximise material/component recyclability;

—  Infrastructure—well-served by public transport and few car-parking spaces;

—  Footprint—reduced landtake, re-use of brownfield sites;

—  Occupant Satisfaction & Health—user control, quality and diversity of work-space; and

—  Microclimate Analysis—design to prevent overshadowing and adverse wind conditions.

3.  Where tall buildings should be located, including: what restrictions, if any, should be placed on the location of tall buildings, and how far they should be allowed to block existing views; and whether they should be clustered or dotted

  The issue of clustering or dotting tall buildings throughout the landscape can be addressed in terms of the impact of tall buildings on the surrounding microclimate, particularly the modification of the wind regime at ground level. The current way of handling environmental wind issues on a project by project basis is not entirely satisfactory and is open to abuse largely through neglect. It is also essential to develop a range of urban solutions depending on the intended character of an area rather "one size fits all". There are significant risks of repeating the mistakes of the 60's and 70's, particularly since planners rarely have any formal training in environmental wind effects and how to avoid them. This is not just a problem of tall buildings but of any building which is significantly taller than its neighbours or just adjacent to an open space.

  The general windiness of an area depends primarily on the local grouping of the buildings and on the group's orientation compared to the prevailing winds. In a town or city, the apparent wind shelter that is often achieved (which is often better than in, say, a flat open park area) is a result of clustering together buildings of a similar height. Isolated buildings of whatever height usually result in levels of windiness at particular corners which are in excess of those that are felt in the middle of a flat open park. This kind of windiness may also occur around any building which is significantly taller than its neighbours. Windiness can be also be increased by creating inappropriate open spaces between buildings.

  Wind speeds increase with height above ground but once clear of the adjacent buildings, the increase with height is relatively slow. Clearly a building of greater height has potential for creating stronger ground level winds but beyond a certain height, building width is more important than height. In the wrong circumstances isolated buildings of 10 storeys or lower can create windiness that makes it potentially difficult to walk. Grouping such buildings together can make conditions better or worse depending on the details of the arrangement. On the other hand, using models in wind tunnels, it has been possible for several decades to predict windiness and guide design to achieve acceptable conditions around much taller buildings.

  We would of course all like to start with a green-field site—another Canary Wharf, where the development was carried out with full knowledge of the likely conditions in the open spaces around these buildings. In practice, in the city of London, buildings of very different sizes are built next to each other and this is likely to continue.

  As the city becomes generally taller then some current windy locations will become more sheltered and others become windier. Clearly, however, if windiness around tall buildings is to be reduced in the long term it is generally better to cluster them together giving mutual shelter rather than spread them evenly through the city. On the other hand a well placed tall building can be beneficial in clearing a local air pollution black spot. The detailed arrangement of buildings is important and the consequences of a particular arrangement should be investigated early in the planning process. It is always difficult and sometimes not practical to correct mistakes of basic building massing during the detailed design process.

  The Corbusian vision of open spaces with dotted tall towers still seems to have a grip on many imaginations. Many of the "tall" modern buildings building of the 60's and 70's were built with such uncomfortable windy spaces around the base of the buildings. There are also the visions of large buildings raised on piloti leaving grand vistas underneath—such as Stag Place and Paternoster Square both thankfully now torn down or much modified. These ideas are appropriate for climates such as parts of Italy where there is little wind and where a little wind in summer is cooling but are clearly not appropriate in our climate.

  Over recent years many developers and architects have become much more open to understanding the nature of the spaces around their buildings. This is well understood to be important to the end users of the buildings. Too frequently in recent times the main constraints in maximising good conditions are imposed by planning conditions following visions such as the above. For example, it is of doubtful benefit to the public to insist on creating urban spaces and hoping for comfortable outdoor sitting areas for drinking coffee adjacent to a tall building or in opening up such spaces under tall buildings. For regular use, such locations need to be particularly sheltered even with low-rise development. We are clearly not even as powerful as King Canute!

  It is possible to make good use of the space in and around tall buildings as long as the nature of the exposure conditions is well understood and appropriate forms of development are used. However, the solutions are often specific to the geometry of the surroundings.

4.  Whether in the present movement to erect new tall buildings we are in danger of repeating the mistakes of the 1960's

  No comment.

5.  Whether those making decisions are sufficiently accountable to the public

  The proposed changes to current practice would be:

(a)  Planning guidelines should make it clearer that the wind impact on surroundings should be properly evaluated.

(b)  Planning officers, expected to deal with tall buildings, should have formal training to brief them on the main issues of building massing that can result in poor environmental wind conditions and the things to look for in an acceptable planning submission, including when wind tunnel testing is essential and the standards that should be expected.

(c)  Wind conditions should be considered from the start of master-planning or area development studies.

(d)  It should be recognized that improvement of currently poor conditions and solution of wind problems around proposed buildings may involve developments of urban form or use of current urban forms in new ways to match the scale of the buildings. Clearly such developments should be made cautiously.

  We hesitate to increase the burden of potentially conflicting requirements on a developer—adding one more stick to beat him—but would welcome more rational ways of balancing the merits of aesthetics and the practical and economic benefits of particular developments.

6.  Whether the Government should have a more explicit policy on the subject

  The main issue associated with tall buildings is to enable appropriate area plans (including infrastructure and economic issues) to be set up, agreed and loosely costed and programmed—not to forget maintenance and updating. Traditionally in the UK this activity has been very under-resourced with a relatively narrow range of professional input. Obviously the process has to be subject to proper democratic review and local input. This clearly also involves elected representatives.

  The wider technical expertise for this in London once resided mainly within the GLC organisation. Although the boroughs may have contributed funding to it, it may still have been short of essential resources. Certainly it would only be possible to create a grouping of the appropriate skills under a London-wide (or larger) umbrella. Such a centre of expertise could also be used as a resource by those outside London although the mix of skills in the project teams would need to vary.

7.  Considerations for Tall Buildings following the events of 11 September 2001

  Immediately after 11 September, Arup assembled an Extreme Events Mitigation Task Force—a team of experts from different disciplines—to collectively assess the implications of the event for owners and occupiers of buildings, including tall buildings. This note refers to areas actively under consideration by this Task Force.

  Safety is relative, not absolute, and design standards set levels of safety based on probability and experience. An extreme event can be designed against if it can be defined, but we will never be able to define all events arising from deliberate acts of aggression. In seeking to establish what design for life-safety should mean in buildings, there is a need to embrace the idea of risk, adopting measures that are reasonable in the face of the perceived risk.

  Therefore, with reference to the Urban Affairs Sub Committee on Tall Buildings, the key aspects of the work of this task force have been to:

—  determine the design, operational and management measures that might be deployed to increase levels of safety in buildings; and

—  determine how the vulnerability of a building (relative to other buildings) with regard to natural, accidental and terrorist threats can be evaluated, as a basis for deciding which of such measures should be adopted for a particular building.

  The key areas being pursued are as below. They are generally as applicable to large-occupancy buildings as they are to tall buildings.

  1.  Evacuation and fire-fighting provision

  The existing regulations in the UK are based on principles that were developed in the 1950s. The requirements, as applied to a tall building, are based on an integrated set of measures including compartmentation within the building, fire protection to escape shafts, control of fires with sprinklers.

Evacuation requirements are based on people being able to evacuate to a protected stairwell within 2.5 to 3 minutes and evacuation in large occupancy buildings is based on phased evacuation—the fire floor and floor above being evacuated whilst other people remain on their floor. These measures have been successful—as far as we know there have been no deaths arising from fire in sprinklered office buildings in the UK since 1945.

  Following 11 September the main change in evacuation strategy envisaged is that consideration will need to be given to simultaneous evacuation—for example perhaps requiring owners to demonstrate that the entire population of the building can be evacuated within a certain period. Phased evacuation will, however, still be the safest way to handle a `normal' office fire—therefore there are implications for the management of an emergency situation.

  The work being undertaken in this area therefore deals with issues of training for all occupants, command and control lines and training for fire marshals and the like. Training and preparedness can greatly improve the chances of surviving a catastrophic event. The degree of liaison with the emergency services also is under review—and should cover such things as knowledge of the building design and the numbers of people in the building at any one time.

  2.  Design

  Improving life safety through design is always possible. The difficulty lies in the fact that if an event can be defined then it can be designed against, but without the event being defined arriving at suitable new design measures requires research. Areas under research include:

—  Structural robustness.

—  Performance of fire protection materials under different fire conditions, and under impact and blast.

—  "Hardening" of escape shafts—eg providing for blast resistance.

—  Protection of mechanical ventilation systems.

—  Public address systems and other measures to increase communication and awareness of escaping occupants.

  3.  Risk

  A comprehensive risk approach will not only consider extreme events but all types of security, natural and man-made hazards that can affect a building. Constructing a risk profile will help to determine the appropriateness of mitigation measures and importantly to assist building occupants with risk perception awareness. Work to date has been successful in providing owners with a framework for evaluating safety, and we would recommend that the Urban Affairs Sub-committee adopts a risk approach to dealing with the issue of "how safe are tall buildings?" or "how safe should tall buildings be?".

  Arup is actively involved with various bodies looking into these matters in the UK and overseas, particularly the Institution of Structural Engineers Committee on Safety in Tall Buildings, The Real Fire Research Project (London Fire Brigade), The Council of Tall Buildings and Urban Habitat, and CIBSE (providing guidance on Fire Engineering).

  Arup would be pleased to provide further briefings on any of the above issues.

  We trust that the above are constructive and contribute positively to the inquiry.