Memorandum by Lorna Walker, Ove Arup and
Partners (TAB 28)
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
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
The following issues are generally recognised
as important features for incorporation into the planning and
design of tall buildings:
Building FormShallow plan,
atria or shafts allowing introduction of natural daylight and
Buffer Facadesmixed-mode ventilationsummerheat
removed through wind pressurewintermajority of heat
provided through internal gains eg equipment, metabolic and lights;
Rainwater harvesting and greywater
recyclingfor toilet flushing and plant irrigation;
Passive Coolingthrough buffer
facade or chilled beam ceilings eg using cool groundwater;
Flexible Use of Spaceease
of adaptation of internal spaces; internal green spaces;
Resource UsePVs and wind-turbines;
Life Cycle Analysisbuilding
for ease of dismantling to maximise material/component recyclability;
by public transport and few car-parking spaces;
re-use of brownfield sites;
Occupant Satisfaction & Healthuser
control, quality and diversity of work-space; and
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
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
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 siteanother 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
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 underneathsuch
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
5. Whether those making decisions are sufficiently
accountable to the public
The proposed changes to current practice would
(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 developeradding one more
stick to beat himbut 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
programmednot 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 Forcea team of experts
from different disciplinesto 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
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
evacuationthe fire floor and floor above being evacuated
whilst other people remain on their floor. These measures have
been successfulas far as we know there have been no deaths
arising from fire in sprinklered office buildings in the UK since
Following 11 September the main change in evacuation
strategy envisaged is that consideration will need to be given
to simultaneous evacuationfor 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 firetherefore
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 reviewand should cover such things as knowledge
of the building design and the numbers of people in the building
at any one time.
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:
Performance of fire protection materials
under different fire conditions, and under impact and blast.
"Hardening" of escape shaftseg
providing for blast resistance.
Protection of mechanical ventilation
Public address systems and other
measures to increase communication and awareness of escaping occupants.
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.