by Greg Wilson and Roger Norton
The past few years have seen a steady increase in the number of tall buildings proposed in our urban areas, particularly in London. It is inevitable that this demand will continue, fuelled by economic and technological factors, as well as by the desire by some developers and their clients to erect tall buildings as an indication of their prestige and as a statement of their corporate identity. With the current debate about the appropriateness of tall buildings in certain locations, it is perhaps timely to review the means of preparing and presenting a proposal for a tall building to a planning authority.
For the purposes of this article we shall assume that a tall building is as defined by the Greater London Development Plan in 1976: “A high building is one which significantly exceeds the height of its surroundings and includes all types of structures such as masts, pylons, cooling towers, chimneys . . . .”
The design and location of tall buildings is critical, since their visual impact goes far beyond their immediate surroundings — hence the importance for would-be developers of presenting their proposals more clearly, applying existing techniques. These techniques enable developers to fine-tune their designs and to achieve the best relationship between the proposed building and its surroundings. In addition, they enable the planning authorities and other interested parties to be clearly informed as to the implications of the tall building proposal. There are a number of actions that should become standard good practice in accompanying planning applications which are discussed below.
Liaison with the local planning authority
It is important that developers’ consultants test the proposal against any relevant advice and policies, especially the local planning authority’s planning policies. Approaching the local planning authority early in the design of the scheme to test its reactions to the proposals is beneficial, as the authority is understandably keen to provide advice and comments on the proposals as they are developed. Its confidence in the proposals, although no guarantee of a smooth passage through the planning application stage, is always useful. Providing evidence of the visual impact which a tall building will make not only helps the developers’ consultants to make their case but will also assist the local authority planners.
Visual impact
One way to see how much of the building will be visible is to tether a balloon corresponding to the height of the building. This simple method can be used on its own to verify the findings of any other visibility study and it will also give a general impression of the overall size of a building as perceived in its setting. This method has been used in a number of situations and, if nothing else, is a realistic presentation of the likely impact of a tall building. However, it is of limited use in densely developed areas and requires calm weather conditions: a more reliable method is to erect a crane to the appropriate height.
Plotting the visual intrusion of a tall building is possible with an intervisibility study. Taking a contour map with the heights of any significant features marked on it and with the tall building centrally located, a number of sections should be produced; the more sections, the more accurate the study. It is possible to carry this out for an urban or rural area, although many more sections will be required for a built-up area because of the greater number of height variations. The sight lines are plotted on each section; these are transposed back on to the map and it is then possible to plot on the map areas where the tall building is wholly or partly visible or not in view.
3D modelling
Recently our practice was involved, as masterplanner and architect, in the preparation of a detailed planning application to Westminster City Council for a 22-storey building as part of a mixed-use scheme at Paddington Basin. Regular consultations were held with Westminster council as the designs progressed and its comments were found to be most helpful, enabling certain modifications to be made. We prepared plans, elevations, sections, perspectives and a model. In addition, photomontages of the proposals were prepared along with comprehensive computer modelling of the scheme’s many different elements — housing, offices, hotel, shops and leisure facilities. Modelling in 3D by computer has matured over the past few years. It has always been feasible and accurate, but it has recently become much simpler and generating images from the model has become quite sophisticated. Computer-generated scenes are now so realistic that they are universally accepted in the television and entertainment industries. Architecture looks set to follow suit.
Once an object and its surroundings have been modelled, a computer system can perform a number of functions. In a building context the computer is able to:
- generate views from any eye position in any direction (this is essential to provide visual impact analysis and massing studies);
- generate shadows cast by the proposed development (other rights of light and party wall infringements can be studied in this way);
- compute accurate site and floor areas, as well as building volume;
- generate views for phasing studies (this is particularly useful in predicting the visual effect of demolition on the aesthetics of the environment;)
- simulate wind conditions to help predict problems at pedestrian level;
- create animations, where many views are generated in sequence to simulate movement through or past the proposed development;
- produce photomontages, where computer-generated images of a proposed development are set in actual images of the site and its surroundings
A photomontage is an accurate perspective of the proposed development set in a photograph of its environment. This is a telling contribution to any presentation and is increasingly used. We have also provided computer-generated photomontages for public inquiries, using our own computer system, Acropolis, to create well-modelled schemes which include buildings, trees, people and landscape features.
In order to create an accurate photomontage there are three essential elements: properly prepared photographs, detailed data on existing features and an accurate computer model. A number of photomontages can be prepared from within the site and from viewpoints in adjoining areas. The local planning authority is usually able to suggest viewpoints which will show the impact of the proposals on, for example, a conservation area.
Stereolithography
The use of computers is continually expanding and diversifying. Computer hardware and software have been developed using a computer-aided-design system to provide an exact plastic replica of an object designed on the screen. This process, invented by 3d Systems of California, is called stereolithography. It makes it possible to take a three-dimensional image from the computer screen and produce a three-dimensional object in a matter of hours. Only about 150 machines have been sold world-wide, but the market is growing rapidly and it is only a matter of time before this process is used by planners and architects.
Models and exhibitions
Once a model of the proposed development has been constructed it is possible to take photographs of it and the real life location, inserting the photograph of the model into the location photograph. Care has to be taken to ensure the compatibility of the two. The height, focal length, exposure and lighting must be directly comparable to obtain a realistic result.
As a really effective way of presenting a scheme to the public an exhibition can be mounted, displaying the plans, sections, elevations, perspectives, photographs and photomontages. If the exhibition can be located on or near the site, so much the better. This provides an ideal way of informing a key audience in great detail about proposals which could make a major impact on their immediate environment and it should be part of a complete communications package.
Environmental issues in all forms are at the forefront of the public conscience. The visual impact of high buildings is one of the important issues which planners and developers can control. Local planning authorities have a duty to protect and promote the public realm with all the means at their disposal. The increasing sophistication of presentation and interpretative techniques will enable the local authorities to gain in-depth appreciation of proposals, as well as allowing the developer to communicate his proposals accurately and sensitively.
