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The International Business Centre, in Moscow, Russia, has 50 storeys of commercial space with amenities such as a cafe and a landscaped roof garden. There are a further 20 floors of luxury residential apartments with their own pool and gymnasium on the 50th floor. The tower sits on a retail and entertainment podium that includes boutiques, restaurants, bars, a service hotel and a casino. In addition the tower connects with the existing retail concourse and metro system and has an underground car park for 800 cars.

As development land becomes scarcer and cities more densely populated, the appetite for mixed-use schemes is going to increase. We are now seeing central government and planning authorities actively encouraging mixed use in their planning guidance, as they see the benefits of this approach.

Within the mixed-use market, more schemes are now incorporating several uses in a single building. At their most basic level, mixed-use developments with ground floor retail and restaurant space with several storeys of residential accommodation above have formed the vibrant heart of towns and cities for many years. More complex mixed-use schemes were realised in the 1950s by visionaries such as Le Corbusier who pursued the idea on a large scale with his Unité D'Habitation model. These schemes typically included residential, retail, recreation and community functions.

Mixed-use schemes can deliver tangible benefits in revitalising city centres; whereas single-use schemes, while potentially more straightforward for the developer and more attractive for investors, can be seen as alienating because public access may be more limited. At worst, these developments can fail and become "ghettos".

The recent renaissance for mixed use started with relatively small projects comprising two or three uses; today much larger mixed-use schemes are commonplace. The large-scale redevelopment of the King's Cross area in north London with homes, office space, retail, leisure, health, education and cultural uses is one example.

With a mix of uses a building is likely to be occupied at different times and this brings life into an area throughout the day. This helps to promote a feeling of vitality and safety and therefore enables social and economic sustainability. In this way mixed use can re-introduce a sense of community into a city.

So what are the key considerations for the development of a successful mixed-use scheme? To consider the current popularity of these schemes we must look at the policy context within which this development is taking place.

Policy

Central government policy guidelines stipulate that 60% of new dwellings should be on brownfield sites. This encourages development on previously redundant and, at times, blighted urban sites. The sustainable communities agenda encourages higher residential densities and the inclusion of up to 50% affordable housing in city centres (in the case of London) and promotes the benefits of retail and leisure E E uses in creating and supporting sustainable communities.

At the local government level there has been a move towards unitary development plans - or their recent replacements, local development documents - that encourage mixed-use development and in particular planning briefs for particular sites stipulating this as a requirement.

Developers' response

As a result of these policies, developers have had to embrace the perceived difficulties and challenges of mixed use. They have had to be more creative with funding strategies for different elements and have had to understand the issues of complex mixtures of tenure - which affect the design of building circulation and space organisation.

Developers have found that while such schemes may be more complex, the necessity to consider mixed use to satisfy planning policy brings together a combination of uses that on the whole are complementary. And where financial risk is shared, lower-value elements are balanced by higher-value components that make schemes viable and sustainable.

ODPM research

With a mix of uses a building is likely to be occupied at different times and this brings life into an area throughout the day

As a result of the increase in the number of mixed-use developments in the 1990s, the ODPM commissioned research into this part of the market. Its findings, which are contained in the report, Mixed-use Development, Practice and Potential, were that mixed use is a desirable development objective in town centres. The report concludes that mixed-use development can play an important role "in creating the type and character of town centres which appeal to our intuitive aesthetic, social, cultural and physical precepts".

Examples of mixed use

Most examples of mixed-use development will contain a large element of housing, and each site will pose its own challenges.

Swanke Hayden Connell Architects is undertaking a scheme in Moscow which totals more than 2 million ft2 of accommodation. On a much smaller scale, SHCA designed a scheme for the Langworthy Road area of Salford.

In response to government's policies calling for keyworker and affordable housing, we are increasingly seeing large supermarkets and retailers incorporating residential components in their town centre developments. A good early example of this was Tesco's at Hammersmith in west London, which incorporated 100 apartments over the store for the Peabody Trust housing association.

In responding to the needs for new models of care for elderly people and for modernising primary care services and facilities, new mixed developments are being considered that bring these together to satisfy community needs.

Such schemes highlight another benefit of mixed-use development: that complementary uses can be grouped together, with each benefiting from the presence of the others. Furthermore developments that increase footfall will be more socially and economically sustainable.

The site in the Langworthy Road area of Salford is situated next to a group of streets where redundant Victorian terraces are being renovated by Urban Splash. Swanke Hayden Connell Architects’ masterplan for the church, community centre and housing scheme took on board the most appropriate location for the uses within the local context. The community centre and church, therefore, are on the main Langworthy Road frontage with a ribbon of residential development opposite the renovated Victorian terraces.

Funding challenges

Mixed-use developments present significant funding challenges and so are more likely to be undertaken by developers rather than institutional investors. Several of the larger housebuilders have also seen the potential of enhancing their town centre developments with other uses.

Although the funding for the development needs to be assessed as a whole, it is important that the market for each element is assessed to ensure that it can be sustained.

As the government's policy encourages mixed use it is possible to obtain grant funding for areas such as land remediation, housing, business and commercial and heritage conservation. This can be an important factor in establishing a business case for developments where any one of these issues, in isolation, could reduce the viability of a particular scheme.

Each use class will have different lease and tenancy arrangements - for example, retail/ residential/commercial - and these differences need to be considered in the funding strategy without compromising the scheme as a whole.

Design challenges

The market for each individual element must be assessed to ensure that each element can be financially sustained

The challenge for the designer of a mixed-use development is to create a sense of place and to arrange the different uses in the most compatible way.

It is essential to tie the development into the pattern of movement through the town or city so that a building can be woven into its fabric. Extensive research has been carried out by specialist companies that analyse and predict the movement of people through particular spaces, and the design must respond to this in order to be a success.

There can be opportunities to provide elements for social interaction, and elements that change and bring diversity in the use of the building. It may be possible to overcome complex circulation issues and actually form a creative "pinch point" to enable this interaction rather than separate the various uses.

The design will also need to resolve potential incompatibilities that different uses may present. These may involve the servicing requirements of retail spaces, the amenity spaces for residential areas and the need for acoustic and visual separation between areas with different uses.

Vehicular circulation and parking allocation need to be considered carefully where uses are compatible. For instance, where there are commercial and leisure uses together, there can be considerable benefits to sharing car parking spaces to reduce the overall parking requirements.

Compliance challenges

For each class of use there will be different legislation and guidelines, and these may have conflicting influences that need to be resolved. The added complexity of different uses in close proximity will require careful zoning and a well executed approach to issues of fire safety and separation to avoid an excess of vertical circulation.

The new ºÚ¶´ÉçÇø Regulations, due to come into force this year, will place even higher standards on thermal performance to add to recently enhanced requirements for sound attenuation and disabled access.

Benefits

The benefits of mixed-use developments are clear. Schemes that include a wide range of uses from residential through to commercial and leisure activities can form the basis for a vibrant sustainable community.

The ODPM research concluded that the demanding planning and design process involved in complex mixed-use schemes drives up the quality of the finished scheme.

The positive effect of locating complementary uses together means that they mutually support and enhance the success of each other. In the case of a primary care centre scheme with extra care housing for older people there are clear benefits to both doctors and residents.

An additional benefit where residential and employment uses are co-located is the potential for reduction in commuting which inevitably leads to a better work-life balance.

A building that is more compactly planned will also inherently be more energy-efficient and engineering strategies can be developed that enable each part to contribute to the energy requirements of the whole.

Finally, mixed-use developments make very efficient use of land compared to single-use developments as they are more likely to be on sites where increased densities can be supported.