Forty years ago this year Unesco (United Nations Educational, Scientific and Cultural Organisation) adopted the World Heritage Convention. This ambitious project set out to identify world heritage sites – places that are deemed to have outstanding universal value (or OUV) for all mankind. The announcement triggered a worldwide scramble for recognition and there have now been 936 successful nominations. Of the world heritage sites, 183 are natural wonders such as the Grand Canyon and the Victoria Falls. The remainder are cultural sites and include the world’s most famous monuments: the Egyptian pyramids, the Acropolis and Stonehenge.

While identifying a stretch of coastline or a remote group of standing stones as a world cultural icon is relatively straightforward, drawing a line on a map in Yaroslavl, Panama, Naples or Lijiang is not so easy. Decisions have to be taken as to where the OUV starts and stops and, more controversially, how large a buffer zone the site needs around it to be protected from invasive development.

As reported by the Financial Times on March 6, a massive development in the Liverpool docks in the UK was approved by the city council. This mixed-use mega-project will eventually bring 9,000 apartments to the city. Views from the 50th floor of the highest tower will be spectacular, looking over the River Mersey and the world heritage site in the city centre. But heritage bodies led by Unesco are aghast. These blocks of flats will, they argue, detract from the OUV.

The question for Liverpool and the UK government is whether Unesco place their world heritage site on its danger list? This list of around 35 sites is the tool that Unesco uses to monitor and shame countries that it believes are threatening the OUV of their sites. Unesco’s ultimate sanction is to delist a site if it feels that the OUV has been destroyed. This is what happened in Dresden in 2009 due to the effects of a new four-lane bridge.

Urban developments, such as the project in Liverpool, are a particular concern for Unesco. The case that defined the issue was Vienna, which already had plans to develop tall buildings on the periphery of its world heritage site when it was listed in 2001. The intention was to redevelop the area round the Wien Mitte station, including a cluster of high-rise buildings, the tallest of which was to be 97 metres. This generated widespread concern that historic Vienna’s tallest building, the cathedral (only 800 metres away), would be overwhelmed.

The city of Bath in the UK

In 2003 the mayor of Vienna stopped the scheme, but not before work had begun on the 87-metre City-Tower in Marxergasse, a commercial development of reddish sandstone capped by a swivelled glass cube. The Vienna case was regarded as a victory for the moral power of Unesco and led to the Vienna Memorandum – a Unesco policy statement about urban development.

Written in dense Euro-speak, the memorandum is binding on nobody and has plenty of latitude for interpretation. However, it does reinforce the fundamental recognition that people want to live and work in and near world heritage sites because they are beautiful, historic places and, as a result, generate high property values. Office, hotel, retail or residential developments with a tremendous view of a world heritage site will command a premium, and here the problem lies. Developers and politicians want to develop their protected city centres to draw in wealthy residents, tourists and businesses and the only way they can build is up. In doing so they are likely to incur the wrath of Unesco.

In 2010 Unesco analysed the threats to world heritage sites reported to its Paris headquarters over the previous five years. The percentage of threats from development and infrastructure rose from 52.6 per cent in 2005 to 74.5 per cent in 2008 before falling, presumably as a result of stalling development, to 67.8 per cent in 2009. It is not possible to draw out the percentage of development that was specifically residential, but Unesco’s figures show that threats from new building rose from 32.1 per cent of the total to more than 51 per cent in 2008 before falling to 41.8 per cent the following year. Threats posed by tall buildings on cultural world heritage sites rose from 3.2 per cent in 2005 to 7.2 per cent in 2009.

Old meets new in George Town, Malaysia

The historic centre of the Chinese city of Macao is one of the world heritage sites that Unesco is concerned about. The site encapsulates the historical relationship between western and Chinese civilisations and its streets are lined with buildings that blend Portuguese and Chinese traditions. At One Central, a tall residential development on the Nam Wan Lake on the edge of the world heritage site, flats are marketed as being for “people that value living in luxury on the edge of Macao’s downtown world heritage sites”. Can you blame them? The views from the tower are indeed spectacular but the issue, of course, is not the view but what the tower looks like from the historic centre. Unesco believes that tall buildings undermine the overall legibility of the Macao world heritage site, in particular the visual links between the town and the wider land and seascape that emphasise how Macao became a trading port in a major commercial sea route. This might sound a bit prissy to developers but it is a real and present issue for the authorities who have Unesco breathing down their necks.

Another world heritage site that has similar problems is Melaka and George Town on the Straits of Malacca, Malaysia, inscribed for its remarkable blend of Asian and European architecture. George Town is characterised by its late 18th-century British colonial buildings. Here developer Asian Global Business (AGB) proposed a 13-storey mixed-use development that was to include upmarket city apartments. The plan resulted in a storm of protest and AGB drastically remodelling its proposals, dropping the residential part to only five storeys built in a quasi-colonial style.

The surprising thing is that planning authorities in George Town should take so seriously the blandishments of Unesco’s expert committees, but they are not alone.

The huge mixed-use Okhta Centre in St Petersburg, which was to pivot on the tallest building in Europe, the Gazprom tower, is now in limbo due to the outrage of conservationists. The St Petersburg world heritage site, which includes the Hermitage, is characterised by a “celestial line” – the horizontal panorama of rooftops that reflects the surrounding landscape. To protect it the city had strict height controls but the Gazprom tower broke all the rules and raised opposition from local residents and the international community. New schemes will be brought forward for the site that, on the right bank of the Neva river opposite the Smolny Cathedral, will remain a desirable place for development.

The Shard seen behind the Tower of London

It is remarkable that Unesco has, with no real sanctions other than shame, managed to make a considerable impact on the planning policies of its 182 urban world heritage sites. This is not confined to developing countries wanting to belong to a European club. After Unesco missions to London and Liverpool in 2006 the former UK planning minister Yvette Cooper introduced powers to deal with controversial planning applications in world heritage sites. Indeed there is a sense in which cities in the EU have come in for special criticism as they “should know better”.

Nobody has yet attempted to calculate the premium that people will pay for living in or overlooking a world heritage site, although the economic advantages of such places in terms of tourism have been investigated. Yet there is no doubt that developers will continue to see the value generated by tall buildings with sensational views of world cultural icons. What is surprising is that Unesco’s fuzzy concept of outstanding universal value and its wordy resolutions have had so much success. Developers with vast sums at stake put considerable resources into finding ways to build in and around world heritage sites. Those that are successful, such as the Sellar Property Group, the company behind the Shard in London with its view over the Tower of London world heritage site, could make a great deal of money.

The 10 most alluring world heritage sites to live in

1. Split, Croatia, inscribed 1979: live in the remains of an ancient Roman palace.

2. The Stone Town of Zanzibar, Tanzania, inscribed 2000: Swahili trading port that time passed by.

3. Bruges, Belgium, inscribed in 2000: great food in romantic medieval streets.

4. Old Havana, Cuba, inscribed in 1982: gently decaying bohemian charm.

5. Campeche, Mexico, inscribed 1999: beguiling fortified colonial port on the Caribbean.

6. Venice, Italy, inscribed 1987: so famous it hardly needs to be a world heritage site.

7. Carcassonne, France, inscribed 1997: medieval fantasy, but beware tourist blight.

8. City of Bath, UK, inscribed 1987: elegance, sophistication and shopping.

9. Medina of Marrakech, inscribed 1985: more shopping, in old-world Arab centre.

10. Macao, China, inscribed in 2005: east meets west in cosmopolitan port.

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