Specialist stone contractor S McConnell & Sons shaped and installed the dramatic basalt walls and paving of Heneghan Peng’s new visitor centre at the Giant’s Causeway in Antrim, Northern Ireland, that opened in July.

The new visitor centre at the Giant’s Causeway in Antrim, Northern Ireland, with its 209 basalt columns, is made from the same stone that forms the World Heritage Site of the Causeway – built, according to myth, by the giant Finn MacCool.

The Visitor Centre disappears into the landscape, creating unreal vanishing points that make the visible exterior walls look as if they stretch into the far distance. A polished wall at the back of the car park, rubble walls around the car park and all the hard landscaping (1,600m2 of paving with 2,100 linear metres of kerbs) is also made of the basalt.

The smooth basalt columns that, combined with glass, form the facade, rising out of and fading into the ground, create a modernistic interpretation of the Causeway for visitors to the site – and the new centre is intended to facilitate a 30% increase in the 600,000 people a year that the Giant’s Causeway usually attracts.

The stone was not, of course, taken from the Causeway itself but from Craigall Quarry, operated by Patrick Bradley Ltd at Kilrea about 50 miles away.

The quarry blocks were initially taken for processing to

S McConnell & Sons’ well-equipped masonry factory 80 miles from the quarry at Kilkeel in County Down. But the quarry produces aggregates, where the rock is blasted, and there was so much waste in what was being delivered to McConnells that for every five lorry-loads of block coming into the factory only one lorry-load of finished product was going to site. The rest was being returned to the quarry to be crushed as aggregate.

So a second-hand BM Diamond 40 with a 2m blade and a generator to power it was put into the quarry to reduce the cost of transport. Waste was further reduced by McConnells working with the quarry operator to recover the largest blocks possible using a low power blasting technique and with the architects to keep the finished stones a reasonable size for the material being worked.

The columns are solid stone. There are 124 of them less than 300mm wide that have been post-tensioned to hold them securely in place, while the larger columns stand on their own. None of them is load-bearing, with the weight of the grassed, concrete roof being carried on steel columns that are positioned every 6m with the stone around them.

The floor is also concrete, although the concrete has used the local basalt as the aggregate, largely to utilise locally sourced products and keep the carbon footprint down for the BREEAM rating (which is ‘Excellent’ – see page 20).

The elements of the design are non-orthogonal and oriented diagonally across the development. This grid stretches out into the paving, with all the diagonals lining up. Accurately maintaining the grid called for some exceptionally accurate production and fixing of the stone by McConnells.

It also means few of the 40,000 stones are the same as any other, which was another challenge for the stone specialists, although having one of the most technologically advanced factories in the UK, as well as a highly skilled workforce, meant they were up to the challenge.

The development took two years to build and McConnell’s fixer-masons were on site throughout last winter. They say there are more pleasant places to be on a winter’s day than working on the top of the cliffs on the north coast of Ireland.

In spite of the difficulties, Alan McConnell, the Managing Director of his family’s stone company, says he guarantees the stone was no more expensive than if it had been imported, although he says: “They got a bargain.”

The £18.5million, 1,800m2 development was designed by Róisín Heneghan of architects Heneghan Peng, the internationally reknowned practice founded by Shih-Fu Peng and Róisín Heneghan in New York in 1999 that relocated to Dublin in 2001. The Centre was paid for with contributions from the European Regional Development Fund (ERDF), Northern Ireland Tourist Board (NITB), Heritage Lottery Fund (HLF) and the National Trust, which manages the Giant’s Causeway site.

The design was chosen as the result of an international competition in 2005 that attracted 201 entries from across the World.

Unveiling the winning design, Peter Hain, Secretary of State for Northern Ireland at that time, said: “This design is a stunning piece of architecture, providing a unique space for visitors from all over the world to appreciate the natural beauty of Northern Ireland’s only World Heritage Site.

“This project is one of the most important developments for Northern Ireland’s tourism industry in many years. As a signature project of truly international appeal, the new Visitors’ Centre will significantly enhance the Causeway’s attraction for tourists and will help Northern Ireland realise its full tourism potential.”

The National Trust’s Project Director for the Visitor Centre was Graham Thompson. He describes the building as a concrete shell with a grass covered concrete roof supported by a series of internal and external steel beams. Much of the building is below ground, but where it emerges it is the basalt that is predominant.

Graham says in the early stages of the project a report was commissioned to identify the source of the local stone that would be used – there being a dozen or so quarries in the area producing the basalt as aggregate but there being no specific dimensional stone quarry.

“We were very keen not to follow the route of most people these days of importing from Brazil or China. We identified stone about 50 miles away that we believe is from the same lava flow as the Giant’s Causeway.”

Although the lines of the building are clean and precise, the aim was to reflect the fact that, although the stones of the Giant’s Causeway appear to be geometrical hexagons, they are not. It is believed the formation was created by the shrinking of cooling lava and the way tension has been released results in a lot of six-sided stones. But they are neither all hexagons nor regular.

The apparent regularity that closer inspection belies is intentionally reflected in the stone of the Visitor Centre. “Each mullion uses a different configuration of stones, so no two next to each other are identical,” says Graham.

The paving is also various sizes while precisely following the diagonal grid across the site, that has been adhered to remarkably well. The paving was originally going to use much larger slabs but for practical reasons a smaller size was accepted.

The innovative and imaginative building was opened on 3 July, when it was visited by a delegation that included the Northern Ireland First Minister, Peter Robinson, and Deputy First Minister Martin McGuinness.

There is only one small criticism from this magazine’s point of view, which is that the glazing allows views of the edges of the concrete roof plate. They could have been covered by basalt, as the spaces between the columns at the ends, where there is no glazing, have been. It is no doubt intentional and shows integrity but looks unfinished.

The interior houses an area where non-National Trust visitors pay the £8.50 that it costs to see the Giant’s Causeway. There is also a shop, cafeteria and an interpretation area where people can browse through the building. Or you can follow a fast-track route to the exit point to catch a shuttle buses down to the causeway, if you do not want to take the 10-15minute walk down.

The new centre has a new car park, with the polished basalt wall at the back of it and rustic basalt rubble walling as other perimeter walls, offering car parking in addition to the existing car park. There is also a park-and-ride at nearby Innisfree.