At Euro1,220 (just over £1,000) per square metre, the new development at Limerick University challenges the view that using natural stone has to be expensive. Yet the project was considered good enough to be short-listed for the RIBA Stirling Prize last year.

Stone specialists have often said that if they are consulted at the design stage of a project they can save clients a lot of money by offering advice on how to make best use of the stone. The new Medical School at Limerick University is the proof of that.

The advice does not always have to be accepted. There can be a conflict between a designer’s desire to use the largest size of stone possible and the most economical way of using that stone – which is always likely to be to use smaller elements because there will be less waste.

At the University of Limerick, Dublin and London consultant Carrig was engaged to advise on the use of the stone that Grafton Architects, an Irish practice, wanted to use.

The stone would convey the gravitas of the 1,800m2 medical school it was to be used on as the centrepiece of this part of the campus, which also includes two new student accommodation buildings. The student accommodation is brick, but has been designed with deep window reveals in sympathy with the stone design of the medical centre and incorporating sloping cills of limestone to reinforce that unity.

The stone used is Irish Blue limestone to reflect the geology of County Clare, home of the Burren, Europe’s largest area of limestone pavement. Although the Medical School is part of the University of Limerick, the campus straddles the River Shannon, which forms the boundary between County Limerick and County Clare, and the new building is on the Claire bank of the river.

The new Medical School is in an area of natural beauty next to the river. The area has been newly landscaped to create a communal piazza, the Irish Blue limestone paving and wall-top seating carrying the theme throughout the area.

The stone for the project was supplied by Stone Developments. The company, then part of the Sisk group and taken over by Belgian stone company Brachot-Hermant just before Christmas (see NSS December 2013), produced the sanded 80mm cladding blocks for the building, the 40mm bush-hammered paving, and the cills, soffits, coping and seat tops with a bush-hammered finish.

The structure of the Medical School is a poured concrete frame with block infill and the stone tied back to it through a 100mm insulated cavity. Some of the frame is still on view both inside and outside the building – as you can see in some of the pictures here. The architects wanted to use 80-100mm hand-set cladding in random lengths between 500mm and 1100mm for the outside walls because they particularly wanted a traditional stone-built look that included lime mortar pointing.

Although the stone on the project has been used in small sizes, it has achieved a standard worthy of consideration in the Stirling Prize because it was carefully produced to a detailed, 25-page procurement specification written by Carrig.

“We were very specific about what was acceptable,” says Carrig Director Peter Cox, although not quite as specific as architect Shelley McNamara had originally wanted to be in terms of the uniformity of the appearance of the stone. Too much uniformity can strip natural stone of its essential character as well as adding considerably to the price.

Having Carrig on board produced the best of both worlds, from an aesthetic perspective and cost, even though a curved ball was thrown into the project when the initial contractor went bust half way through construction and what was left of the project had to go out to tender again.

The stone selected was from Stone Developments’ Bed ‘E’ of its Old Leighlin quarry in Co Carlow, a bed that is light in colour and low in variation and fossil content. “Thankfully Shelley McNamara went with what we proposed and it looks absolutely fantastic,” says Peter.

Carrig remained on the project during construction, which was just as well as there were issues such as the connection between the windows and the stone. The windows were specially designed but that design would throw too much rainwater on to the stone, which could have led to streaks and accelerated decay. By being on-site, Carrig was able to resolve the issue before the walls were built by incorporating hidden gutters. “We were talking before rather than arguing afterwards,” says Peter Cox, which saved a lot of conflict and money.

Shelley McNamara did consider other stones apart from the Irish Blue but in the end decided the Irish Blue was attractive and appropriate – and would be particularly environmentally friendly as it had so little distance to travel.

The RIBA Stirling Prize judges clearly agreed that it was a good choice. The Stirling Prize is recognised internationally as one of the most rigorously-judged awards for architectural excellence. There were six buildings short-listed for it last year, two of which were in Ireland (the other was in the North; the Giant’s Causeway Visitor Centre featured in NSS August 2012 with its columns of basalt reflecting the natural geological feature of the Giant’s Causeway) and four of which involved major elements of stonework.

The winning project was Astley Castle, where stone and conservation specialist William Anelay helped create a new-build within the walls of the castle ruins in what this magazine described as “conservation through re-use” when it featured the project, then in progress, in 2011 (see NSS July 2011).

The Stirling Prize short list was drawn up from among 52 national and international award winners. In introducing the short list, RIBA (Royal Institute of British Architects) described the University of Limerick Medical School as “an exceptional example of how to create a vibrant new public space through the careful design and placement of buildings”.

Although the new Medical Centre is 30m x 60m and the stone has been used to emphasise its solidity, the bulk has been broken up by a number of features that add interest and lighten the whole structure.

Not least is the geometry of the building, with its angles in the walls and roof and the stone-clad fins at various angles – attractive, but adding complexity to the stone contract. Expansion joints are hidden by overlapping the stones. There is a colonnade along one side which, seen from the piazza, creates an effect similar to that of placing mirrors facing each other on parallel walls (see the main picture on page 18). Grills created by omitting stones punctuate the mass of walls where there are no doors or windows, and wood and glass interact with the light and shadow on the stone that constantly changes the faces of the building as the sun moves across the sky.

And it is not just aesthetic. The deeply recessed large windows are shaded by the stone panels to stop the building overheating on bright days while allowing plenty of daylight to penetrate the building – more, in fact, than the windows in the walls would indicate because there is also glass in the roof, lighting the centre of the building.

The durability of the stone and its resistance to weathering were another part of the plan, reducing maintenance. And, again, Carrig played its part in ensuring the stone would perform as required.

Carrig was approached by Grafton because the two practices had worked together previously on the new Department of Finance building in Dublin, which has its similarities to the Limerick building.

“Shelley McNamara came back to us because she liked the fact that we could give her this comfort factor from an independent standpoint,” says Peter Cox. “Quality is what she emphasises every time.”

Carrig Building Fabric Consultants Ltd

Carrig was established as a consultancy for the heritage sector and that is still where it carries out most of its work, although Director Peter Cox says: “20% of our business now is advising on new build, mainly because architects do not have great expertise in stone.”

Carrig’s first consultation on a new build was in the UK, in Birmingham, with Seymore Harris Architecture. The architect was building a new, 11-storey National Westminster bank. Carrig, which was established initially in conjunction with Trinity College Dublin (which still owns 6% of the business), takes a strongly scientific approach to all stone issues. The successful conclusion of the NatWest project led on to other new build projects in the UK, Ireland and elsewhere in the world and has remained part of the Carrig mix ever since.

Carrig was approached by Grafton Architects about Limerick University simply because the architects had consulted Carrig previously and had been happy with the outcome. They wanted a stone expert on board for Limerick to supplement their knowledge.

Peter: “We will sit down with the architect and discuss what they want. Then we will work with them on the design, highlighting problems such as shedding water. Then we write a really tight specification for the stone, so we don’t get a ‘that-will-do’ attitude from the supplier. We like to keep an eye on a job, so if any stone isn’t right, it is returned.”

It is not always the architect who approaches Carrig. The company often acts as a consultant for contractors, especially if they are encountering a particular design proposition for the first time.

But the heritage sector still forms the greater part of Carrig’s workload and one of its current projects is at the City Hall in Liverpool. A large, distinctive building of a pinkish sandstone, City Hall had stood out like a beacon to the Luftwaffe during World War II, so it was painted black. But what had been used to paint the building was defying analysis. Carrig discovered Liverpool had linseed oil and boot polish factories during the War and the products from both had been mixed to make the paint that has proved so difficult to remove ever since. Discovering what it was informs how it can be removed. “We’re building detectives – CSI Stone,” says Peter.