The former Bank of Ireland headquarters on Lower Baggot Street changed hands for a king's ransom during the boom, when it was sold to a consortium headed by Derek Quinlan and Paddy Shovlin for €180 million. Then, after the crash, canny meat baron Larry Goodman snapped it up for €50 million.

Fortunately, the man who survived the beef tribunal is fully aware of the the architectural importance of this bronze-clad office complex from the early to mid-1970s. He also bought it knowing that its original façades and external spatial arrangement are listed for preservation.

It is now one of the relatively few 20th-century buildings in Dublin to be designated as a protected structure. Designed by Scott Tallon Walker (STW), its importance derives from the fact that it was modelled in detail on Mies van der Rohe's classically modernist Seagram Building on New York's Park Avenue.

The cladding of Delta manganese bronze is exactly the same, even down to its fetishist “double re-entrant” corners, but the form is different. Seagram is a 38-storey “skyscraper” – now nearly dwarfed by more recent towers – whereas the ex-Bank of Ireland HQ is a complex of three relatively low-rise office buildings.

The biggest one, at the rear, is eight storeys high above a podium and its bulk is cleverly concealed by the two lower buildings at the front to minimise its impact on the Georgian streetscape. That being said, its development (between 1970 and 1978) required the demolition of an intact terrace of five Georgian houses.

An entirely unsympathetic scheme, designed by HKR Architects for the Quinlan/ Shovlin consortium, would have added so many new elements to the complex that it would have become nearly unrecognisable. Fortunately, there was such an outcry over what was being proposed that Dublin City Council refused permission.

Now, Scott Tallon Walker is back in the driving seat and its client – Larry Goodman's vehicle Remley Ltd – is committed to carrying out a thoroughgoing refurbishment of the existing complex while adding to it sympathetically by extending the largest block by a single bay to the rear and topping it with a penthouse level.

"We only wanted to be involved with someone who'd respect the building," says Michael Tallon, STW managing director and son of the late Ronnie Tallon, who designed the original complex as a homage to Mies. "We had our own view on what an appropriate response would be and Remley is very supportive of the scheme."

He says his father, who died last month, had been involved in discussions about it all over the past year and was “very comfortable with the approach we’re taking. It’s also been refined a number of times and is at a fairly advanced stage now. We believe it’s very respectful of the original design philosophy.”

Project architect Ronan Phelan says the complex would be "completely renovated, restored and refurbished" to the highest standards of modern office accommodation, with raised floors, upgraded services and new bronze-tinted double-glazed windows that would lift its energy performance to Leed gold or platinum.

“The BER [building energy rating] is about G at the moment,” he said, adding that the Seagram Building is also a notorious gas guzzler.

"The US Green Building Council is very excited about this project and looking at it as a way of benchmarking how curtain-walled office buildings from the 1970s can be brought up to standard."

The façade is the biggest challenge. It has weathered over the years to a grey- green patina in places, with the ground- floor level painted over. Under the refurbishment plan, the paint will be removed and the evidence of weathering stripped back and “re-patinated” so that it will look just as it did in the 1970s.

The architects are lucky that floor-to- floor heights are generous enough (at 3.6 metres) to allow for raised floors and suspended ceilings to conceal services. Granite used to clad the high walls of the foyer will be taken down, cleaned and put back up, but bathrooms and lifts all need to be replaced.

The granite paving of the forecourt and podium would also be relaid, the main entrance (currently quite small) would be enlarged and the very generous ground floor – which, unusually, rises to six metres – stripped of a mezzanine level added later to reinstate its original Miesian proportions.

The main service core is to be relocated to open up views through the main block, while the addition of a gym at the rear and the installation of 156 bicycle parking spaces at basement level, with access from James’s Lane, should help to “animate” this area. Unusually, car parking spaces are being cut from 180 to 120.

Not only do all of the Scott Tallon Walker drawings of the Bank of Ireland headquarters still survive, but also Smith & Pearson’s construction drawings.

It is not the first time this long-established practice has renovated one of its older buildings: the former Carroll's factory was adapted for Dundalk Institute of Technology.

“There will be no compromise on quality,” Tallon says. “The work we’re doing is being done for the next 35 to 40 years. And we’re delighted to be involved [in refurbishing the building] because it’s near and dear to our hearts, as it was to Ronnie’s.” This time, however, it will even include a “green roof”.

The proposed extension, which would increase the floor area of the complex by 5,000sq m (to 18,000sq m), is being done in the most sympathetic way possible – by adding a bay to the rear of the eight-storey block, running its full length, topped by a penthouse level that would also conceal mechanical plant.

Tallon believes the increase in bulk would be almost imperceptible, and he’s probably right – because one of the truly ingenious aspects of the original scheme is that the scale of the main block can only be seen from the rear, on James’s Lane, or from afar – the north side of St Stephen’s Green, for example.

A planning application is to be lodged soon seeking permission from Dublin City Council for the proposed extension, which Tallon says would enable much better, more “agile” office layouts on each floor of the main building.

It would suit a corporate headquarters, or perhaps even three of different sizes – one in each block.