LONDON.- The beautifully simple Velodrome in London's Olympic Park, the carefully crafted remodelling of the Royal Shakespeare and Swan Theatres in Stratford upon Avon, a highly imaginative London school on a tight urban site, an innovative and vibrant cultural centre in Derry, the transformation of an unremarkable 1980s office building in London into an elegant new office and retail space, and the breathtaking extension of a significant museum in Germany, form the shortlist for the prestigious £20,000 RIBA Stirling Prize.

Now in its 16th year, the RIBA Stirling Prize in association with The Architects' Journal and Benchmark is awarded to the architects of the best new European building 'built or designed in Britain'. The winner will be announced on Saturday 1 October at Magna Science Adventure Centre in Rotherham and will be broadcast on a special edition of BBC Two's The Culture Show on Sunday 2 October, presented by Kevin McCloud.

This year is the first time the shortlist includes practices who have all previously been shortlisted for the RIBA Stirling Prize; and also includes two RIBA Stirling Prize winners: David Chipperfield Architects and Zaha Hadid Architects.

Ruth Reed, RIBA President, said: 'The RIBA Stirling Prize celebrates architectural excellence and this year we have another outstanding collection of culturally significant buildings on the shortlist; projects that have each made a significant contribution to the evolution of architecture.

Creative redevelopment is a strong theme in this year's list, with a major museum extension, a remodelled theatre complex and the innovative retrofit of an old office building featured, showing how even with tight planning and building constraints, talent and imagination can totally transform existing structures and sites. From recycling to cycling: this year's shortlist features the first Olympic venue, a beautifully clever exemplar for the UK's Games. Another 'first' is a significant cultural centre in Derry, Northern Ireland's first building to make it onto the shortlist. Finally I am delighted to see a brilliant academy on a tight urban site completing the list; a school project that demonstrates what can be achieved when the architect and clients 'think outside the box'. I look forward to seeing which project the judges select as the worthy winner.'

The 2011 RIBA Stirling Prize judges who will visit the six shortlisted buildings and meet for a final time on the day of the presentation to pick the winner include: Angela Brady, Chair of the judges and RIBA President (commencing September 2011); Sir Peter Cook - architect and academic, formerly of Royal Gold Medal winning Achigram; Hanif Kara - engineer, Adams Kara Taylor and Dan Pearson - landscape designer and RIBA Honorary Fellow.

Previous winners of the RIBA Stirling Prize include: MAXXI Museum, Rome by Zaha Hadid Architects (2010); Maggie's Centre at Charing Cross Hospital, London by Rogers Stirk Harbour + Partners (2009); Accordia housing development by Feilden Clegg Bradley Studios/Alison Brooks Architects/Maccreanor Lavington (2008); The Museum of Modern Literature, Marbach am Neckar, Germany by David Chipperfield Architects (2007).

The shortlisted works are:

An Gaelaras
Derry, Northern Ireland
Architect: O’Donnell + Tuomey • Client: An Gaelaras • Contractor: JPM Contracts • Contract Value: £2.8 million • Date of completion: Sept 09 • Gross internal area: 1980 sq m

An Gaelaras is a cultural centre designed to promote the use and enjoyment of the Irish language and its culture. Faced with an almost impossible landlocked site (only one of the four sides was able to have windows) in a street of Georgian and Victorian terraces and further compromised by a substation that occupies a third of the frontage, the architects have come up with an intriguing and intricate vortex plan that draws the visitor in and up the resulting dynamic multilevel building. With only one external elevation they have created three other facades internally. Lots of architects talk about creating ‘streets’; this one really is. The cranked space, toplit by a large steeply sloping rooflight, transports you as if to a twisting mediaeval lane in an old city. Shops, cafes, bars are all there and lead you through to a theatre. Above, teaching and office spaces jostle for views, linked by a series of stairs, bridges and platforms that circle and cross the internal courtyard. The stairs appear and disappear as the route unfolds like an unpeeling orange, making visitors want to explore whilst drawing them up both visually and physically to the upper levels. The plan appears haphazard but in fact it fixes places and connections. Herein lies the success of An Gaelaras: its ability to house all the different functions within spaces that have adequate light and views despite being inside a building with limited aspects and whose only elevations are the front and the fifth one: the roof.

The sense of the building as a sculptural intervention in a conventional street is enhanced by the use of beautiful board-marked concrete. In scale it respects its neighbours but materially it is very different and speaks of culture as something that is aspirational as well as communal. The concrete adds gravitas and allows for the use of cheaper materials elsewhere: plywood and painted plaster.

An Gaelaras is an innovative and vibrant building that embodies the celebration of Irish language and culture using a dynamic plan form to break down convention and enhance the sense of community. The organisation and the aesthetics complement one another to produce a rigorous piece of architecture that characterises the institution instead of merely reflecting the predelictions of the architects.

The Angel Building
St John Street, Islington, London N1
Architect: Allford Hall Monaghan Morris • Client: Derwent London • Contractor: BAM Construction • Structural Engineer: Adams Kara Taylor • Services Engineer: Norman Disney & Young • Contract Value: £72m • Date of completion: October 2010 • Gross internal area: 33,224 sq m

This speculative office space redefines the sector. An unremarkable 1980s office block has been transformed into a building not only of great elegance and poise but one that contributes positively to life on the streets outside while creating new interiors of great refinement.

A new tailored facade to St John Street sweeps round the corner with the Pentonville Road, connecting with the set-back building line established by a neo-Georgian neighbour and creating a new landscaped strip, designed by J+L Gibbons. The shimmering trees form a foil to the crisp lines of the new facades and help to aerate this busy part of Islington.

The new building retains the original structure while infilling an old courtyard and adding new office girth around its perimeter. The additional floor-space (25,000 square metres net of lettable space instead of 15,000 square metres) is the key to increasing the building's rental value, unlocking the development and enabling it to become more intimate with the surrounding streets. Retail units – including a soon-to-open Jamie Oliver restaurant - are incorporated into the ground floor on St John Street.

The entry sequence off St John Street with a publicly accessible cafe and lounge sets civilised new standards for ways in which the atrium form can be used to animate a commercial ground floor as well as simply getting light in. A finely executed and generous 3 metre grid of in-situ concrete fins and beams (instead of the usual enslaving 1.5 metres) rises up to a gridded toplight. The colour and smooth surface of the concrete is complemented by the smaller scale grid of a delicate terrazzo floor.
A magnificent polished black gestural sculptural piece by McChesney Architects Out of the strong came sweetness adds drama and counterpoint to the Kahnian gravitas of the atrium.

It is to the huge credit of Derwent London plc with their architects, AHMM, that they have created such high-end speculative office space. The building is not only extremely well made and resolved, but offers an idea of how building and working in cities might look in the future.

Evelyn Grace Academy
Shakespeare Road, London SE24
Architect: Zaha Hadid Architects • Client: ARK Schools • Contractor: Mace Plus • Structural Engineer: Arup • Contract Value: £37.5m • Date of completion: 2010 • Gross internal area: 10,745 sq m

This is Zaha Hadid Architects first large-scale project in the UK: a school situated in the ward with the highest crime rate in Western Europe.

The architects received a complex brief: four schools under a single academy umbrella with the need to express both independence and unity. This is a large school on a small site, occupying just 1.4 hectares, whereas the average secondary school takes up 8 hectares. Curiously for a school whose speciality is sport, the original site seemingly lacked any opportunity for significant outdoor sport but the architects have responded with guile and intelligence, providing a multi-use Astroturf pitch which can be used for football or simultaneously by games requiring smaller playing areas. In one corner of the site they have even found room for a wildflower garden. The project is distinguished by its planning not its formal expression; its saltire (Scottish flag) plan solving multiple demands of site and usage in a manner that seems effortless.

There are two entrances to the street, one on either side of the site. It is cut in half by a bright red 100 metre sprint track with the school building diagonally bridging the track. Entrances to the buildings are at the half way point.

The school is planned in the shape of a 'Z'. Entrances and terraces are woven into the wings so that pupils are dispersed throughout the site between lessons. Internally the academy is a good quality and functional modern school, with occasional moments of architectural drama which serve as reminders that this is architecture and not just building, though not in any way at the expense of utility or value. At the outset the architects decided against having an atrium that has become a trope in the design of so many academies. Instead of wasting space, and therefore money, in this way, they spend wisely on better designed and lit classrooms and wider corridors. Also on the big rooms on two floors at the heart of the plan which can be divided by acoustic screens into dining, teaching, assembly, drama and indoor sport areas.

This is a design that makes kids run to get into school in the morning.

Folkwang Museum
Essen, Germany
Architect: David Chipperfield Architects • Client: Neubau Museum Folkwang Essen GmbH on behalf of the Alfried Krupp von Bohlen and Halbach-Stiftung • Contractor: Ingenieurberatung Pühl and Becker VBI, Seroneit and Schneider • Contract value: Confidential • Date of completion: April 2010 •Gross internal area: 24,800 sq m

Folkwang Museum is a breathtakingly accomplished design. Located in Essen, in the industrial Ruhr region, it extends a beautiful late-1950s designed Miesian museum by the city architects and develops the principles established by the existing structure, much as a jazz musician might riff on the tune of a classic song. The result is a genuinely uplifting, light-filled public space, offering a serene and yet mesmeric mixture of inward-looking courtyards and external views out.

Its external cladding is of large panels of crushed recycled glass, giving a shimmering translucent finish which has more of the qualities of alabaster than glass. Inside, carefully detailed top-lighting systems in the galleries blend natural and artificial light and are of course capable of being completely blacked out. In the large, flexible temporary exhibition space, the lighting grid has been coordinated with a bespoke flexible but highly stable partitioning system than can easily be assembled and remounted to meet the requirements for each show.

David Chipperfield won the international competition organized by the city of Essen in 2007 and the building opened in time for Essen and the Ruhr to become the latest European Cultural Capital. The new building continues the architectural principles of the old one with an ensemble of six structures and four interior courtyards, gardens and corridors. All the galleries and ancillary rooms (old and new) are connected with no changes in level. A large open stairway leads into an extraordinarily spacious new entrance hall, conceived as open interior courtyard with a café, restaurant and bookshop. There are also a library and reading room, a multi-function hall, art-stores and restoration workshops.

Since it re-opened in 1960, (its predecessor having been badly bombed), the museum has been a meeting room for the city as well as home to a world-class collection of 19th and 20th century art. Passers-by on the street and even people sitting in their own homes, thanks to the transparency of the building, have been able to admire the art. Chipperfield’s new and impressive building continues that democratic tradition with its under-stated elegance and beauty.

Royal Shakespeare and Swan Theatres
Waterside, Stratford upon Avon
Architect: Bennetts Associates Architects • Client: Peter Wilson, Royal Shakespeare Company • Contractor: Mace • Structural Engineer: Buro Happold • Contract Value: £60 m • Date of completion: November 2010 • Gross internal area: 12,000 sq m

The brief called for the retention of Elizabeth Scott’s grade II* listed theatre facade and foyer and the rebuilding of the larger theatre to form a new 1,000 seat thrust-stage auditorium, plus new facilities for actors and audience, all within an urban master plan.

When Scott designed her theatre - art deco and cinema were twin design beacons. The former has left a number of rooms which have been lovingly restored and sympathetically fitted. The influence of the latter led to a wide fan-shape auditorium which murdered the actors’ voices. That has gone utterly. Bennett's, however, retained the rear wall and this move has produced a highly successful part of the scheme: the carefully crafted spaces in the voids between the back wall of the old theatre and the back wall of the new theatre, which are used for projection and circulation. A small row of seats remains in place attached to the retained wall to show just how far from the stage the back seats used to be: 27 metres compared with 15 today.

The new thrust stage auditorium has a good feel to it. It is robust, even rough. It has a Globe-like feel and an exciting atmosphere. It is historic in its references, contemporary in its design. The acoustics are superb. This is a good working theatre, not a precious one.

The newly-designed tower works both as marker and viewing platform in a flat, low-lying town and attracts new visitors into the theatre building. But it too makes a historic reference. The old Victorian theatre featured a tower of identical height whose purpose was not viewing but fire-fighting. Sadly the massive head-tank it contained did not stop the fire that destroyed most of the building and led to Scott’s flawed masterpiece.

One local told the judges, 'I love the stripped-backness of it and I love the idea of reusing so many of the materials of the old theatre. They’ve recycled the boards trodden by Gielgud, Oliver and Richardson in the foyers, you can almost see the blood, the sweat and the tears that went into those old productions.'

The Velodrome
Olympic Park, London
Architect: Hopkins Architects Partnership • Client: The Olympic Delivery Authority • Contractor: ISG • Services Engineer: BDSP • Contract Value: Confidential • Date of completion: January 2011 • Gross internal area: 21,700 sq m

Quietly located to the north of the rapidly emerging Olympic masterplan, the Velodrome exudes an aura of elegance and simplicity. The very form of the building signals the track itself, a continuous, sinuous form that seems to pre-empt and explain the movement of the event itself.

The building is made of three elements, the roof, the concourse and the plinth. The glazed concourse separates the curve of the larch-clad roof soffit and the concrete and landscaping of the plinth. The plinth contains all the service spaces and the normal legacy entrance. In games mode the lower ground areas will also house concession and hospitality facilities. The stairs and movement from the plinth to the concourse and the arena is modest and low key, the drama of the upper space is firmly guarded. In legacy mode the concourse will support cafe facilities that will relate to the south, the landscape and the various other cycling trails that form an important part of the landscape approach.

Internally the material palette is extremely well controlled, fine in-situ concrete abounds. The material and visual emphasis is on the beauty and colour of the timber track, a surface that is constantly and lovingly vacuumed and cleaned.

The cable net roof seems to hang in space detached from the ground by the glazed concourse. While the roof is a significant engineering achievement – it is turned through 90 degrees from the track from which it takes its shape, sits low over the bowl, adding drama and focus to the event itself. The arena is an extremely intimate space, given the seating capacity of 6000. No seat is very far away from the track, indeed in places spectators are literally within touching distance of their heroes.

The building is a consummate exercise in a simple idea, beautifully and efficiently carried out. It is a both an enormous credit to the client and the design team that the effect is one of effortlessness and grace. The plan is an exercise in clarity of purpose and rigorous resolution while the form is quite simply, memorable.