Sainsbury Centre for Visual Arts, University of East Anglia, Norwich

In the idealistic 1960s seven new UK universities promised an educational paradise on earth to baby-boomer students. Disassociating themselves from the gowns-and-gothic of Oxbridge, turning away from the redbrick-and-corduroy of town-based universities, these colleges were new, campus-based and forward-looking.

Modernist architects were employed to create their buildings, integrating teaching and living spaces for faculty and students. One of these new learning centres was the University of East Anglia (UEA), which was in the hands of Denys Lasdun, the English architect who designed the South Bank's National Theatre.

He provided the distinctive ziggurat shape of the student residences, the strongest visual feature at UEA. These are set in a long spinal 'megastructure' configuration across the spreading landscape of Earlham Park facing a flooded gravel pit, tastefully rechristened The Broad.

When, in an extraordinary act of generosity, Robert and Lisa Sainsbury donated their vast and growing collection of art and ethnographic material to UEA, they also indicated that they would give a new building to house their gift. Their collection and the new building, together known as the Sainsbury Centre for Visual Arts (SCVA), would become the nucleus of the School of Fine Art and Music.

The Sainsburys' preferred architect was Norman Foster. Back in the mid-1970s, Foster designed a space-age landmark on the UEA campus, breaking with Lasdun's overall plan. Clad with replaceable silvery aluminium panels, the SCVA seemed a marvellous departure from convention.

It was a way ahead; neither demeaning or detracting from the material it contained, but raising the game for the museum from just being a simple container of objects. Foster created a hangar-like enclosure, among the first of the suavely elegant buildings for which he is now world-famous.

By putting all the necessary structure in the spaceframe walls, he made a vast, uninterrupted and therefore uninflected space for the artefacts. It was big enough to also house the offices and teaching spaces of the academics and students.

In the SCVA, there are no visual distractions, no columns or corridors, just the paintings, sculptures and other items. The first exhibition shown there was about the designers Charles and Ray Eames.

Not only did the eclectic nature of their design work seem a suitable match for the wide range of the Sainsbury collection, but Foster's building is also a direct descendant of the renowned house the Eames built for themselves in 1949 at Pacific Palisades, just north of Los Angeles. The SCVA was flexible, adaptable and responsive to the environment in terms of daylight and temperature.

It is worth noting that the client stuck by its architect, and Foster still has an affection for the building that brought him such fame. The result of this lasting relationship has been several large-scale revisions of the building. The first was in 1987, when the original silver panels were replaced en masse with flat white ones. As Bill Wilson notes in the Norwich section of The Buildings of England, this was 'an unfortunate departure'.

Foster returned in 1989-91 to create the Crescent Wing, which added a new exhibition space, offices and workrooms. He did this by carefully going underneath the frontage of the building, thus skilfully avoiding any major change to his original bold simple structure. All that is visible outside is an elegant strip of window set in the grass in front of the building.

Time passes, collections grow, standards for display and storage change. In 2006 the innocence of the SCVA's wooded setting is gone. Now the trees are interspersed by triffid-like creatures; tall metal towers each topped with a single all-seeing CCTV eye. Despite their listed status, the concrete of Lasdun's terraces is crumbling. Lord Foster's helicopter has returned once more, bringing him to update the SCVA.

Again Foster has achieved the required changes without compromising his original vision. A subterranean delivery point was included when it was first built, unobtrusively sited at the back of the building. As mentioned above, Foster excavated under the front of the structure in 1991. These two basement areas have been consolidated by the simple expedient of excavating down through the floor plate at the very centre of the building.

There is a small photographic display in the shop that shows the growth of the SCVA, from early designs in 1974 to the new building. A photograph of a JCB digger at work inside the space normally occupied by Degas's little ballerina is especially dramatic.

So, what have these latest alterations achieved? More exhibition and education space, larger stores and conservation areas, combined with better public circulation within the building.

Other changes include a new visitor reception where stickers are issued and statistics collected. A large new shop has inevitably been created in the excavated lower level.

And how have the curators used their new spaces? The inaugural exhibition is Pacific Encounters: Art and Divinity in Polynesia 1760-1860, an exploration of the cultural exchanges between navigators from Britain and the islanders of Polynesia. This subject relates well to the Sainsbury collection, which is rich in non-European artefacts.

Pacific Encounters is partly at entrance level and partly in the new and old underground areas. It relies on plenty of temporary structures to enclose the objects, which were borrowed from collections all over Europe. Because the Polynesian artefacts are so enigmatic and powerful, it is a shame that portraits of the Europeans involved in the story are mostly exhibited as photographs.

The lighting seemed remarkably eccentric. There are two whalebone objects next to each other, and when I visited one was well-lit, the other in utter darkness. Why? Did the lamp blow and have health and safety rules made replacement difficult?

The academic part of the SCVA has been renamed the School of World Art and Museology to better reflect fashionable academic disciplines. Outreach for the whole East Anglian community has been added. Local schoolchildren benefit from new education spaces downstairs, one with an amazing Polystyrene Polynesian ceremonial space, made to go with the present exhibition.

Other changes include a new 'shop window' for small changing exhibitions of items from the reserve collection and a refurbished cafe. There is also a new internal public link between the main building and the Crescent Wing extension.

Foster says the original Sainsbury Centre building 'challenged preconceptions about museums'. Today, the centre does not appear as cutting edge as this, but the redevelopment has achieved the aims to create new connections between different parts of the building, improve amenities and make sure the university can meet the demands of the 21st century.

David Brady is a teacher working in London

Project data

Cost: £10m

Main funders: Sainsbury family, University of East Anglia

Exhibition design: George Sexton Associates

Architect: Foster & Partners

Main contractor: Kier Eastern