Norwich Cathedral: An ace caff attached

The building of a £3.5m refectory at Norwich Cathedral called for a design that married modern architecture with the original Norman-cum-Gothic precepts. Jay Merrick admires the result

Delia Smith and her Canaries may have put Norwich in football's top flight, but the city has always been in modern architecture's premiership because of one building, Norman Foster's svelte 1970s art-hangar, the Sainsbury Centre for Visual Arts. Now Norwich can boast another notable essay in modernity - not as obviously important as Foster's, but carried off with a delightfully counterpoised fusion of space and structural detail.

Delia Smith and her Canaries may have put Norwich in football's top flight, but the city has always been in modern architecture's premiership because of one building, Norman Foster's svelte 1970s art-hangar, the Sainsbury Centre for Visual Arts. Now Norwich can boast another notable essay in modernity - not as obviously important as Foster's, but carried off with a delightfully counterpoised fusion of space and structural detail.

The Sainsbury Centre was flash-forward futurism on a tabula rasa site. But the building we're considering is tied in a very particular way to history and should, ideally, be encountered in a way that accentuates the connection. And so, from Norwich station, for argument's sake, the route of choice takes one across the road junction and then down the steps to the river walk along the banks of the Wensum.

Workaday Norwich evaporates. We pass the squat arch of the old riverside goods-landing house; then it's left, up the gentle incline edging the playing fields of Norwich School for boys, and into the lower close of the city's Cathedral of the Holy and Undivided Trinity. There, we slip into palimpsests of the 18th and 19th centuries: walls of flint or darkly choleric brick, unruly swags of Albertine roses, sharply cut cascades of lime-green ivy. We prepare to nod - discreetly - to the passing ghost of Parson Woodforde, the Norfolk diarist obsessed by ice-water baths.

The cathedral appears on the right, and we glimpse something new affixed to the southern range of its cloisters, which, in size, are second only to Salisbury's. There is a dark, horizontal sheen of glass, sets of thick oak louvres and a simple, leaden roof-line. We're looking at the £3.5m cathedral refectory, designed by Hopkins Architects, whose works range from Glyndebourne's auditorium to the brilliantly executed Westminster underground station and the bathetic, over-egged grandeur of the staircase at Manchester Art Gallery.

What can't be sensed immediately is the modernity at the heart of the refectory's design - a modernity, though, dictated by the imperatives of the cathedral's structure, whose essential form is rooted in the 11th century. The best way to appreciate this segue is to approach the refectory via the cathedral nave and the adjoining 14th-century cloisters, famous for their rib vaulting and scores of carved bosses. In these spaces - and most obviously in the long nave - we pick up the obvious signals: clear space, columns, fan-vaulting.

Suitably prepped, we approach the refectory through an angled cut in the wall of the south cloister at ground level, under the deep eaves of the new roof. It's immediately clear that the new building is the servant of the cloisters, and of the library range in particular. The 1m-thick walls of the library - a rubble composed of flint, chunks of brick and limestone - were deemed untouchable, structurally, by the Cathedrals Fabric Commission of England (CFCE). And it was the CFCE that insisted the refectory's design should be based on Norman-cum-Gothic precepts.

Hopkins's solution is a big, two-level, glass-and-wood shoebox, which is only just attached to the old library. The strategy is immediately apparent: there's a gap of about 3 metres between the rubble wall and the oak-boarding of the ground-floor part of the box, which contains the kitchen, lavatories and services. Above, the only thing that links the long edge of the roof with the eaves of the library is a wide gutter. We see what's new, and what's old, with great clarity. Ducting and gutter downpipes have been deftly concealed.

But what's locking the box together and holding up the roof, with its unusually heavy lead covering? (Lead cast by neo-medieval hand in roughly surfaced sheets formed by pouring the molten material on to carefully smoothed trays of sand.) The answer - and the architectural revelation - is waiting upstairs.

Architecture is usually dominated by steel and concrete and crude, rectilinear structural inferences; our reactions to it are too often denatured. We rarely see precisely how a building, or a roof, is held up. In Hopkins's refectory, we not only see it all, but we marvel at how elegantly it's done. The practice prides itself on extrapolating the designs of its buildings from basic structural requirements - and it may never do so with such simple clarity again. The structure is based on a grid of glue-laminated oak columns; those, in turn, sprout four-pronged "trees" of upturned oak struts from steel nodes; and the struts are locked into the wood-faced steel substructure of the roof.

No big deal, in theory. Or it isn't until one grasps just how refined the specifications are. Hopkins and their engineers, Buro Happold, have not only double-tapered the columns and struts; they've pared down their dimensions to what seems an impossible slimness. How can the outer pairs of struts sit at an angle of not much more than 15 degrees from horizontal and transmit roof-loads? It seems amazing the roof can be supported at all.

But it is, and the arrangement is completely engaging. Study the room for a minute or two, and you learn exactly how the structure works. Indeed, it becomes increasingly familiar: is it not a perfectly modern riff on the architecture that can be seen in the nave? Mike Cook, of Buro Happold, may have trembled in the presence of the CFCE's world-renowned academic medievalist Jacques Heymans, of Cambridge, but there's no doubt that he has delivered an excellent technical solution.

In terms of architectural form-making, Andy Barnett, the Hopkins director who shepherded the project from 1995, has something to be proud of. It is likely that the new refectory will have a positive effect on the cathedral's pulling-power, already good enough to attract more than 300,000 visitors a year.

Hopkins Architects are doing rather well in East Anglia. That may partly be because Sir Michael and Lady Hopkins have a second home near Aldeburgh. Hopkins's statement of Anglian intent came two years ago with The Forum, a library and educational complex in the heart of the city - a hefty, horseshoe-shaped bastion with super-thick structural brick walls and a vast, curving glass façade giving on to a stepped plaza. There's no doubt that the building, which has a Pizza Express restaurant on an internal bridge overlooking the plaza at first-floor level, is highly popular. As architecture, though, it feels a little lumpen.

An even tougher challenge awaits the practice in Bury St Edmunds, where it is developing designs for a cultural centre. That is going to be fraught. St Edmundsbury Borough Council has fudged an attempt to convert the Corn Exchange into a mixed-use arts centre. Why were Ushida Findlay Architects asked to deliver a proposal when there wasn't money to drive the project through? Now the council expects Hopkins to revivify the cultural vibe of the sugar-beet-scented Suffolk town with a building on the site of a huge car park above the market and shopping centre.

The architects will no doubt come up with a decent building. But how will they deal with landscaping and the lack of coherent pedestrian connection with the core of Bury? It may be only 150 metres away, but getting there is fiddly. Meticulous, small-scale urban masterplanning is needed.

No such problems by the banks of the Wensum. Here, the modern and the archaic are apparently comfortable bedfellows. Who, though, is the rampant nude blonde in the lubricious portrait by Anthony Dalton? Could the lady be taking tea in the refectory and admiring the elegant jut of the oak struts? Perhaps Mr Dalton should set up his easel here. Architecture like this deserves centrefold treatment.