Conversing with the past: in what are likely to be his last architectural works, Norwegian master Sverre Fehn adds to Oslo's physical and cultural history in two projects that engage in different ways with existing buildings. Peter Davey analyses the remodelling and extension of Norway's National Museum of Art, Architecture & Design and refurbished office for publisher Gyldendal.

THE NATIONAL MUSEUM OF ART, ARCHITECTURE & DESIGN, OSLO, NORWAY

Below the Akershus Fortress, on gently sloping ground near Oslo's eastern harbour, is the oldest part of the city, laid out in the 17th century by Christian IV, king of Denmark and Norway, after the original settlement completely burned down. On the whole, the area has not been treated well by subsequent generations. Stodgy commercial buildings have largely replaced the original two-storey brick-and-timber ones, and the quarter is only gradually beginning to benefit from Norway's great wealth.

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One result of the new prosperity is a remarkable series of buildings for the arts, of which the largest and most dramatic is Snohetta's opera house in the harbour (AR June 2008). A much smaller one is the National Museum's architecture building, almost in the shadow of the castle. Built in 1830 by Christian Heinrich Grosch, it was originally the headquarters of the Central Bank of Norway: an exercise in neo-classicism with a porch framed by two giant Tuscan columns in antis. In 1911, the building was adapted by H. Bucher to house the national archives, with a new wing at the back for the documents. Now, the original complex has been restored and converted by Pritzker Prize-winner Sverre Fehn, who has added a generous new gallery for temporary exhibitions.

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Fehn's approach to dealing with the old building is radically different to the one he adopted for publisher Gyldendal's city-centre headquarters in 2007 (p71). The bank building is very carefully restored both inside and out; its spaces, having been used as archive storage, were easily converted to museum use, and the Bucher wing now contains the museum's permanent collections. Fehn's gallery is a completely new element: a square pavilion inserted between the Grosch building and the archive wing. The glazed square is partly surrounded by a concrete wall, 2.5m from the glass. Battered grey in-situ concrete echoes the granite off-vertical counterscarp of the Renaissance fortifications at nearby Akershus.

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Like the counterscarp, this outer wall is intended as a security device. It protects the glass box from human interference and its contents from degeneration by exposure to too much daylight. To prevent the box becoming claustrophobic, parts of the concrete wall are peeled back to allow glimpses of the surrounding city (these gaps in the perimeter are secured with inconspicuous sheets of toughened glass). To reduce glare, the sky's light is modified in the upper part of the pavilion, where it pokes above the concrete (unshaded by the original complex) using horizontal louvres of translucent glass, fixed between the external structural glass mullions of the transparent wall. Externally, the delicate louvres terminate the building against the skyline, modifying what might otherwise seem bunker-like.

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The pavilion is reached via Grosch's museum porch and hall, a mysterious barrel-vaulted cavern with glossy dark green walls articulated in an ashlar pattern, enlivened by encaustic floor tiles and passages of gold mosaic on the stairs. After winding through the heavy piers of his vaulted hall, which houses the reception desk, bookshop and cafe, you emerge into the complete contrast of the pavilion's luminance. Instead of Grosch's low, groined vaults, the lightweight concrete roof of the pavilion is carried on four columns and hovers over the space like a Soanian shallow dome. The floating effect is enhanced by the roof-to-wall detail: the glass skin is 250mm away from the edge of the concrete and the top of this gap is sealed in glass, providing a continuous luminous slot which is echoed at ground level by a continuous perimeter grille, blowing warm air up the glass (the extract is at the top of the columns, which double as ducts).

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Materials and craftsmanship are carefully controlled. Floor and grilles are both of oak joinery work, the concrete roof is perfectly cast and the transparency of the glass is modified with foils. Fehn has always been fascinated by horizons and here, the outer concrete wall provides an artificial one. The strip of sky above it is filtered by the louvres while cool, neutral light is reflected through the glass from the surrounding grey concrete walls (light can be further modified by translucent curtains). Displays can be horizontal on tables or vertical on bespoke white screens that echo the concrete wall. The screens are light and designed to be moved; brought up by hoist from a store in the basement, they are arranged to suit the contents of each exhibition.

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Nothing could be more flexible, more flexible, nor more different from the old building. Yet the two work together to create a remarkably stimulating little museum. It is probably Fehn's last work and, appropriately, perfectly demonstrates his lifelong belief that 'only by manifesting the new can one engage history in conversation.'

Architect

Sverre Fehn, Oslo, Norway

Project architect

Martin Dietrichson

Photographs

Nils Petter Dahle

Nos 4. 5 by Candida Hofer