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Unlike bomb-damaged goods sold off cheaply, the buildings shattered by terrorists four years ago in central Manchester have come back with their retail potential greatly enhanced. Last month, another grand old Manchester institution damaged by the bomb was reborn – as an upmarket shopping centre. The former Corn Exchange has been transformed into a 23 225 m² mall at a cost of £28m and renamed the Triangle.

Standing next to the new Marks & Spencer department store, the transformed Corn Exchange has all the attributes of a new-build shopping centre. All the chic fashion chains, bistros and bars – including Terence Conran's Zinc Bar – cluster around a top-lit, three-storey atrium. The glitzy decor by local architect Ratcliff Partnership features polished stainless-steel handrails, frameless glazed panels and inlaid polished limestone floors, as well as fibre-optic pin-point lights to add a touch of glitz in the evenings.

But all is not quite what you would expect. Inside the main entrance and amid the frenetic shop-till-you-drop throngs stand small hushed groups of visitors. They have been transfixed by the one spectacularly unexpected feature in this stereotypical scene of late 20th-century retail architecture. That is the central atrium itself.

The atrium is a vast triangular volume radiant in daylight. The mountainous roof that spans the volume is nearly entirely glazed, amounting to a total glass area of 1700 m2. Patent glazing panels make up the central circular dome and a large triangular pitched roof that encircles it, while beyond the supporting arcade the patent glazing continues in wide, curving lean-to roofs, plus three slightly smaller domes in each corner.

In any new-build shopping centre, such a vast, glazed dome would have been value-engineered by its property developer to quarter its size. At the Triangle, it is the legacy of the grade II-listed building's former use, when the dome provided daylight for market stalls on the ground-floor trading area. Erected between 1897 and 1903, the Corn Exchange was developed as the foodstuffs counterpart to the even grander cotton trading hall of the Royal Exchange three blocks to the west, which since 1976 has enclosed the spacecraft-like Royal Exchange Theatre.

According to Ray Bunting, director of Ratcliff Partnership, the century-old dome needed little alteration to convert it to its new use. All the glass had, of course, been shattered in the blast, but the supporting ribs of riveted steel plate escaped without structural damage. The only major change to the atrium roof has been to add a small dome in one of the three corners where none existed before.

Less successful are the minor alterations to the dome. The ornamentation and capitals of the columns and the mouldings to the arches and the cornice above them have all been stripped away. Although nothing special, these mouldings were an integral part of the classical design, and their removal leaves an ambiguity over what is new and old. Considering how much effort has gone into restoring the rest of the Victorian building, it is a pity that its greatest asset has been left in an unsatisfactory condition.

Beyond the central dome, the triangular building as a whole has been radically altered to increase the amount of retail space by 70%, while conserving the shell. The original timber trading floor on the ground level has been removed, opening up the basement for a floor of shops sharing the central volume. Likewise, a new first floor of shops has been added behind the original arcades. Two sets of escalators and a hydraulic lift sheathed in frameless glazing have been installed to link the three floors of shops.

In the original building, the market hall beneath the glazed roof was encircled on three sides by strips of offices. Now, the new retail units stretch through these perimeter strips to the external walls, giving them shopfronts facing both the atrium and the outside pavements. However, on the upper floors above the retail units, the perimeter strips revert to their original office use, and these have been opened up by removing their central corridors. The offices are reached by their own street entrances and staircases.

As well as providing a smart new venue for Manchester's shopaholics, the refurbished Corn Exchange provides a vital link in the regeneration of the down-at-heel eastern end of the city centre.