The Photographers' Gallery: A building that extols the calm virtues of still life

The new Photographers' Gallery reframes how we view images

The Photographers' Gallery, which pulled half a million visitors a year to it famously clunky previous home in Great Newport Street, now occupies an ex-Edwardian rag trade sweatshop in Ramillies Street, at the northern edge of Soho. The £9.2m building, part funded by the Lottery, which has just opened, has been extended vertically by two deep storeys and remodelled internally by the fêted Irish architects, John Tuomey and Sheila O'Donnell. They have produced what might be described as "slow" architecture.

Those who have visited the Glucksman Gallery at University College, Cork, will know what O'Donnell and Tuomey are about. They are profoundly interested in towers and controlled outlooks; they love crafted details; they delight in juxtapositions of tough natural materials; and they know how to create space that feels still. Their buildings have a rather distinct sense of weightiness. No surprise, then, that the Photographers Gallery has a very characteristic sense of materiality and heft.

Its vividly energetic director, Brett Rogers, particularly relishes this aspect of the design. "There are so many images, everywhere," she says. "And the speed of them! People don't take time over images. The Photographers' Gallery is about engaging people with the history of photography. It's about slowing people down."

What takes the architecture of the Photographers' Gallery beyond mere dryness is the way O'Donnell and Tuomey have successfully created quite distinct shifts of interior ambience in different parts of the building.

The architects' interest in towers has produced a singularly striking external feature: a big, north-facing "periscope window" that juts above the raised box of the building's roof.

The revised architectural language of the building's exterior is pretty straightforward. Polished black terrazzo wraps around the corner of the building, announcing its reception and cafe segment; the vertical extension – a three-storey "lift" that contains two high-ceilinged galleries – is signalled by black cladding over the 1910 brickwork; and the public entrance is composed of nicely crafted timber panelling. Externally, the architectural effect is oddly ambiguous: distinct and logically demarcated, but in a very appliquéd way, and not quite producing a satisfying sense of overall composure.

Inside, however, the architecture of the spaces work beautifully. The quality and atmosphere of the two new upper galleries are exceptionally satisfying. These are calm, specifically unfunky spaces, perfectly able to handle big, expressive hangs. The opening shows – three section from Edward Burtynsky's OIL (featuring Extraction and Refinement, Transportation and Motor Culture, and The End of Oil) and the Delhi-based Rags Media Collective's An Afternoon Unregistered on the Richter Scale and 36 Planes of Emotion – will test these rooms.

The upper galleries, and the windowless climate-controlled space for delicate historic photographs, have a stillness that will strongly emphasise what's being exhibited. On the top-floor gallery, the "periscope" brings in abundant north light and views across rooftops.

Another level down, the gallery space gains an angular east light from a small-glazed, appendix-like space at one end of it. A storey lower still, the Eranda Studio, an education room with a brilliantly devised hinged dividing wall, makes do with the building's original, iron-framed windows on two sides.

There is a spacious basement bookshop with a dedicated print-sales room just off it, containing the celebrated works of 37 of the world's greatest photographers.

Brett Rogers knows that she's in control of spaces of great curatorial and viewing quality. But she wants the Photographers' Gallery to be known for more than that. "This has to be seen as a social place, a community," she says. That's why she will ask Westminster Council to allow her to display, or screen, photographic work on the big, blank brick wall leading to the cut at the top of Ramillies Street.