Architecture: How the need for a dining room becomes a triumph for the spirit of enlightenment

Here are three projects to lift the spirits, particularly spirits trapped in the houses they already occupy: a glass dining room, an extension that takes a house's inside outside and, perhaps most pleasing of all, an idea that turns a bland basement window into a work of art. Not simply a matter of let there be light; also let there be excitement. Nonie Niesewand talks to the architects on site.

An extension to your house built out of glass? The word conservatory comes to mind, closely followed by the names Merchant Ivory. Isn't every glass structure attached to every house you've seen redolent of the past? Too hot or too cold. Too bright or hazed with condensation and dependant on a skeleton of wood or metal.

If that is your idea of heaven, so be it. But there are other possibilities that are more exciting, more practical, more modern. The structure shown here has none of those old conservatory characteristics.

The secret is partly with the architects, but mostly it lies in the glass. Pilkington's K glass is coated in silicone; it doesn't overheat and it has the best UV factor of any glass tough enough to form a facade. Silicone sealing makes joints invisible. And look! No glazing bars!

The Royal Institute of British Architects, in search of potential winners of its Stirling Prize, has chosen a handful of small-scale extensions to town houses. Here are three of them. Interestingly enough, they are all dining rooms - just when you thought kitchens had swallowed them up for ever.

A Glazed dining room extension on a Georgian house

Far from moving somewhere smaller once their five children had grown up and left, architect Cany Ash's parents wanted more dining space for their five children and grandchildren to meet. Their friendly Shaker-style kitchen ended in an L-shape with a large picture window installed in the Seventies, when the place was used as a nursery school.

Rather than close off the pretty garden with its well established cherry tree, Cany Ash and fellow architect Robert Sakula determined to wrap one side of the kitchen with a glazed front extension, sheltered by a cantilevered glass roof. Pilkington K glass, with its silicone joints that obviate the need for glazing bars, gave them scope to shape the conservatory in a very intricate, geometric way.

"Silicone glazing opened a new way of thinking and let us use glass in a skeletal way," says Ash. Each glazed wall panel just slightly alters the angle or lowers the height to join on to the next, like a great glazed caterpillar - all the more remarkable when you consider that glass is straight, flat, hard and cold.

To match the evolutionary path that the extension takes, the giant cantilevered roof above is jointed at different angles like a giant pterodactyl wing. The staggered gradient means that the glass extension goes from the full height of the first-floor landing down to the relatively low garden entrance that matches the height of the remaining picture window. Acid-etched egg shapes on each roof panel cast interesting opaque reflections at night when small halogen up-lighters set in the slate floor beam up at them. Heating runs under the slate floor which extends into the terraced garden in great zig-zags. These simple cut-out shapes help to extend the boundaries beyond the new glass extension and link outside with in.

The Ashes say that sitting in their new extension is like being in the garden which envelopes them. Even better, the heat retained in a typical sheet of double-glazed K glass is equal to that retained in a brick wall. As Cany Ash says: "You're not throwing money through the glass."

Contract Value: pounds 16,000

RIBA jury comments: "... creature-like image of F wings of the roof in glass ... a guillotine of glass slicing through the slate paving ... crafted detailing".

A dark basement dining room sees the light

A new building opposite blocked what little light there was in the basement dining room of a London couple's flat. Rather than live with the lights on all day the owners commissioned the architect Nick Coombe and designer Jonathan Stickland to solve the problem. Caroline Yates, who teaches at Prue Leith's cookery school, identified Stickland as a designer she liked from his set-squared filo pastry cases on her course.

He replaced the original sash window with 10ml toughened plate glass, etched on one side, which spans one metre. It swivels within the pilastered niche, cantilevering above it to shield the pavement grilles or coming down at an angle like a shade to diffuse the light. They dug deep into the plasterwork and angled it interestingly to frame the installation. A single down-lighter halogen beam - which they call the "soup ladle" - highlights the sculpture. Stainless steel spikes protect the toughened glass of the long horizontal window at pavement level. It was difficult to get planning permission but Stickland argued that rights to daylight are not a planning issue.

Contract Value pounds 10,000

RIBA Jury comments: " ... minimal impact on the street ... an example of what can be achieved on a modest scheme through detailed design".

Taking a dining room into the garden

Like every modern architect, Chris Wilkinson dreamed of building his own home from scratch. But the reality and difficulty of finding a site - and then the time to actually build - meant that when the family moved home last year, they bought a Victorian house in Dulwich, South London, and decided to extend the dining space to house their Charles Eames table. Rather than make the distinction between inside and outside too obvious, Wilkinson decided to extend the white-plastered party wall from inside the dining room to the garden wall outside, as well as the sandstone floor. This makes the extension more like a room installation than a patio adjoining a dining room. Pilkington K glass joined with silicone seals practically make the walls disappear.

"Besides," says Wilkinson, "it's got the lowest UV rating." Indoors, a glass panel within the roof has a chamfered frame like a light-box, angled to bring the sky indoors by day. At night it makes a spectacular frame for the fibre-optic sculptures that his sculptor wife, Diane Edmunds, makes. Both of them were inspired by the way in which the American sculptor James Turrell uses structure to capture light. The flat roof is emphasised with a steel joist profile and at one side a piece of architectural ironmongery jutting from the roof has a long chain carrying rainwater down it into a deep channel that demarcates the terrace. Architects' Journal gave Chris Wilkinson their recent cover story for his celebrated public projects, which include the Stratford railway station, where the Jubilee line terminates, as well as the recently opened Stratford Market train shed, the Challenge of Materials gallery at the Science Museum, the South Quay footbridge in Docklands, the Tyne Millennium bridge as well as Science World in Bristol. No wonder Chris Wilkinson calls the dining room extension to his Victorian family home a "very minor project".

Contract Value: pounds 35,000

RIBA jury comments: "... stealthy detailing ... a new and airy relationship between the house and garden ... refinement and restraint".