The owners wanted an extension - so architect Peter Cully transformed their house and a long back garden. Emma Cullinanreports

The owner of this Dublin house had some friends around for lunch one day - in her new extension - and by the time the meal had ended everyone had shifted places until they were all lined up along one side of the table facing the garden.

This new construction, of two garden rooms facing each other across a courtyard and pond, has that effect. It has a dynamism and warmth, achieved through various materials and changing levels, all pulled together into a considered whole.

It is not only people-friendly, it also welcomes wildlife who are oblivious to humans watching them through the glass. The owner had tidied up for my visit and the birdbaths were removed for sweeping but during our conversation these had to be put back as feathered divebombers sought out their aqua targets. "Their expectation has to be rewarded," says the owner, as a bird splashes head first into a bowl.

The brief, to architect Peter Cully, was to have a place to sit out. He praises the fact that the clients drew up a wish list. "In that they did the perfect thing but they didn't say how they wanted to do it which is what an architect wants, not be told how to do the job from day one."

While the extension and the pavilion, which reflect each other's shapes, materials and details across the long pond, are simple structures in themselves they are part of a more complex whole.

"Reconfiguring the entire site was what it was all about," says Cully. "The first impression was of a long, wet, dark garden. People are often impressed by a large garden and yet if you saw a long room like that in a house you would hate it. Now, even though the garden is much smaller, the proportion is a lot happier."

Hidden behind the garden pavilion is a garage in which to store the couple's vast array of sporting equipment, including bicycles and boats, plus three handsome classic motorbikes. Much of this moved from inside the two-up, two-down 1930s house where the clutter was overwhelming. Although there was an existing extension it shared the current extension's footprint with a coal shed and the window to the south was tiny. So, despite having glass doors overlooking the garden, it was very dark.

While the garden was transformed, the interior of the house underwent spatial surgery. Where there was a separate - and small - downstairs loo and bathroom, there is now just the toilet and a utility room. A new bathroom was put in upstairs, overhanging a dead space beside the house. A former airing cupboard that overhung the stairs - and necessitated the two bedroom doors to lie at an awkward 45 degree - was removed.

Downstairs the tiny kitchen was reconfigured and gloss units inserted, from the Panelling Centre: "Ireland's equivalent of Ikea kitchens in terms of price," says Cully.

The client wanted a more traditional kitchen but says that she was prepared to listen to Peter if he produced reasoned arguments. He did convince her but, when she told the builder, Mick Deevy, that she wasn't allowed her kitchen, he said that he could put in any kitchen she liked but that within three years she would regret her decision. She says she now knows that the new kitchen was the right choice.

Both client and architect have high praise for Deevy. "He wouldn't point out a problem until he had come up with a solution," says Cully.

The architect was also happy to take advice from the builder and that came with the decking. "He said that he had laid so much decking in his time and that western red cedar was the best because wood soaks up a lot of water which causes those black marks you see on the ends of timber, whereas water runs off the cedar."

The client was originally nervous about having decking at all, but Cully convinced her that it would work in the overall scheme as part of a mixed palette.

The extension and garden pavilion - known by the owners as Terminal 2 partly because of the inset runway lights that run between the two structures - are steel-frame structures with zinc roofs.

The metal was chosen for its ability to be cut into sharp lines: the crisp roof perimeter being helped by the fact that the high section of roof is inset from the edge.

Cully also likes the colour, for the way in which is almost disappears against overcast skies and because "it reminds me of Parisian rooftops". The downpipes match the roof metal, an indication of basic design care that many housing developments don't bother with, instead opting for plastic downpipes that stand out from with the building's colour.

The house extension roof is held up by columns that are in the standard red they are produced in. "They have to be a bit eccentric because of their placing," says Cully.

Two of them are placed in such a way as to allow the southern corner doors to slide back, eliminating the corner of the building and exposing the room to the outside world. This disappearing corner trick was made famous by Dutch architect Geritt Rietveld in his Schroder house in Utrecht, in 1925. Other examples in Ireland include a house by Richard Murphy Architects just outside Galway city and an extension by Gerry Cahill Architects in Dún Laoghaire.

Another Rietveld reference could be attached to the way in which this house and garden consist of various planes on different levels, building up an overall picture, something perfected by the De Stijl movement of which Reitveld was a member, as was artist Piet Mondrian.

The key is to bring the various elements together in harmony, something achieved in this construction by ordering the elements: for instance, the pond lines up exactly with the southern edges of the two structures. Also, the decking is level with the internal floors so that you can step out and forward before stepping down onto the sandstone terrace.

The placing of the various sections were guided by the sun. The south edge of the garden is always in shade, so this is where the path is, whereas the other side, which gets the midday sun, is a large paved seating area.

The house extension gets the morning sun and the pavilion glows in the evening.

Peter Cully's wife, Janie Lazar, who runs the Design Classics Direct furniture company, visited during the build and became involved in planting up the garden, with cuttings from her own home taking root here. Janie consulted with Celena Kelly who she had met on a City and Guilds horticulture course in Dublin, and she did the planting.

While this project is much tinier, the success of designing a building and garden together can be seen in the Alhambra, the joint projects carried out by Edwin Lutyens and Getrude Jekyll and the Taj Mahal. The latter is never photographed without its pond and garden in front of it.

Architects such as Alvar Aalto - also Dutch - saw a move forward from Modernism in more complex structures, using pathways and in-between spaces to make up a whole that is pleasing to humans. And this scheme shows how places can be people-friendly and add up to more than the sum of its parts.