The transition from adorable bouncing baby to that of a strong independent young adult seems to happen overnight for many parents. Before you know it, instead of tripping over toys you're tripping over CD collections and the occasional friend who didn't quite make it home the previous night.

They're still your cherished offspring, only a lot bigger and much louder and the mess they make isn't so rose-tinted anymore, so what do you do with them? Sunniva Fitzpatrick, violinist with the RT╔ Concert Orchestra and Gear≤id Grant, music teacher and conductor, found the perfect solution for their two children, S∅ofra (21) and R≤nβ(25) when, two years ago, they moved them into a place of their own - right next door.

At an age when they were considering the options of either renting an apartment or sharing a house, it seemed a logical step to consider building a self-contained house next door. "We didn't want them moving away," says Gear≤id. "We had this space we could use and we still wanted them with us but without the usual family friction, now we have the closeness without the rows."

While the idea of sharing a house with your brother might not appeal to everyone, S∅ofra and R≤nβhad always been very close as children and so the transition was easy for them. "Now we're the envy of our friends because we have a house of our own and it's become the central meeting place," S∅ofra says. "We also get to see our parents all the time, so it's the best of both worlds."

Situated at the end of a terrace of period houses off the South Circular Road which date from 1876, they were fortunate to have a side garden which meant that they had the room to build. " It was a space we never used; there were four trees there but the grass never grew properly. Even when the children were small they didn't use it, so it was the natural thing to do," Sunniva explains.

From the outside it would be difficult to spot the new building as the couple were at pains to make it blend in with the old structure and the overall look of the street, so much so that they had to import special bricks from Sweden to complete the detail over the bay window, particular to the era. Ivy from the original house has now spread onto the new structure and completed the "been-there-forever" look.

The idea was to let the children have their complete independence so they have a private entrance to the side of the house which leads them into the decked garden they share with their parents.

Facing on to this area is their new home, where they have their own key, own telephone line - very important - fully equipped kitchen with hob, microwave, washing machine and sound-proofing throughout.

Downstairs is all open-plan, a bright airy space with spot-lighting and varnished wooden floors. A very important aspect when planning the living space for the children was storage - and lots of it - so the design incorporates this.

The two big kitchen counters that double as an eating area give no indication of their capacity for storage when you walk into the house, but from the opposite side they afford a multitude of shelving. Similarly, the seating built into the bay window is all hinged and lifts up to create a handy spot to fire things into for a quick tidy.

A spiral staircase leads upstairs to the two bedrooms and separate shower room. Here the children chose their own designs for wardrobe space; R≤nβopted for open-plan storage whereas S∅ofra went for the opposite and has built-in units. Both rooms have built-in double beds and skylights plus a study area.

"The only disadvantage is the fact that now we have double the bills for everything: double ESB, double telephone, double this, double that" jokes Gear≤id. Now, he hopes, the finances may change as both children have recently finished university.

The couple estimate that the cost of the venture has been only a third of what they would expect to pay if they had bought an apartment instead of building next door.

It has also given their children the opportunity to live away from home which will help them understand the give and take and commitment of forging a relationship, their parents believe.

A thoroughly modern design incorporated into a thoroughly period house has had the desired result, Gearoid feels. "Ultimately, it means that you get to have your family longer than you would normally; it suits them, it suits us, we know they're safe and we know their friends.