Design Solutions - Problem: there may be many wonderful things about living in an old building but one of the downsides, particularly with 18th century buildings in Dublin's city centre, is that finding space for contemporary needs - like multiple bathrooms - can be a headache.

And carving up rectangular rooms is rarely successful visually.

Maggie Byrne lives in a long narrow late Georgian building at the foot of North Great Georges Street in Dublin 1. Her husband is architect Dennis Byrne, with whom Maggie works at his offices in the apartment and in the commercial development next door.

Designed by Byrne, this new building won the Architects Association of Ireland Award 2004. The couple bought their home in 1999 and live there with their 14-year-old son Tadgh.

"Dennis is Irish and I'm London-Irish," says Maggie. "When we came back to Dublin about eight years ago, we lived on Dorset Street and used to walk by this place wondering why no one had bought it."

The reason was that the building, that includes a shop at street level and was part disused warehouse, was almost derelict.

But with four storeys, the upper floors have a fantastic outlook over the city. Although it was in bad condition ("the warehouse part hadn't been used in 50 years") it had - as many an optimist has observed - great potential.

"It took about a year just to make it habitable. We made a self-contained flat at the front on the lower floors and kept the shop going at street level to fund things."

The work on the house continues - they have just finished replacing metal windows that were installed after the 1970s bomb on Talbot Street blew out the originals.

Maggie and Denis decided to create their main living spaces on the top floor to take advantage of the views and created bedrooms below.

This top floor includes a roof garden and two livingrooms separated by the kitchen. But the family needed to make more of the long room.

In particular they required more storage space, kitchen space and had to come up with some way to close off the second living area so that it could be used when guests stay. This would need its own shower room.

Solution: a "box" was built to one side of the long space to separate the kitchen and the livingroom at the front of the building. It was made to house many things and facilitates many functions.

"It gives us a utility room-cum-larder with a second sink - where I hide small appliances and the fridge freezer - and also bookshelves and cupboards." On the other side of the box is a second livingroom which can be closed off from the kitchen by a sliding door and used as a guest bedroom. A shower room on that side of the box then serves the bedroom.

The "box" has also given the family extra floor space. Above is a sitting area that is used mostly by Tadgh as a place to hang out with friends.

Reached by a built-in step ladder, for younger visitors it provides lots of fun: "it's like a tree house; kids like to look down on the adults and fire water pistols."

A triangular window lets in south-facing light. The "box" is a success because it doesn't interfere with the original architecture but also, says Maggie "doesn't feel like we've broken up the room - the space on the left is quite wide and doesn't interfere with the flow from one room to the other. It isn't too high or too wide".

Dennis Byrne Architects, 26 North Great Georges Street, Dublin 1

Tel 01 8788535