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Life-changing: Lucy Walker still needs surgery. Photo: Ella Rubeli

A balcony that collapsed and sent 11 people crashing onto a concrete driveway, leaving a young mother with ongoing injuries more than a year later, was held on by 14 nails and had never been bolted to the house.

The revelations have highlighted the poor state of residential balconies in Australia and come a week after the death of three-month-old Aiden Sankey, who plunged six metres when a panel of metal sheeting gave way on a central coast balcony.

Lucy Walker, 32, is still undergoing rehabilitative surgery after fracturing her pelvis, feet, fingers, wrists and arms in the horrific incident during a family get-together in February 2013.

Five brothers, their parents, girlfriends and extended family had gathered at the duplex home to farewell Ms Walker, her husband, Nick Bangs, and their baby son, Billy, before they headed to China.

After finishing dinner on the back deck, they were clearing plates and enjoying tea and coffee when the timber balcony suddenly cracked and collapsed, causing the group to fall more than six metres and furniture to smash on them.

Paramedics worked through the chaos as though it was a bomb scene, using red and green tags to separate those who could walk from those who were seriously injured.

''It was like a war zone,'' Mr Bangs said last year. ''I remember looking to my right and Dad had blood all over him, and a mouthful of grass. I looked down and [my brother] Ed was standing up with blood pouring from his head.''

The builder, Addbuild Master Builders, has agreed to pay for remedial work after a building inspection report revealed the balcony was held on by just 14 ''temporary'' nails.

The family is suing for physical and psychological injuries that lawyer Robyn Burgess said ''will affect them for the rest of their lives''.

One in eight balconies in Australia has maintenance issues that could cause injury, warned Robert Caulfield, director of Homesafe Group.

The figure came from inspections carried out by advisory service Archicentre and issues ranged from handrail failure to serious risk of collapse. Mr Caulfield said the most common problem was rotting timber.

''A balcony by nature is a fairly flimsy structure … it doesn't take a lot of deterioration before they become dangerous,'' he said.

David Hallett, general manager of Archicentre, said poor maintenance of balconies was just as much of a problem as dodgy construction.

The ACT is the only state or territory to mandate compulsory building inspections when a property changes hands. ''Most people are diligent with cleaning gutters annually and checking smoke alarm batteries and they need to make a deck or balcony inspection part of those home maintenance regimes,'' he said.

Police are investigating the structure of the ageing Niagara Park rental property where Aiden died last Sunday. Superintendent Glenn Trayhurn said police were looking at whether Aiden's mother, Colleen McKeon, was leaning on the balcony's iron fencing when it gave way.