The parlous state of verandas was uncovered during a $1.5 million investigation into the earthquake-proof state of Auckland's buildings.
Council inspectors have contacted about 800 owners of buildings, asking them to strengthen rusting and poorly maintained balconies.
"Unless they are maintained they have the potential to fall down," de Leur said. "It's often not visible from the outside."
De Leur, in charge of bringing Auckland's buildings into line with post-Christchurch earthquake laws, said most owners had responded to the requests.
Cameron Brewer, of the Auckland Council, said absentee owners often allowed their buildings to fall into disrepair.
"It is hard to motivate landlords, particularly when so many are based overseas and run by trusts and lawyers that hide behind PO boxes."