Work to upgrade Middlemore Hospital's baby unit was under way for a month with no building consent.
Construction had to be urgently halted - and has remained that way - as the hospital battles to find beds for sick babies and children amid a surge of winter viruses.
Auckland Council forced the stop in May when it realised there was no consent in place.
The $5 million project for a desperately needed expansion of the South Auckland hospital's neonatal unit started in April.
Cots in the existing babies' unit had to be moved into the children's wards for construction to take place, meaning there were up to 26 fewer beds than normal.
Then the spike in the respiratory illness RSV hit and a playroom has had to be converted into a space to care for 11 babies.
Doctors and nurses say they are having to make tricky decisions about who can be admitted and who needs to be cared for at home.
RNZ understands many were already frustrated at the April start date for the construction work because it was too close to winter.
They are even more so as they grapple with the large number of admissions while there is no construction work happening which will eventually ease the problem.
Counties Manukau DHB said it was given the wrong advice by an independent contractor who told them a building consent was not needed.
During about a month of work, some demolition took place and the initial wall framing was built.
In a written response to questions from RNZ, a DHB spokesperson said the upgrade to the babies' unit was already designed to the building code standard.
But it had to collate that information to submit to the council to get consent, the spokesperson said.
The DHB did not anticipate such a large spike in winter illnesses because last year had been much quieter because of the lockdown, they said.
But medical staff spoken to by RNZ said it was always likely they would rebound this year.