Middlemore Hospital in south Auckland has identified another of its buildings as earthquake-prone.
The multi-storey Esme Green building, which contains offices, is rated at 25 percent of the new building standard (NBS) because two supporting walls are too weak.
A seismic assessment by engineers Beca said the shear wall elements had a disproportionate impact on the seismic rating because of their importance in maintaining support to the floors and lateral stability of the building.
Counties Manukau District Health Board is looking into how to strengthen the Esme Green building to above the quake-prone threshold of 34 percent NBS.
Beca said trying to get it to the key 67 percent level, below which a building is still rated a quake risk, would be very costly.
The engineers have also identified a plantroom containing crucial services at Pukekohe Hospital as quake-prone at 30 percent NBS.
"The structure has some particularly undesirable structural features, including unreinforced masonry infill frames, which have performed poorly in recent earthquakes," Beca documents said. "It has a low life-safety risk, however its failure may have consequences on the operational continuity of the main hospital post-earthquake."
The engineers recommended strengthening the plantroom to above 67 percent NBS, which would be moderately expensive and cause moderate disruption.
Counties Manukau DHB has not made a final decision.
Late last month the DHB confirmed Franklin Memorial Hospital in Waiuku was quake-prone, at 30 percent NBS.
The engineers said it had "critical deficiencies" and cited the extensive use of unreinforced masonry for load bearing walls and chimneys.
The DHB said it was "considering all the possible options which include full strengthening, to disposing of the building and land and re-locating service".
In total, 22 Counties Manukau DHB buildings have had initial seismic assessments. Three were rated as quake-prone, nine as quake-risk (34-67 percent NBS) and 10 were above the key 67 percent NBS level.
These do not include the Galbraith building, housing gynaecology and maternity units, which is just 20 percent NBS. The DHB has decided to replace it rather than strengthen it.
The Auckland region is classed as a low seismic risk area and the due date to identify earthquake-prone buildings is 2032.