Hutt Hospital's Heretaunga Block. Photo: RNZ / Samuel Rillstone
Hutt Hospital's main block has scored a rating that lifts it out of the earthquake-prone zone, clearing the way for more upgrades.
It was feared the Heretaunga Block and its more than 200 beds would have to close when it was rated quake-prone last year.
It has remained open, and now a new engineering assessment has scored it at 35 percent of New Building Standard or NBS.
Thirty-four percent and under is earthquake-prone.
Te Whatu Ora said safety measures will remain in place, and the block's long term future will be reassessed.
It said upgrades to the maternity ward and special care baby unit can carry on, and now clinical spaces on level one will be upgraded, too.
The vagaries of the earthquake assessment system have been on display at the hospital.
It was rated in 2021 as not earthquake-prone, only to be rerated as prone in 2022, and now rerated again as not prone.
The 2021 rating of over 40 percent NBS accepted by Hutt City Council was based on a 10-year-old seismic assessment that did not take into account lessons from the 2016 Kaikōura quake.
Just a year later, a new assessment rated it just 15 percent NBS, due to the outside concrete panels on the facade. The ground under them was cordoned off.
Engineers have now taken yet another look.
"The latest assessment has found that the precast panels' connections are different to those typically encountered, and required careful consideration by several engineers, including drawing upon international research," Te Whatu Ora said.
This lifted the overall rating to 35 percent, for a building categorised as Importance Level 3 (IL3).
But by some measures, Heretaunga could be categorised as Importance Level 4 (IL4) - of high importance to the community for delivering special post-disaster functions, because it contains the likes of coronary care, maternity and radiology - and doing this would reduce its NBS score.
IL4 should be more resilient than IL3, and ideally hit 67 percent NBS.
A seismic report to Te Whatu Ora last year suggested expanding what counts as an IL4 hospital building.
"Some buildings have been regarded as IL4 when IL3 would have been more appropriate, and vice versa," it said.
RNZ has asked Te Whatu Ora where it has got up to in adopting the 2022 report's recommendations for Importance Level ratings, and filling the many gaps in seismic assessment information.
A low NBS is tied to a particular structural weakness identified by a seismic assessment but does not "point to an immediacy of risk", the 2022 seismic report said.
Building authorities and Te Whatu Ora are keen to point out it is "not a predictor of building failure, nor an assessment of safety in a particular earthquake".
However, a low rating does reflect higher odds of the building being hit by a quake that exceeds its capacity to cope; and the system refers to the "risk to life" being 10 times higher in a 34 percent NBS building versus one at 100 percent.