Wintergardens

In March 2023, the Winter Gardens were fully re-opened to the public following a complex two-year project to seismically upgrade and undertake major repairs and improvements to the glasshouses and wider site. The repairs and strengthening works were complex and required a number of changes to the structures, which have been carried out with the utmost care and attention to detail to ensure that the heritage values of the place have been protected and enhanced. This icon site has been conserved for the future. This has been accomplished on time and within the original estimates on behalf of Auckland Council.

The glasshouse have been brought up to 67% National Building Standard using the designation of IL3 (i.e., the Importance Level). IL3 is the highest standard and is used where the aim is to not only safety of life, but limiting damage as much as practicable to the structures, so that they can still operate after a seismic event. The solution by the structural engineers provided for an elegant system of inserted steel components such as plates, cleats, and tie bars, similar to those of the original steel roof structures, to prevent potential wracking (lateral movement) of the slender steel barrel vaulted roof. The large reinforced, brick-clad concrete pillars that provide support for each main steel truss were assessed as being sufficiently strong enough to resist lateral forces, and therefore did not require any strengthening.

The 2005 high-level toughened glass to the barrel-vaulted roofs no longer complied with the updated New Zealand Code of Practice for Glazing with respect to safety. The Council therefore appointed a specialist glazing engineer to advise on the replacement of the glass and supporting frames so that the steel roof structure and its glazing could be brought fully up to standard. The recommendation was that all glass and glazing bars over 5 m needed to be replaced. The alternative recommendation for a safety net in order to catch falling glass in the event of an earthquake, was considered too intrusive and only a short term solution.

The use of clear glass, rather than the existing obscure pattern introduced during the mid-20th century, has restored the structures closer to their original appearance when first built. This has been one of the most positive outcomes of the project. Visitors and staff can now enjoy a changing backdrop of the sky, which is fully visible, where previously it was concealed from view by the obscure glass.

The chimney to the Tropical House owing to its height and potential for toppling required support utilising a seismic steel frame fitted internally and connected to a new, much deeper pile foundation. The single storey boiler room and potting shed attached to the back of the Tropical House were also strengthened with added steel to the roof structures, and the buildings were re-roofed and repaired.

The glasshouses were in rather poor condition, mainly through water damage inherent in their function, but also because of years of water penetration from an inadequate rainwater disposal system, blocked drainage and the more frequent intense rainfall being experienced. This manifested itself through leaking roofs and over spilling gutters saturating the masonry encouraging plant growth which was causing damage, decaying joinery, cracked and delaminating plaster, corroded steel elements, deteriorated paintwork, and rotting timber display shelving. Twelve additional cast iron rainwater pipes were carefully integrated to each glasshouse to increase the capacity of the system and prevent water penetration in future.

Enhancements have included new lighting inside the glasshouses and in the courtyard and fernery plus new shelving in both house for the displays.