Protecting a landmark architectural building in Whanganui

A permanent collection of over 8,300 artworks of significance, spanning 400 years of international and New Zealand art history, lives at Sarjeant Gallery in the heart of Whanganui. The building also hosts an ongoing programme of exhibitions and events – forming an important cultural hub for the community. 

With its revitalisation almost 30 years in the making, the gallery closed to the public in 2014 and public funding secured in 2019. Led by architecture firm Warren and Mahoney, the journey commenced to restore the historic building with seismic strengthening, new structural elements, an extension, and the redevelopment of the existing basement.

“We have an extensive service history with the DUOTHERM system; Warren and Mahoney are very familiar with the system and have specified it on a number of their projects,” says Emma.

“The technical support we have from Soprema is exceptional. When it comes to providing a condensation risk analysis, otherwise known as a CRA, the architects will tell us what R-value they require for their building, and then Equus and Soprema specifically engineer a system to suit that requirement. It’s an engineered system that’s been fully tested. We can perform a wind uplift study as well.”

The lightweight thermal roofing system consists of a two-layer, 6.5mm-thick waterproofing membrane that’s applied over a thermal insulation board and a vapour barrier. A warm roof system guarantees continuous and efficient thermal resistance (R-value) as per the H1 clause in the New Zealand Building Code and is designed for use on exposed flat roofs and decks. 

For specifiers looking for a long-term, sustainable option, this superior waterproofing membrane system is a top choice. 

“This is a system that doesn’t have to be replaced,” says Emma. “Our Equus Soprema DUO system is considered to have a durability of 35 years in New Zealand, with minimal maintenance required. While there are many roof systems that need to be dismantled and replaced at their end of life, the DUO system has what’s called a cap sheet that can be installed over the existing system, which will then provide another 20 years plus durability, without the system having to be removed.”

Another benefit of the DUOTHERM system is its design flexibility – a point of difference that makes it well-suited to large-scale projects such as this. 

Equus Industries’ Soprema underground tanking system was specified for the basement, a crucial part of the project as it’s a storage area for many precious artworks.

Torch-applied to the retaining walls of the gallery’s storage basement, the high-performance tanking system is fully reinforced for underground, below slab horizontal, and vertical external blind side waterproofing applications. The upper surface of the membrane is coated with crystals that specifically adhere to the concrete slab when freshly poured against the membrane, with this adhesion creating a watertight bond that prevents water infiltration to the concrete.  

“The tanking on the lift pits was also done in the torch-on membrane, where it becomes an important part of the substructure of the building. And finally, our self-adhesive tanking membrane, Soprema COLPHENE 3000, was used on the retaining walls of the truck dock entering the basement,” shares Emma. 

This product is composed of SBS-modified bitumen. It is extremely flexible, easy to handle, and fits easily around the sharp contours and angles of concrete footings and foundations.

With the design of the gallery carefully curated to reflect the culture and rich history of Whanganui, Equus Industries has played a vital role in ensuring the water-tightness of the building and the safety of its invaluable artifacts – a project that Emma and her team at Equus Industries credits to the collaborative efforts of all involved, including Warren and Mahoney, McMillan & Lockwood (the main contractor), and Allan Tong Ltd (the team of certified applicators).

Explore more projects Equus Industries has been involved in, and the full range of coating and waterproofing materials for all types of construction.