Protecting a Landmark Architectural Building in Whanganui

Protecting a Landmark: Te Whare o Rehua Sarjeant Gallery, Whanganui

Equus Industries supplied key waterproofing and roofing solutions for the redevelopment of the Sarjeant Gallery – a landmark architectural building in Whanganui.

Home to a permanent collection of more than 8,300 artworks, the gallery is an important cultural hub. Its revitalisation, led by Warren and Mahoney, involved seismic strengthening, new structural elements, an extension, and redevelopment of the existing basement.

Warm Roof Solution

For both the historic building and the new extension, Warren and Mahoney specified the Soprema DUOTHERM Warm Roof System. With a proven service history, the DUOTHERM system offers engineered thermal performance, condensation risk analysis (CRA) support, and wind uplift studies.

The two-layer, 6.5mm-thick waterproofing membrane is applied over thermal insulation and a vapour barrier, providing continuous and efficient thermal resistance in line with NZBC Clause H1.

• Durability: 35 years in New Zealand conditions with minimal maintenance.
• Sustainability: At end-of-life, a new cap sheet can be installed over the existing system, extending service life by 20+ years without full replacement.

Underground Tanking Systems

Waterproofing of the gallery’s new basement storage areas – critical for housing precious artworks – was achieved with Equus Industries’ Soprema underground tanking systems.

• Torch-applied reinforced membrane: Installed to retaining walls, below slabs, and blind-side applications, forming a watertight bond with concrete to prevent water ingress.
• Soprema COLPHENE 3000: A flexible, self-adhesive SBS-modified bitumen membrane, used on the truck dock retaining walls and areas requiring detailing around complex contours.

Collaboration

Equus worked closely with Warren and Mahoney, main contractor McMillan & Lockwood, and certified applicators Allan Tong Ltd to ensure long-term durability and water-tightness across this landmark redevelopment.

Products supplied:

• Soprema DUOTHERM Warm Roof System
• Soprema Underground Tanking Systems (torch-on and COLPHENE 3000)
• Chevaline Dexx reinforced liquid membrane (dome protection)

Restoration included seismic strengthening, new structural elements, an extension, and basement redevelopment.

Equus Soprema DUO system: 35-year durability with minimal maintenance.

Equus Soprema underground tanking applied to gallery basement retaining walls.

Main Contractor: McMillan and Lockwood

Applicator: Allan Tong Ltd

Architect: Warren and Mahoney Wellington