Silverstream Landfill Staff Facility
New Zealand's First Certified Commercial Energy Efficient Building
A building designed to lead by example
Commercial buildings account for nearly ten per cent of New Zealand’s annual energy use, and many people spend a large part of their lives inside them. Improving how these spaces perform has a direct impact on energy consumption, comfort, health and long-term operational cost.
The Silverstream Landfill staff facility was designed to demonstrate what is possible when performance is prioritised from the outset. Built for Hutt City Council, this project became New Zealand’s first commercial building to receive the Low Energy Building certification from the Passive House Institute Germany, setting a new standard for energy-efficient commercial construction.
The brief and the challenge
The client required a durable, high-quality building with very low energy demand, excellent acoustic performance and long-term reliability. The facility needed to operate comfortably in a noisy external environment while providing a stable, healthy workplace for staff.
Although the building footprint was simple, the small total floor area of 115 square metres resulted in a very high form factor. This increased potential heat loss and demanded significantly higher insulation and airtightness levels than typical commercial offices. Achieving the performance targets required a construction system capable of delivering both structural strength and thermal continuity.
The solution: performance-driven construction
Izodom ICF technology was selected based on quality and the proven performance of the construction system. Early in the design process, the team proposed targeting Passive House certification to provide independent verification of building performance. Since the selected materials were already closely aligned with Passive House principles, the additional cost was minimal.
The client, Hutt City Council, supported this approach, recognising the long-term value of innovation, energy efficiency, and third-party performance assurance.
Structural system and thermal envelope
The building was constructed using an insulated concrete formwork system that combines structural strength with continuous insulation.
Concrete core structure
Izodom wall blocks were assembled and filled with reinforced concrete, creating a solid structural core within the wall system. Reinforcement bars embedded in the concrete provide strength, durability and resistance to both vertical and lateral loads.
Continuous insulation
High performance insulation is integrated on both sides of the concrete core, forming a continuous thermal envelope around the building. This eliminates thermal bridges that typically allow heat to escape in conventional construction.
By maintaining uninterrupted insulation across walls, slab edges and junctions, the building avoids cold spots, prevents condensation and significantly reduces the risk of mould growth.
Foundation slab
The foundation uses an insulated concrete slab system designed to isolate the structure from the ground.
High-density EPS Peripor insulation boards were installed below and around the slab perimeter, with additional insulation above the slab. This reduces heat loss, limits thermal bridging and lowers the amount of concrete required. The result is a warm, stable floor with no cold zones and improved overall energy performance.
Roof construction
The roof structure is timber framed and insulated above an airtightness membrane. This completes the thermal envelope and ensures consistent internal temperatures throughout the year. Careful detailing maintains airtightness and prevents uncontrolled heat loss through the roof assembly.
Energy-efficient windows
To meet Passive House performance requirements, the building was fitted with uPVC triple-glazed windows filled with argon gas. These high-performance units significantly reduce heat loss while allowing natural daylight into the space.
The windows are installed using airtight detailing so they function as part of the continuous building envelope rather than weak points. This eliminates cold surfaces, reduces condensation and improves acoustic performance, which was critical given the surrounding operational environment.
Mechanical heat recovery ventilation for healthy indoor air
Fresh air is supplied through a Zehnder mechanical heat recovery ventilation system. This system continuously replaces stale indoor air with filtered fresh air while recovering heat that would otherwise be lost.
The result is excellent indoor air quality without drafts or temperature fluctuations. Humidity is controlled, condensation risk is reduced and occupants benefit from a consistently healthy and comfortable internal environment with minimal energy use.
Measured performance
The building achieved outstanding thermal performance across all elements.
Foundation slab insulation - R Value 11 External wall insulation – R Value 3.6 Heating Demand 17 kWh/m2/year Heating Load 16 W/m2 Total Floor Area (TFA) 114.8 m2 Form Factor 4.1 Air leakage @ 50Pa 0.7 Primary Energy (PE) demand kWh/m2/year @ 158
The result: a healthier, quieter and more efficient workplace
The completed facility delivers a quiet, warm and stable internal environment despite challenging external conditions. Energy demand is significantly reduced, operational costs are lower and staff benefit from improved comfort, air quality and acoustic performance.
Achieving Low Energy Building certification from the Passive House Institute Germany confirms that the building performs as designed, providing confidence to the client and setting a clear benchmark for future commercial projects.
