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Award winning Bader Ventura is the first government-funded Passive House development of this size, for public housing customers in Australasia, and is an exemplar project in low carbon/energy approaches to better buildings in New Zealand. The development will deliver 18 units, comprising of 12 x 3-bedroom and six x 2-bedroom in 3-storey walk-up apartment buildings.
With this development, Kāinga Ora – Homes and Communities aim to address three primary areas: reduction in energy use and cost for customers; reduction in carbon in building materials and waste; and to lead and support industry change in line with New Zealand’s climate goals, including net zero carbon by 2050.
To help better prepare New Zealand’s construction sector and meet Aotearoa’s climate goals we are committed to sharing our project insights and recommendations with the industry.
2023 awards include: Construction Sector Beacon Awards – Supreme Winner and Auckland Property People awards – Construction Excellence in Sustainability.
Bader Ventura – Passive House Pilot
Key success outcomes
• 8 Homestar v4.1 rating and 7 Homestar v5 rating
• Will achieve MBIE’s draft Building for Climate Change 2035 ‘final’ thermal performance cap 12 years ahead of expectation
• Heating and cooling costing around $1.00 per day
• First housing structure built with Neocrete concrete panels, saving over 14 tonnes of cement and 9 tonnes of carbon, which is the equivalent of the carbon sequested by 170 twenty-year old native trees
• First publicly funded Passive House of its size in Australasia
With a project of this scale, industry-changing goals and the Passive House Standard our engineering experts were faced with an array of complex challenges including: poor ground conditions; complex foundation required due to the site; the use of concrete; the inclusion of balconies and breezeways; as well as off-site construction.
Poor ground conditions
Extremely weak soil conditions were found on-site, making it unfit for a three-storey building, without an expensive pile foundation.
Instead of an expensive pile foundation, we designed innovative ground improvement, comprising of stone columns with reinforced gravel rafts which stabilises the soils and improves ground conditions.
If we were undertaking the design on a similar site we would recommend Stone Column Ground Improvement, as it achieves significantly increased capacity for support loads, and is also a cost-effective solution. In fact, we have delivered several designs for larger developments in the Auckland region with this method.
The foundation design needed to accommodate a high flood plain level, avoid surcharge onto existing underground services, and be cost effective.
Our stone column ground improvement meant we were able to utilise shallow reinforced concrete foundations, with this opening up further opportunities.
Precision Construction challenged us on how to eliminate all the potential foundation formwork and increase the construction efficiency. From this, the idea of a precast reinforced concrete foundations for Bader Ventura was born. This foundation type is relatively common in Europe and North America for industrial buildings, and lesser so in New Zealand, with this project being among the first apartment complexes in the country with precast reinforced concrete foundations. These foundations have many benefits including, off-site manufacturing, speed and precision of construction, as well as their high quality. The use of this foundation system minimised deep excavations and export/import of materials from and to the site, reducing cost, while meeting the above requirements.
Widely used throughout New Zealand construction, reinforced precast concrete has many advantages such as off-site manufacturing, its strength versatility, fire resistance, seismic resistance and ease of construction. While concrete has many construction and performance benefits, when designing to the Passive House standard it represents an exciting challenge in the New Zealand climate. This is due to its low R-value, as well as the presence of thermal bridging, ventilation and the strict Internal Surface Temperature requirements of the Passive House standard.
Insulated Concrete Panels are the most appropriate wall system for the project as they counter all the above concerns, while assisting with the speed of construction and providing quality structural support in a cost effective and durable manner. To help meet Kāinga Ora’s carbon related goal, Neocrete was used. This innovative product reduces the cement content and therefore the carbon footprint of a project. Bader Ventura is one of the first residential structures to use Neocrete concrete and benefit from its increased strength and accelerated setting time while also limiting the project’s carbon footprint. Over 14 tonnes of cement and 9 tonnes of carbon were saved, which is the equivalent of the carbon sequested by 170 twenty-year old native trees.
Balconies and breezeways
Originally intended as exposed timber, the free-standing balconies were a hidden challenge. Due to the durability of the timber element, it was decided that all balconies would be precast concrete. The Passive House standard requires that no thermal bridges occur between the interior and exterior, and is very strict on the interior surface temperatures. However, adequate connections between balconies and the rest of the building are structurally required and we were unable to use thermally broken proprietary connectors due to the high thermal conductivity of the steel rods.
The breezeways required numerous structural connections between the structural steel supporting stairs and the thermal building envelope, with each connection potentially reducing the efficiency of the thermally isolated panels. Therefore, we needed to find solutions for both the balconies and breezeways.
We significantly reduced the number of connectors in the balconies, and adopted castellation to minimise the number of reinforcing bars. The concrete frames were also reinforced with structural steel, this solution was done through LOD400 detailing ensuring high quality design.
Thermally broken connection to the structural walls was used for the breezeways, minimising the impact on interior surface temperature and reducing thermal bridging. Low conductivity thermal break materials within the connection between the structural steels and concrete walls were also used to limit thermal loss.
Off-site manufacturing is changing how our buildings are delivered today and requires high quality documentation, which is only possible possible with effective coordination between the architectural, mechanical and structural models. Every detail must match up perfectly, including foundation stitched reinforcing; reinforcing starters between precast foundations and wall panels; precast balcony starters to building, structural steelwork and panels and even façade architectural patterns need to lining up.
BIM modelling and coordination was utilised and was key to the successful construction eliminating delay, rework, and additional construction cost. BIM and out LOD400 modelling and deliverables allowed the contractor to price the project construction accurately and effectively, by knowing all quantities including volumes; lifting requirements, propping requirements; construction sequencing and required resources at the building consent stage.
We worked closely with the contractor and fabricator, always having an open line of communication. This meant that on-site, the manufactured properties fitted into place ensuring streamlined construction.
• With Neocrete and clever engineering, precast concrete construction and insulated concrete panels are a great method of building. Together this resulted in quality structures with strong thermal properties, meeting the Passive House standard, all while having a significantly reduced effect on the environment. The use of Neocrete concrete saved the equivalent of carbon sequestered by 162 native trees grown for 20 years. We need to continue to be early adopters of innovative and sustainable focused products and solutions to better construction in New Zealand, and be ahead of the industry changes.
• The use of BIM, fabrication modelling and construction documentation (LOD400) delivery during the design phase was crucial in creating a problematic free design during the construction/instalment phase of the development.
• Thinking outside the box, by providing different geotechnical and foundation systems and solutions resulted in reduced cost, and created further opportunities for innovative, quality, and cost-savings throughout the development. Engineers need to continue to look for better ways and to draw inspiration and knowledge from others, whether this be throughout New Zealand or from overseas innovation.