Dunedin architects who helped design low-carbon houses for a pilot project hope they will one day be the norm.
Architype’s Tim Ross worked with building giant Fletcher Living on the innovative project in Auckland.
The low carbon (LowCO) houses emit seven times less carbon than the standard existing Kiwi home and use half the electricity and water.
Ross said it was exciting to be involved in a project that was changing the direction of building in New Zealand.
"We had material suppliers, builders and designers all working together for a common goal and it’s amazing when you have the right products, the right people and the right attitude, what can be achieved."
The four properties in the Waiata Shores development comprised a three-bedroom detached house and a three-unit terrace block.
Architype completed the interior detailing for the house and adapted an existing Fletcher Living plan to make the townhouses a low-energy, low-carbon design.
The Dunedin firm specialises in high-performance and passive house buildings, which provide healthy environments while using very little energy.
To ensure global average temperatures stayed within 1.5°C of pre-industrial levels, the
CO2-equivalent generated by a typical New Zealand house during its construction and lifespan needed to be slashed from the current 270 tonnes to 39 tonnes, Ross said.
The detached house in the project came in at 37 tonnes and the townhouses, at 34.
A new home designed to the current Building Code still emits 94 tonnes over a 90-year timeframe.
Fletcher Living head of sustainability Nicola Tagiston said operational carbon would reduce over time as the grid decarbonised and energy efficiency measures came in, making it "really important" to tackle embodied carbon emissions. This was easiest done at the early stages.
"We can really reduce carbon if homes are kept small and simple. Build homes tight and ventilate them right is a must."
There was also "great potential" to find ways to build faster, more accurately and with less waste. The core structure of the LowCO homes — wall panels, floor and roof cassettes — were built off-site, then assembled and made weathertight in one day. Each generated less than a wheelie bin of offcuts.
While considerable planning went into reducing embodied carbon, the designers knew the biggest gains would come from minimising operational carbon.
With this in mind, they set about ensuring the properties would be well-insulated, with an airtight thermal envelope.
Windows are often a weak point in buildings as they literally puncture that thermal envelope. By aligning the thermal breaks in the windows with the thermal insulation in the walls, the architects avoided cold spots on the inside of the window frames. Double glazing was used as Auckland’s climate did not justify triple glazing.
Assessed as Homestar 10 — the New Zealand Green Building Council’s highest built rating — the houses are expected to deliver healthier, more comfortable living with reduced expenses.
Indoor temperatures will be 20-21°C year-round, with heating, cooling and fresh air from a mechanical ventilation heat recovery and exchange system.
Builders wrapped the exterior of the homes in a wood fibre insulation board before adding the cladding, made from Australian hardwood offcuts.
They also installed solar panels on the roof and hot water heat pumps, which use about a third of the electricity of a traditional cylinder.
The suspended timber floor used in the standalone house — and many of New Zealand’s original villas — cost no more than an insulated concrete slab, Ross said. It also meant buildings could be moved if it became necessary because of climate change.
Where the use of concrete was unavoidable — such as the garage slab — it was made from low-carbon cement from Fletcher’s waste tyre-fuelled plant in Northland.
While the properties are connected to water mains, rainwater is also collected and stored in tanks under the floor.
The homes feature water-efficient appliances and fittings.
The kitchen cabinetry is ply and the floors are engineered timber.
The landscaping consists of drought-resistant, biodiversity-rich plantings, including a meadow instead of a lawn in the front yard.
The board used as a garage lining was made from shredded, compressed packaging, each panel containing 25kg of plastics which would otherwise have gone to landfill.
The LowCO project also delivered on that front, with 90% of waste materials being diverted from landfill during construction.
Smart monitoring will capture three years of data on the homes’ energy and water use and help Fletcher’s decide which components to include in its standard builds.
The Sustainable Business Network said on its website the pilot showed the value of modern construction methods, but also highlighted the need for more New Zealand-sourced sustainable products, new supply chain models and more capability in the building sector. "This will be necessary to shift from one-off bespoke builds to low-emission sustainable homes that can be built easily at an affordable cost."
Tagiston said the homes cost about 25% more than a regular build, but the company hoped to reduce that premium to 5-10% as it rolled out most of the initiatives more widely. The operating savings should quickly recover the increased capital outlay.
"LowCO stands as a testament to what we can achieve when we prioritise the needs of future generations and push the boundaries of what is possible in construction today."
"To accelerate this change, we have publicly released all our project intellectual property. The architectural and landscape plans, along with product lists, are available to any builder or homeowner from our website."
Asked about challenges, she said it was important to reduce pressure on the grid by retrofitting existing houses in the short term.
"We also need to help buyers understand which homes are efficient and healthy, and we would like to see energy ratings made mandatory on all houses that go up for sale, just like they do in the UK."
For his part, Ross looks forward to the day when high-performance homes are not only "economically attractive" but also nothing out of the ordinary.
"The goal is to stop talking about things like ‘passive house’ and for it just to become ‘house’," he said.
"That’s happening in some countries already. If you go to places like Belgium, they sell triple glazing on every street corner and passive house is now their building code. They don’t talk about it any more. It’s no longer a thing. It’s just the level they build to."
