What are greenhouse gases?
Greenhouse gases are gases in the atmosphere that trap heat. They let sunlight reach the Earth but stop the heat that the sunlight brings from leaving the atmosphere. They act just like a greenhouse, affecting our climate. Greenhouse gases include carbon dioxide (CO₂), methane, nitrous oxide, ozone and chlorofluorocarbons.
Greenhouse gases don’t all cause equal harm. Some have much higher global warming potential (GWP) than others. The GWP of a gas indicates the contribution to global warming resulting from the emission of one unit of that gas compared to one unit of carbon dioxide, which has a value of 1.
For example, R-134a (tetrafluoroethane – a traditional refrigerant used in some heat pumps) has a GWP of 1300.
What is embodied carbon?
Embodied carbon is the amount of greenhouse gases required to produce a material, expressed as a carbon dioxide equivalent. It is basically that material’s carbon footprint.
Embodied carbon can be assessed over different periods, such as:
- cradle-to-gate, which covers resource extraction through to factory gate (before it is transported to site)
- cradle to site, which includes all a material’s emissions up to the point it reaches a building site
- cradle to grave, which is a whole-of-life approach from manufacture and installation to demolition/disposal.
What is net-zero carbon?
Net-zero carbon is when human-caused emissions are reduced to as close to zero as possible. Any remaining greenhouse gas emissions produced would be offset with an equivalent amount of carbon removed from the atmosphere – for example, by planting forests.
What is biogenic carbon?
Biogenic carbon involves biological sources such as trees, plants and soil. In a carbon cycle, trees capture CO₂ from the atmosphere during photosynthesis and store it. The carbon that has been sequestered in this way is released at a later stage when timber is burned or rots away. Because timber stores carbon, assuming it comes from sustainable forests (replanted after harvest), it has a low carbon footprint as a house material.
What is a carbon footprint?
A carbon footprint is the amount of greenhouse gases – typically measured as carbon dioxide equivalent – released into the atmosphere by a particular human activity or good or service. A house has a carbon footprint, which is the sum of all greenhouse gas emissions produced as a result of its construction, occupation and demolition.
How is a carbon footprint calculated?
A carbon footprint is calculated by identifying and measuring all the greenhouse gases emitted as a result of an activity. For example, a building’s carbon footprint would include the emissions that came from the manufacture of the building materials and the transport of materials to the site, the energy and water used in the building itself and so on. There are standards and guidelines for making these calculations. You can find more information in the BRANZ bulletin BU679 Introduction to calculating whole-of-life carbon footprints of houses.
What is a carbon budget?
A carbon budget for a New Zealand house estimates the volume of emissions that a new house can be responsible for while still moving towards New Zealand’s 2050 net-zero carbon goal. Calculations show that, in carbon terms, typical new builds today are over budget – they have larger carbon footprints than they should have. You can find more information here.
WIDER CLIMATE CHANGE ISSUES
If climate change will lift temperatures by just 1.5°C or 2°C, that doesn’t seem like a problem – why are we bothering?
Temperature changes are not evenly spread around the country and around the world. Due to climate change, an average 2°C global warming will see more extreme heat waves in some locations. For example, in 2015, India and Pakistan saw deadly heat waves when temperatures remained continually high and hit 49°C. The extreme heat resulted in thousands of deaths. An increase in global warming of 2°C would likely see extreme heat waves become an annual event.
Even minor average temperature changes have a huge impact on drought. It has been estimated that, if the average global temperature increase reaches 2°C rather than 1.5°C, about 61 million more people in the Earth’s urban areas would be exposed to severe drought.
In New Zealand, just small average increases in temperature could result in more heat waves, droughts and water shortages in already vulnerable areas.
Is there any evidence of climate change happening in New Zealand right now?
There is considerable evidence that our climate is changing:
- Our temperatures are getting warmer. Seven of the past nine years have been among the warmest on record. The winter of 2022 was the warmest and wettest ever recorded.
- Sea levels around New Zealand have risen by up to 220 mm in the last century and the speed of sea level rise has increased.
- The South Island’s glaciers have lost 25% of their ice in the past 4 decades.
- Many locations are seeing drier soils and changing rainfall patterns. Auckland had a record-breaking drought in 2020.
There’s been talk of more flooding, more droughts, higher temperatures, higher sea levels and so on – which are going to affect us most in New Zealand?
All of these issues are going to affect us, with many already having an impact.
In mid-2020, the government released the first National Climate Change Risk Assessment for New Zealand. It found that the biggest issues facing the built environment are risk to potable water supplies and risks from extreme weather events and sea-level rise.
The risk to water supplies (availability and quality) due to changes in rainfall, temperature, drought, extreme weather events and sea-level rise was rated most urgent of the 10 most significant risks that require action in the next 6 years.
Other research indicates that, by 2050, the number of hot days (>25°C) in many locations could double from the figures today. Auckland and Christchurch could see an extra month of hot weather each year.
REGULATIONS AND INTERNATIONAL AGREEMENTS
What is New Zealand legally committed to doing around climate change?
New Zealand’s biggest commitment is to reduce net emissions of greenhouse gases (except methane from plants and animals) to zero by 2050. This is set out in the Climate Change Response (Zero Carbon) Amendment Act 2019.
New Zealand is a signatory to the Paris Agreement – a United Nations initiative where countries commit to take action to reduce the threat of climate change. Under this agreement, New Zealand committed to keeping its 2030 net emissions (gross emissions less carbon sequestration from forestry) at least 50% below its 2005 gross emissions by 2030. (This was updated in 2021 from our original commitment of 30%.)
If the law doesn’t require us to be net-zero carbon until 2050, why are we acting now?
BRANZ calculations show that New Zealand’s current house construction methods and materials produce too many emissions to help meet climate targets. It is going to take time to educate the industry and the public about what is required. Some upskilling of industry practitioners will be required, as will changes in the choice and use of building materials. It is a big project and will take many years to achieve.
Right now, there is no law requiring houses to produce fewer emissions – will that change?
Yes, over coming years laws and regulations will be brought in that require changes in the way we build. In mid-2020, the government announced the Building for climate change programme as part of this process.
The government has said that: “To meet the goals, we’ll need to make some changes to current building laws – both the Building Act and the Building Code … At first, we’ll be focusing on how we can build new buildings better. In the future, we’ll also likely need to look at what changes need to be made to existing buildings.”
NEW ZEALAND BUILDING INDUSTRY
Aren’t farm animals the real greenhouse gas problem in New Zealand? Why does the building industry need to change?
If we consider all the energy our buildings use and a building’s full life cycle – manufacture of materials, building construction and demolition – the built environment accounts for approximately 16–20% of New Zealand’s greenhouse gas emissions. While it is true that a large part of New Zealand’s greenhouse gas emissions come from animal sources (and from transport), the built environment still makes a significant contribution as its impact is across several sectors.
Where are greenhouse gases emitted in New Zealand house construction and operation?
A large part of the greenhouse gas emissions from a new house over its whole service life come from the energy used for plug loads, water heating, space heating and so on. Building materials also account for a significant proportion and water use for just under a tenth of total emissions.
Of the building materials we commonly use in New Zealand houses, which are responsible for the most greenhouse gas emissions and which the least?
Steel and concrete have the largest carbon footprints. When steel roofing and concrete floor slabs are used in a house design, they are typically the highest contributors, by material type, of carbon. Both the steel and concrete industries are researching ways to reduce the carbon footprints of their products.
Bio-based materials such as timber and engineered wood have advantages in net-zero carbon construction because they have captured and stored atmospheric carbon dioxide as the timber was growing. It is crucial that these products are grown sustainably, with forests replanted after timber is harvested. New Zealand forestry is generally considered sustainable. Sustainably grown timber may have a certificate provided by the FSC (Forest Stewardship Council) or PEFC (Programme for the Endorsement of Forest Certification).
Will the shift to building net-zero carbon houses be a big move for the Kiwi building industry, or does it just require a few small changes?
Some houses being designed and built today already have much lower carbon footprints than others. We already have a lot of the information we need to be able to design and build net-zero carbon houses (although realistically, none are actually being built). In some aspects – like making our houses better insulated and appliances far more energy efficient – we are making progress.
The challenge is that all practitioners need to be brought up to speed, and all new houses will need to be designed and built to meet the 2050 goal. In large part, we know what we have to do – it is the scale and the logistics of the change that is the hard part.
What does a net-zero carbon house look like?
At first glance, a net-zero carbon house doesn’t look radically different from the new houses being built today. It may be slightly smaller than many recent new homes, and there may be greater use of certain types of material, such as timber. South-facing windows may be smaller than on some homes. There will be eaves or shading devices, especially on the north-facing side, to reduce summer overheating.
Many of the changes are not visible or obvious – for example, the much higher levels of thermal insulation in the walls and ceiling, the higher-performing windows and glazing and the heat pump water heater with CO₂ as a refrigerant.
ARCHITECTS AND DESIGNERS
What reliable, New Zealand-based tools and resources can I use in designing net-zero carbon houses?
BRANZ has already developed several tools to help:
- LCAQuick is a free tool that evaluates the carbon footprint and other environmental impacts of a building design.
- CO₂NSTRUCT provides values for embodied greenhouse gas and energy for some construction materials.
- You can find other resources and guidance on the BRANZ website.
My clients are extremely cost-conscious. How can I persuade them that they might need to spend a few dollars more on their new home to reduce emissions?
It is very common for New Zealanders to think a great deal about the upfront cost of a new house (or significant renovations) and very little about the running costs. Part of the approach to costs should be an explanation that things such as higher levels of insulation and glazing will make their house much warmer and more comfortable to live in and reduce the costs of space heating to keep a house the same temperature.
Clients should also understand that it is almost always cheaper to install features such as a higher level of wall insulation at the construction stage than as part of a retrofit a few years later.
My new-home clients all focus on what they can see – granite benchtops and fancy tapware. How do I talk to them about climate change?
Stories about climate change are regularly a part of mainstream news media, so most clients will already know something about it. It is up to designers and builders to explain:
- how new homes need to be able to cope with the impacts of climate change, such as higher temperatures, more frequent extreme weather events and so on
- how new homes must produce fewer greenhouse gas emissions.
A practical approach may be best – explaining how some water heating systems and space heating systems produce far fewer emissions than others, for example. Flag to your clients that, when they are selecting any part of the house, from the wall cladding to the showerhead, this should be part of their consideration.
I am not an expert on climate change so why should I take any responsibility in this?
The simple fact is that all of us are affected by climate change and all of us need to be involved in dealing with it. As with other challenges such as COVID-19, we need to see ourselves as a team of 5 million and work together.
Over coming years, there will be regulatory changes that everyone will need to abide by, but life will be easier if we make changes as we can rather than waiting to have them imposed on us.
My client base prefers larger houses – well over 200 m². Is it just as easy to design a large net-zero carbon house as a smaller one?
In general terms, the bigger the house, the bigger the carbon footprint. This can be true even for high-specification houses with better insulation and glazing. The energy efficiency in their design may mean less energy is used for space heating, but their size alone requires more materials to build and maintain, and this means more greenhouse gas emissions. Designing a large net-zero carbon house is possible, but it is more difficult than with a smaller house.
If I want to bring net-zero carbon ideas into my work, where should I start?
A good approach would be to introduce the idea with clients very early in the design process. Help them understand the basic concepts and guide them to include a consideration of greenhouse gas emissions in their decisions. There is a huge overlap between areas such as good passive design and energy efficiency – concepts already well known in the industry – and net-zero carbon construction.
In the broadest terms, there are two key areas designers can address: the orientation and layout of the building and the thermal envelope – the specification of cladding, windows and glazing, insulation and so on.
My wealthy clients want a house design that I know has a huge carbon footprint. Is it OK to go ahead if they pay to have trees planted somewhere to offset the carbon?
It is true that offsetting is a consideration in net-zero carbon planning, where greenhouse gas emissions produced are balanced with an equivalent amount of carbon removed from the atmosphere by planting forests. This is not seen as an equitable or acceptable long-term approach. As construction laws and regulations are introduced or amended to require new building work to be net-zero carbon, exemptions such as this for new homes with large carbon footprints are unlikely to be included.
BUILDERS AND TRADES
The big decisions around house design and materials are all made by clients and designers – why should builders think about this?
Builders have a key role to play in constructing net-zero carbon houses. Consider just two areas – materials installation and waste:
- The quality of construction and installation of building materials and elements can have a big impact on all areas of a house, from weathertightness to energy efficiency. Thermal insulation is a classic example if it is poorly installed or temporarily removed and not properly restored by subsequent trades.
- On-site practices can have a significant impact on the amount of building waste that goes to landfill (and the more waste, the higher the levels of emissions). There are many ways of reducing waste, from ordering the right quantities at the right time, storing materials on site so they are not damaged, reusing offcuts where possible and so on.
If I build a net-zero carbon house, what will I be doing differently to what I do today?
Most of the building techniques in today’s houses are also used in net-zero carbon houses. It is the materials, building elements, fixtures and appliances that are more likely to change. Key differences are likely to be:
- an increased use of certain materials and reduced use of others because of the emissions produced during their manufacture
- significantly higher levels of thermal insulation
- higher-specification windows and glazing
- certain types of appliance used much more frequently (such as heat pump water heating rather than the common electric storage water heaters or gas instantaneous heaters).
I never learned anything about this during my apprenticeship 20 years ago - where do I find information?
There is already information available on the BRANZ website and in many issues of Build magazine. Local authorities are producing information – ask your local Eco-Design Advisor if your council has one. The New Zealand Green Building Council also has useful information.
NEW HOUSES/HOMEOWNERS
We are about to start looking for a section to build our dream home on – do we need to think about climate change?
Choosing a building site is the best time to think about climate change and net-zero carbon building. Some councils (not all) place information on a land information memorandum (LIM). The choice of a site can have a huge impact on the carbon footprint of a house and its future energy use and running costs.
Choose a site with as much all-day sun as you can get and a size/shape that lets the living spaces of your home face north, and your home can be designed so it is kept warm mostly by the sun (and has lower energy bills). A house on a site that sees little sun will typically require higher amounts of purchased energy, have a bigger carbon footprint and come with higher running costs. Rectangular sites that run east-west are generally preferable to sites running north-south.
The ideal site will also be within walking/cycling distance of shops and other services or at least on a bus or train route so you do not need to use a car every time you go out.
Is a net-zero carbon house going to cost us a whole heap more dollars than a standard new home?
First, it is important to bear in mind the two types of cost that come with home ownership – building or buying a home and running a home. Very often, people focus just on the upfront cost of getting into a house but forget the thousands of dollars a year spent in running costs. As net-zero carbon houses are very energy and water efficient, that means that their running costs (buying electricity or water) are likely to be lower. This should be borne in mind when the upfront costs are considered.
Second, remember that house size is also a crucial consideration. Bigger houses, including bigger net-zero carbon houses, are more expensive to build. You may find that, if you focus on good design rather than size, you can get a house you are very happy to live in for little if any more than an older style of house that does not consider carbon or climate change.
EXISTING HOUSES/HOMEOWNERS
What does climate change have to do with my old house?
The move to a net-zero carbon economy by 2050 doesn’t just affect the new homes we are building. A large part of our building stock today will still be around in 30 years’ time and will need to contribute to the target – for example, by being much more energy efficient.
The government has hinted that we will need to upgrade our housing stock in coming years. A good approach would be to take any opportunities you see for upgrading your home. There are already grants and interest-free loans available from government programmes, some local councils and some banks for making energy efficiency improvements to existing houses.
What can I do to my house to help reduce carbon emissions?
There are many things homeowners can do to reduce the carbon emissions from their home. Some (such as adding insulation to uninsulated walls) are likely to be best done as part of a major renovation, but other steps can be taken at any time:
- Add insulation. Insulate an uninsulated roof space or add insulation to one that is poorly insulated. Fix insulation under uninsulated suspended floors.
- When replacing an old space heating system, choose a heat pump or a log burner/pellet burner and burn wood from sustainably grown forests (or waste wood).
- When replacing an old water heating system, opt for a heat pump water heater (preferably with CO₂ refrigerant) or an electric-boost solar heater system designed and installed by experts.
- Reduce water use. When replacing a clothes washing machine, choose one with a WELS rating of 4 stars or above. Replace a showerhead that uses a lot of water with one that uses 9 litres per minute or less. Fit aerators/flow restrictors to bathroom taps. Design a garden and garden irrigation so you don’t need to use sprinklers.
Updated: 16 October 2023