What makes a green home?

You don’t need millions of dollars, an architecture degree or the urge to build a mud hut to live in an eco-conscious building. It’s easy to have a healthier, more comfortable home with lower bills and less environmental impact by applying some simple principles when buying, renovating and redecorating. Here are the eight basic things that help make a home kinder to the environment – and often better to live in.

1. What the home is made of – embodied energy

The first thing to consider is if we need a new house at all, or whether it might be more efficient in terms of the ‘embodied energy cost’ to renovate an older building or reuse old materials. Thinking about embodied energy is an attempt to take into account all the energy, materials and natural resources used for something. For example, a log cabin in the woods might require some trees, some basic hand tools, and the food, clothing and shelter our modern-day Grizzly Adams will use making it. A concrete and steel building might need all the ingredients for the concrete, the mining of the metal ores, their transport to the production site, the machines that processed them, trucks to get it all to the site, and more.

Calculating this can be complex, but even a rough assessment can remind us how choosing more local, recycled or natural materials like earth, straw and wood may reduce the environmental impact of our home. Could we make shelves from firewood off-cuts instead of driving out to the store to buy something from China?

Generally the smaller and simpler the home, the less energy is used to build it, and the less impact its construction has on the local environment. Not to mention, the more you are likely to have left in the budget for higher quality eco-conscious materials.

2. How the house is positioned

Passive solar is about making the most of the sun. The most impressive results can be achieved by installing large windows on the northern side of the building, over a substantial bare stone, tiled or rammed earth floor. This floor is referred to as a thermal mass – it traps the warmth for later and slowly releases it back into the room. Insulated block walls also have a similar effect. Eaves over the windows prevent overheating in summer sun, but let as much of the low winter sun in as possible. Windows, doors and the layout of internal walls can all be similarly adjusted to maximise solar gain.

For example, a bedroom on the north-eastern side of the house may allow you to wake up with the sun, while a dining room to the north-west may make the best of the sunset. An open-plan living area may be favoured over a more private layout behind an internal wall, which might otherwise need additional heating. Homes that use passive solar design and thermal mass to best effect often need little or no heating at all.

3. Heating

The World Health Organization recommends a minimum indoor temperature of 18°C for all rooms, with the living room at a minimum 21°C, to avoid an increased risk of respiratory illness.

The extraction of fossil fuels like coal, gas, oil and diesel for heating, damages the environment, as does the burning of those fuels around the world, not least because of the greenhouse gases this releases. Thankfully, more than three quarters of New Zealand’s electricity supply is generated from renewable sources, including geothermal stations, hydropower and wind turbines, and we have an electricity grid that covers most locations. Heat pumps are the most efficient way of turning this electricity into heat. They are quite an investment at anything between $1,300 to $3,000-plus, but the best of them produce the equivalent of $5 worth of heat for every $1 spent on the power. (Get more information on heat pumps here.)

The impact that wood burners have on the environment largely depends on where the firewood comes from, how well it is dried, and how efficiently it is burnt. Modern burners, costing $3,000 upwards to buy and install are highly efficient and produce few emissions.

The latest pellet burners cost a little more. They use recycled sawdust pellets for fuel that might otherwise be simply disposed of as waste.

Meanwhile, solar panels are the eco-choice for generating hot water, as long as you have a sunny enough spot for them. However, these systems cost between $4,000 and $8,000.

4. Windows

Recent changes in New Zealand’s building regulations have improved standards generally and particularly increased the use of double-glazing. The UK’s independent Building Research Establishment has assessed timber, aluminium and steel window frames using 13 different environmental criteria, ranging from human health and climate change to waste disposal and ozone layer depletion. Painted hardwood-framed double-glazed windows did best, alongside the best preservative-treated softwood framed windows.

In New Zealand there are increasing numbers of experienced companies offering frames in native woods, imported timber and uPVC plastic options, as well as aluminium frames that are the least expensive but can transfer hard-won heat to the outside world via their metal frames. This problem can be overcome by choosing thermally broken frames, which cost more but include insulation to stop this happening.

5. Keeping things snug – insulation

Insulation traps a blanket of air around your home to maintain a comfortable temperature inside. The R-value of insulation materials tells you how good they are at holding the heat. A thin layer of glass fibre insulation may have an R-value of something like R2, whereas a single layer of polyester ‘fleece’ may have only half that. Most insulating materials come in varying weights and thicknesses, and can be combined to create the desired effect.

The government has set legal minimum R-ratings for insulating new homes, additions and alterations. For the colder South Island and Central Plateau roofs require R3.3 insulation, walls R2 and floors R1.3. Everywhere else in the country roofs need R2.9, walls R1.9 and floors R1.3. Beyond that, what you need depends on local weather and your personal preference, but the better the insulation you invest in, the less you are likely to have to spend on heating. The Passiv Haus approach, for example, which was developed in Germany, uses insulation up to R50 to create homes that require no heating, even in the depths of winter.

Leading insulation companies now provide comprehensive information on the health and environmental impacts of their materials’ production, installation and use. New Zealand-produced options include recycled glass products such as Pink Batts (www.pinkbatts.co.nz), recycled polyester products such as Greenstuf (www.autexindustries.com) and recycled wool such as Ecofleece (www.ecoinsulation.co.nz). Prices range from $6.50 a square metre for R2 to more than $20 a square metre for up to R6. Good installation is vital to getting a good result; go to www.energywise.govt.nz to find out more.

6. Seeing the wood for the trees

To avoid contributing to deforestation problems, it’s important to choose timber certified as sustainable by the Forest Stewardship Council (www.fsc.org) or the Rainforest Alliance (www.rainforest-alliance.org). It’s also worth checking Greenpeace’s Good Wood Guide (www.greenpeace.org) to find out more, especially when buying imported wood.

How the wood is treated is another factor. New Zealand-grown pine is easy to get and relatively inexpensive. However, to make it last against the elements, fungus and insects it is commonly treated with Light Organic Solvent Preservative (LOSP), which is based on white spirit, or Copper Chromium Arsenic (CCA). These days the process has fairly strict health and environmental controls, but treated timber still becomes hazardous waste at the end of its useable life and must be land-filled. On the other hand it’s possible to buy timbers such as macrocarpa heartwood that are sustainably harvested and don’t need treating due to their natural properties, though this can be costly.

7. Paint

Volatile Organic Compounds (VOCs) including benzene, formaldehyde, toluene, and xylene are used as solvents in some modern paints and in most paint strippers. According to the Twelfth Report on Carcinogens published by the US National Toxicology Program, benzene and formaldehyde are known to cause cancer in humans. Increasing awareness of this, and previous issues with older paint additives like lead, has inspired a wide range of ‘natural’ low VOC or VOC-free paints. This reduces indoor air pollution and means brushes, rollers etc can be cleaned with ordinary soap and water. Some companies even offer paints made from plant oils, tree resins and earth clays. Big names like Resene, Dulux and Wattyl/Taubmans all have low-VOC options, or you could try the fully natural approach of companies like Biopaints (www.biopaints.co.nz).

8. Water

The environmentally conscious use of water is about where your water comes from, how long you can keep it cycling through your home for different uses, what ends up in it while it is there, how it gets cleaned up again and where the water and waste go next.

Installing low-flow taps and shower heads can reduce water use, as well as the latest efficient washing machines, dishwashers, and your own habits. However, if building or renovating you might consider options like a rainwater tank filled from the roof. This can then be filtered for drinking as well as bathing, dishwashing and clothes washing. If you only use cleaning products made from benign natural ingredients the run off from the sinks can then be diverted and collected as ‘grey water’ by systems like ECOplus (www.wastewater-recycling.co.nz), at a cost of $3,500 plus installation, to irrigate the garden. You could use this to flush standard toilets too, or install composting toilets that ‘flush’ with wood waste or sawdust to break down the waste for safe use fertilising the garden.

Have you built an eco home, or made green renovations? We’d love to hear about it. Email [email protected] or post a comment below.