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Green Homes For High Quality Living by Johann Bernhardt

Adding passive solar gains by extending an existing home

The good news about designing or building a sustainable green home is that it is an opportunity to improve quality of life whilst saving money. If it is that beneficial, you might ask, why isn't everybody doing it already? I wondered myself. While there might be a variety of reasons for the slow uptake, I can identify two that stand out.

The first is that many people don't know about the many benefits a green home can bring about, and instead choose to focus on the initial, slightly higher financial outlay (maybe 5% of project costs). While costs are usually a primary concern to most of us, the money spent on green features should not be seen as a cost but rather as an investment that will reap rich returns on various levels over time.

The second reason is related to the first. Since the 1950s we have increased the size of our homes on average from 120 sq.m. to about 230 sq.m. while household occupancy has shrunk. Is it any wonder that complaints about unaffordability in the housing sector are dominating discussions? I would have thought that there is a connection between the size of a house and the cost. There is a widespread perception that we should "make the most" of our building project and that aim is too often focused on quantity (size) rather than quality (green).

Connecting the essence of these two statements leads me to the conclusion that if we're smart we limit the size of our building project (new or renovation) to what we need.

So what are the various benefits we can get from a green home?

Let's start with the design. Over many years the passive solar design concept has been developed as an appropriate design tool for the specific climatic conditions in large parts of the country, especially in the North Island. If done correctly space heating requirements in winter can be reduced by up to 80%, sometimes more. But that's not all. If done expertly the list of benefits is a long one. Passive solar design
- Uses solar energy for space heating
- Evens out the ambient internal temperature
- Keeps the house warm and dry in winter and comfortably cool in summer
- Prevents growth of mould and mildew
- Reduces allergic reactions
- Generates healthy, radiating heat
- Creates light and airy internal spaces
- Reduces the need for heating in winter and
air-conditioning in summer, thus
- Reduces power bills considerably and
- Reduces the home's effect on climate change.

But it has to be done properly. Large windows to attract the sun all day in winter won't do it. There is much more to it, it is essential that your architect/designer knows the ins and outs of passive solar design principles. The positioning of the house on the land, a north-facing orientation, large window openings to the North, medium ones to the East and West and minimum sizes to the South. And then there’s thermally broken low-E(emissions) coated double-glazed windows, provision of thermal mass, insulation above Building Code requirements, appropriate shading, good ventilation and passive heat transfer, all of these factors are part of the equation.

Considering our sub-tropical climate, and the opportunities it offers, we would be unwise to forego this unique opportunity.

Equally, it makes a lot of sense to keep the health of the wider environment in mind when building or renovating. The choice of building materials, energy efficiency, water conservation and minimizing the waste we are sending to landfill will all contribute to a healthier natural environment. Considering these topics means going about building in a more sustainable way.

Building materials

We can choose locally manufactured materials, such as plantation grown timbers, natural and low-voc materials. Look out for 'environmental choice'-approved products as the government-endorsed label provides an independent guide for products that are better for the environment.
Tropical hardwood timbers, often used for decking and outdoor furniture, should be treated with caution as most of them have been logged illegally or unsustainably, unless they display an FSC-certification. Alternative timbers include locally sourced, un-treated plantation-grown macrocarpa, douglas-fir, eucalyptus, cypress species, cedar and redwood or even recycled hardwoods like totara and jarrah.


With the price of photovoltaics (pv) for electricity generation having come down dramatically over the past few years it is now an affordable option to beat the continuously rising power bills by using our roofs for their installation. And since it is estimated that saving energy costs roughly 10% of generation it would be wise to look at all the energy saving options around the house first in order to minimize the size (and costs) of the pv panels.

Some of the most effective ways to save energy are:

- Applying passive solar design for space heating as described above
supplemented by a free-standing log burner with efficiency levels of up to 85% as opposed to an open fireplace (around 15% efficiency)
- Installing a wetback on the log burner for water heating
- Choosing solar water-heating panels or air-conditioned water heating
- Having energy-efficient appliances
- Providing natural light and energy-efficient light bulbs
- Using passive ventilation like open able windows and trickle-vents in window frames.


Water is a vital resource, but it can be a scarce resource. It makes sense to use it wisely to maintain the natural hydrological cycle. We can

- Catch roof water and use it for toilets, washing machines and the garden
- Position the hot water cylinder close to kitchen and bathrooms
- Install flow restrictors in kitchen sink, showers and vanities
- Install dual flush toilet cisterns
- Minimise impermeable surfaces (driveways) and create rain gardens as an additional local storm water management tool.

Waste Minimisation

The construction of a typical family home in New Zealand generates up to 7 tonnes of waste. This is a waste of valuable resources, as well as a strain on the environment. Options to minimise the waste we generate involve reducing the house size and materials used in building, re-using materials, repairing what can be reused and recycling what can't be reused or repaired. The result is a reduced amount of waste to be responsibly disposed of.

Discussing waste minimisation equates to an increasingly popular construction method, which is pre-fabricated modular and transportable houses. The standardisation of these houses and their economical production makes the minimisation of waste relatively easy and achievable. Assembled in factory spaces, free of weather conditions, speeds up the construction time and costs. There is a range of options on the market, including some great sustainable designs with many of the green features mentioned above.

In a nutshell, these are the benefits we get from building a green home:

- Passive solar design gives us free heating in winter and creates healthy indoor environments
- Energy efficiency measures reduce the amount of energy we use and the costs for electricity year after year
- By installing photovoltaic panels we can achieve total independence from electricity providers and their continuous price increases
- The use of natural and low-voc building materials, good insulation, double-glazing and natural ventilation will all help to create warm, dry, comfortable and healthy indoor spaces all year round
- Catching water from the roof and using it for garden and toilets reduces reticulated water use and its cost. It also contributes to a better local water management, especially if we use it for food production (more savings and healthier)
- Minimising waste benefits all of us and in particular the environment.

Johann Bernhardt has been designing green, sustainable homes for many years. He has published the book 'A deeper shade of Green' – the only comprehensive book on sustainable urban development, building and architecture in NZ. Currently Johann teaches at the architecture school of the University of Auckland.

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