Windows: In the frame

Glazing of both windows and doors is what allows the outside environment to interact with the interior of the house, a relationship that can be both good and bad. It’s good when we open doors and windows up to allow cool summer breezes inside, but it’s bad when all that glass sucks the warmth out of a room on a frosty winter evening, or lets the hot afternoon sun heat up the internal temperature to unbearable levels.

Glazing is usually the Achilles heel of a building’s performance and should be one of the very first things to go under the microscope when considering a building upgrade. An otherwise well-insulated house can suffer considerable unwanted heat loss or heat gain through single-pane glass, which has almost no insulating ability – around R0.15.

The Australian Window Association (AWA) estimates that up to 40 per cent of a home’s heating energy can be lost through windows and up to 87 per cent of its heat gained through them. Choosing high-performing windows and placing them appropriately can reduce energy costs significantly and improve thermal comfort. The art is in knowing how different windows will interact with the design of your home.

But where do you start to work out which glazing system or treatment is the best solution for you? It’s a complex task even for a switched-on homeowner. The AWA has made things easier with the Window Energy Rating Scheme (WERS).

Window performance measures

WERS simplifies window comparison by rating the performance of residential windows using a star rating system, much like star ratings for appliances. The star ratings are based on the window’s basic performance measures: U-value and solar heat gain coefficient (SHGC). Windows receive a rating for both heating and cooling performance. WERS has three climate types for the whole of Australia (and New Zealand fits one of these): heating, cooling and mixed. The zones indicate whether most energy will be dedicated to heating or cooling to maintain thermal comfort, and mixed means just that – about equal shares of both.

The whole-window U-value (Uw) measures how readily a window conducts heat. The lower the U-value, the greater a window’s resistance to conductive heat flow and the better its insulating value. WERS gives comparative ratings for frames and glass combined in a functioning window or door. If we use old-school aluminium frames plus single glazing as a benchmark, modern aluminium frames, thermally broken frames and some uPVC frames plus double glazing (insulated glazing units or IGUs) can reduce internal to external thermal transfer (conductivity) by 50 to 75 per cent or even more. Timber frames (softwood) are about equivalent to thermally broken aluminium frames; steel frames are not proven high performers. More on frames later.

The other important factor influencing window performance is its whole-window solar heat gain coefficient (SHGCw). This measures the window’s ability to control heat transfer from solar radiation. This coefficient is expressed as a number between 0 and 1 – the lower the number, the less solar heat the window transmits.

Real-world U-values normally fall between about 8 (worst case) down to 1 (best case). Real-world SHGCs range from about 0.75 down to 0.15. Unlike U-value, we don’t tend to label high SHGC as ‘bad’ and low SHGC as ‘good’ as the judgement depends on the climate where the building is located. In almost all cases, a low window U-value is better in all climates.

Single, double and triple glazing

In general, all windows will benefit from having better insulating properties – that is, from double or triple glazing or from insulating window coverings. These technologies slow down the conductive heat flows in both directions.

Double-glazed windows are far superior to single-glazed windows for insulating your home. If you’re wondering whether the added cost of improved glazing is worthwhile, consider that compared to single glazing, in cold and mixed climates a double-glazed window could cut your window heat loss by 60 per cent or more, reducing heating loads.

Some people may simply choose to replace leaky old windows with double glazing, with good outcomes. But for anyone currently in the process of assessing quotes and specifying energy-efficient windows, you will already know there’s a lot more to consider than multi-pane glazing to achieve optimal results.

Tilt-and-turn windows can be opened wide with the hinge to the side, or – by turning the handle in the other direction – tilted open a little at the top for ventilation. Paarhammer’s tilt-and-turn windows feature German metal hardware with multi-point locking and a layer of compression seals. When the window is closed, the locks all around the window press the sash into the frame and the seal engages, eliminating draughts. They can be fitted with either double or triple glazing. Image courtesy Paarhammer.

Tilt-and-turn windows can be opened wide with the hinge to the side, or – by turning the handle in the other direction – tilted open a little at the top for ventilation. Paarhammer’s tilt-and-turn windows feature German metal hardware with multi-point locking and a layer of compression seals. When the window is closed, the locks all around the window press the sash into the frame and the seal engages, eliminating draughts. They can be fitted with either double or triple glazing. Image courtesy Paarhammer.

Glass coatings and tints

Coated and tinted glass can be used to improve the performance of single-pane windows or to turbocharge the performance of double- or triple-glazed units to make them even better.

Tints use a pigment in the glass to reduce solar heat gain and light transmission; coatings are applied to the surface at the factory and can be reflective (‘mirror’ glass) through to higher-end low-emissivity (low-e) coatings.

Low-e coatings reduce the onward transfer of radiant heat, and so can reduce heat loss or gain through the glass. The coating can be tuned to reflect most, some or very little of the radiant solar heat, depending on the needs of the climate and orientation. This approach can reduce the SHGC by more than 60 per cent compared with clear glass and is often used in warmer climates or for west-facing windows when trying to minimise heat from the sun, while still retaining daylight.

From a solar heat gain point of view, the location of a low-e coating is quite important. In hot climates or for unshaded windows facing east or west, a low-e coating should be on the inside-facing surface of the outer glass layer and should be a coating with low solar transmittance (thus, low SHGC). In climates with cold winters (most of southern Australia) where passive solar gain is needed, the coating should be on the outward-facing surface of the inner glass layer for optimal results. Getting it the wrong way around will reduce performance by about seven per cent. It may not sound like much, but to get a seven per cent boost at no extra cost simply by careful specification and correct assembly is definitely worth it!

When dealing with suppliers it is helpful to have a basic understanding of the technical aspects and what their implications are. It is possible to inadvertently select glazing for an energy-efficient building which blocks all heat flow. Sadly, we know of one instance where the passive solar design has been largely nullified by heat-blocking glass purchased on the basis of it being the ‘smart’ option. It was the wrong specification, because the building’s shading design kept the summer sun under control, but now the winter sun’s warmth is kept out too. On sunny days, the owners have to open the north-facing sliding doors to allow the sun to pump some heat directly into the slab floor – a less than ideal workaround.

Shading and glazing selection

Selection of the type of glass and coatings for your windows can be a daunting process. There are some general guidelines that apply, depending on your climate zone and the window orientation, but many factors come into play, including the design of your home and the size of the windows. Careful tuning of windows based on orientation can help maximise the result, combined with the use of good summer-only external shading and internal curtains or blinds with pelmets.

The trick is to tune how you control the flows of radiant heat. For example, in warmer climates or for westerly windows, you’ll generally want a low solar heat gain, thus always reducing the amount of heat getting in. In cooler climates on northerly windows, you’ll generally want a high solar heat gain, to allow the winter sun into the interior, but you may also want to reduce radiant heat transfer back through the window with a low-e coating (described above). For all window orientations, you need to take into account the window size and external shading. This is best done in conjunction with a professional designer or thermal performance assessor.

Correct shading is particularly important with double glazing. This is because incoming solar radiation is in short wavelengths, which passes through glass rather easily, heating up everything it strikes. These warm surfaces then re-radiate heat but in long wavelengths, which do not pass through glass as easily, and thus we get a net build-up of heat – which is why cars get so hot when parked in the sun. Double glazing exacerbates this accumulation of heat. Passive solar design uses this to provide free heating, and passive cooling excludes the solar radiation (by shading) to prevent it from getting inside in the first place.

Frames, ventilation and thermal break

Frames are an important part of the heat transfer equation, and while it is entirely possible to have energy-efficient glazing in any style at all, the performance of a frame needs to be considered in conjunction with the glass type.

The most popular type of frame is the all-aluminium frame, but aluminium is a great conductor of heat and so provides no insulation. However, aluminium frames can be made to perform better by introducing a ‘thermal break’ in the centreline of the frame. This consists of a structural insulator between the inner and outer frames that is made from timber or plastic (usually a polyamide such as nylon).

A number of manufacturers now make ‘composite aluminium’ frames – aluminium on the outside and timber on the inside, which can look attractive and effectively creates a thermal break.

When selecting a frame design it's important to consider air movement including where the desirable and undesirable breezes come from, and the best arrangement for any operable window sections to take advantage of them; bearing in mind all window designs need to account for falls. All of these factors have been executed beautifully in this POD-designed house in Cairns.  Image: Nic Granleese

When selecting a frame design it’s important to consider air movement including where the desirable and undesirable breezes come from, and the best arrangement for any operable window sections to take advantage of them; bearing in mind all window designs need to account for falls. All of these factors have been executed beautifully in this POD-designed house in Cairns. Image: Nic Granleese

You might prefer other framing materials; these include all-timber (making sure it is sustainably sourced), uPVC plastic (unplasticised polyvinyl chloride), and even fibre-reinforced plastic (fibreglass). Steel framing is making a comeback, but the old-style profiles were not good thermally, whereas some new profiles take conductance and sealing seriously – but always check the WERS rating.

When selecting a frame design it’s very important to consider air movement: where do the desirable and undesirable breezes come from? What is the best arrangement of any operable sections of the window to take advantage of these? Safety and falls prevention considerations in the building codes now require a window to be designed to prevent children from falling out. Sounds reasonable, but it is often poorly implemented, by means of limiters that prevent the window from opening more than 100mm, which will not allow proper ventilation.

Careful use of louvre windows may be a good option to consider. The usual question then thrown up is about them being single glazed – but in most temperate climate zones, a mix of, say, 25 per cent of louvres combined with 75 per cent fixed IGUs provides sufficient overall insulation capacity, combined with excellent controllable secure ventilation. But make sure they are designed to fully seal when closed. Once again, good thermal modelling using simulation software can guide these design details.

Weather seals

A window allowing air movement through it even when closed will be a poor insulator, no matter what its materials and construction. Windows that have moving sections should have good seals between the moving sash and the fixed frame. Most modern commercially made windows have a reasonable seal, but their effectiveness depends on how well the window is designed and manufactured. The amount of air that passes through an area of window under a given pressure is known as the infiltration rating – the lower the value, the better.

Compression seals (as seen on awning, casement and tilt-and-turn windows) usually seal better and last longer than brush seals commonly fitted to sliding or double-hung windows.
A good seal between the window frame and the wall is also very important. It is not uncommon to see windows with gaps and considerable air leakage between the frame and the wall – this means that energy saved with improved glazing can be lost through the frame.

Double glazing retrofit and window film

Other than entirely new windows, there are other ways to achieve better window performance. There are several aftermarket double-glazing products, such as Thermawood which replaces the glass with a double-glazed unit, or Magnetite which is designed to improve but not replace existing single-glazed windows. This may be a consideration, especially to avoid waste if your existing frames are in good condition.

Another way to improve the performance of your existing windows is through the application of film. Film can be considered to be a lot like a factory-fitted coating on the glass, but instead it comes on a roll and should be fitted by a professional. Films come in many types, including spectrally selective and low-e, and vary in performance and what they actually do – the trick is to select a film that does what you need it to do, depending on the local climate, the orientation and location of the window, and the performance of the rest of the house.

Even more improvements – insulate!

Renovations should always make the house better, and this should include all the windows if at all possible. But many existing houses may have other problems that cause them to be too cold or hot (usually too cold in southern Australia and New Zealand). Apart from the obvious likely culprit of poor or missing ceiling insulation, other miscreant elements include uninsulated subfloors, leaky and ill-closing windows and doors, gaps in floorboards and under skirtings, wall vents (no longer required), absent pelmets – the list goes on. Most of these problems are easily solved and should be tackled with pocket money before any serious money is spent on new windows and doors.

If double glazing and film options are not suited to your situation – for instance, if you are a renter or your budget is just too tight – then you can improve the thermal performance of windows with some simple insulation. Windows can be insulated in a number of ways: by covering them with thick curtains or double honeycomb blinds (or similar); even using roller or vertical blinds is better than nothing, but they must be tightly fitted within the window reveal or have pelmets at the top to prevent convective currents circulating, otherwise they will do very little. See Sanctuary 39 for our article on internal window coverings.

Well worth it

Improving the thermal performance of glazing can be expensive, but it is a very worthwhile investment (even if the walls of your existing house are not yet insulated). All new homes and renovations need to meet energy regulations, and efficient glazing is one way you can quickly upgrade a building’s energy performance. High-performing windows may be up to 10 per cent or more of the total cost of renovating or building a home; it is hard to generalise, but industry studies on the homes built by one of Victoria’s biggest home builders showed an average cost payback of just over five years, but it can be as many as 15 depending on your house and climate. For retrofits where windows are being replaced in order to recoup on energy costs alone (without accounting for comfort), Sustainability Victoria’s “Energy efficiency upgrade potential of existing Victorian houses” report found payback periods were much longer. Even assuming a building lifespan of the woefully short Sydney average of 42 years, for many, double glazing is a sound investment, made all the better now that real estate agents are being trained through the Centre for Liveability Real Estate to recognise, value and communicate the potential to home buyers.

If you decide to replace your existing windows and go with double glazing, it is important that you get quotes from at least three suppliers and talk to them about what is right for your home. Remember, what applies in colder climates doesn’t necessarily apply in warmer climes. The orientation of a home and its location on the block will help determine what types of windows are needed. Your Home and WERS are also excellent resources for this. If trying to understand windows and quotes is still making your eyes glaze, seek professional help – it is a specialised area after all.

Also, don’t assume that the same window type and rating is ideal for each room – selecting a window’s ratings for each room can tweak the thermal performance even further. While that may seem like a lot of effort, it can be worth it. Glazing is second only to the base structure for permanence so you may be living with those windows for a long time.


Dick Clarke is principal of Envirotecture, a sustainable building design firm in Sydney and Redland Bay, Queensland. Lance Turner is the ATA’s technical editor and writes for Sanctuary’s sister magazine, ReNew.

Feature image by Peter Mathew; house design by Agnes Nienhaus & Michael Shrapnel, Beachouse Architecture. Read the full profile in Sanctuary 40.

REFERENCES
Your Home
WERS
“Not just window dressing” in Sanctuary 39
“Clear cut: getting the best out of your glazing” in Sanctuary 34
“Double glazing on a budget” in ReNew 135

Gardening with stormwater

Stormwater is rain that runs off the ground or paved areas into stormwater drains that then divert it away from your property. It makes sense to slow this flow of stormwater and direct it to areas where it can soak into the soil and benefit the garden. Slowing the flow reduces stormwater pollution and keeps waterways healthier, while delivering more water to your plants to create a beautiful garden.

The first step is to watch your garden while it’s raining to get an idea of where puddles are forming and where water is flowing across the surface. Are there garden or lawn areas where water is simply running downhill? Are paved surfaces collecting water that could be directed to the garden rather than down the drain? Are there downpipes from the house or garage, or overflow pipes from rainwater tanks that could be redirected to the garden? Be careful not to direct water close to building footings or into your neighbour’s property.

Landscaping can direct water to areas where it can seep into the soil to avoid run off. Plants can be used to help slow the flow of water. Areas called raingardens can be created to take rainwater from roofs or pavements. Or think of your whole garden as a raingarden, and start to make changes that take advantage of stormwater.

You can design overflow points that divert water to drains during intense storms, or use porous surfaces for paving instead of impermeable surfaces so that water can seep through the paving into the soil. With a bigger budget you might even look at installing underground tanks to catch stormwater for later use. You might even be able to store water under permeable pavers.

Many of these ideas come from water sensitive design around new housing developments or in urban landscaping projects, so let’s take a look at how these principles and techniques can be implemented at home.

Swales

Swales can be designed to catch as much rain as possible. Swales are hollows or ridges constructed along the contour of a slope to stall water flow. The water then seeps into the ground for the benefit of the plants.

Swales

In the home garden swales can be subtle variations in the slope that are part of the landscaping without their function being obvious. Hollows can be narrow or several metres wide and can be lined with mulch. Wider swales can even be lawn areas. Similarly, if ridges form the swales they can be grassed or covered with mulch. Plants or landscape features can also help retain and infiltrate the water, or they can be used to extend and enhance your swales. Swales are particularly good for retaining water around trees or deep-rooted shrubs.

Raingardens

Raingardens are attractive landscape features, and serve the function of capturing stormwater so that it seeps slowly into the soil. Common raingardens are ponds or water features designed to take stormwater from overflow pipes from rainwater tanks or direct from downpipes from the roof of the house. A habitat for frogs can even be a raingarden.

A raingarden in an inner city front yard.

A raingarden in an inner city front yard.

A raingarden typically has an overflow point to a stormwater drain for when there is really heavy rain for extended periods. The soil in the raingarden can be protected with mulch or pebbles and the garden should feature plants that can tolerate the soil going from very wet to periodically dry. Parts of the raingarden can be covered with porous paving to allow easy access. When raingardens are next to buildings, waterproof barriers can be used to prevent waterlogging of soil under the building.

The preference is to use rocks or pebbles as mulch in raingarden design, as these don’t float with water flow and clog drains, but like organic mulch, they protect the soil from evaporation and suppress weeds.

Raingarden design.

Raingarden design.

Infiltration tanks

With a bigger budget you could even install underground tanks to harvest stormwater. Tanks can be constructed onsite that allow infiltration of water from the ground above, or surface drains or stormwater pipes can direct stormwater into the tank. This water can then be used to irrigate the garden, or to flush the toilet if it is clean enough.

If you want to use rainwater in the house you will need to keep it separate from stormwater. Stormwater collects contaminants as it flows across the ground, including sediment, organic matter and fertilisers. This may not matter if it’s intended for the garden.

If you want to use rainwater in the house you will need to keep it separate from stormwater. Stormwater collects contaminants as it flows across the ground, including sediment, organic matter and fertilisers. This may not matter if it’s intended for the garden.

The tanks typically include a filter to screen out sediment, leaves and other debris from entering the tank. Initial filtration can happen via swales, raingardens or reed bed filters. When working out whether to install a storage tank for stormwater, consider how much you can exclude contaminants like motor oil from driveways, dog poo, fertilisers and sediment. Prevention is a key to ensuring water quality.

The tank systems best suited to infiltration are modular and consist of a polypropylene liner, geotextile fabric and high density polyethylene assembled to the size of the available space. The polypropylene liner is left off the top of the tank to allow infiltration from above. Soil is then placed over the assembled tank allowing the area to still be used as garden or landscaped; these systems also have enough load-bearing strength to support heavy vehicles. Root guards are needed if large trees are adjacent, and a pump as well so you can use the water.

The tank can be positioned below a raingarden or porous paving to capture water from above. You could use the same tank to take rainwater from the roof and stormwater from the ground, but this will downgrade your rainwater to stormwater quality.

Porous or permeable paving

While you’re probably not going to rip up your concrete driveway to do this, porous paving is something to consider when you’re putting new paving in. Porous paving allows water to seep through into the ground while offering the same stability and function as non-porous paving. Trees or other plants near the paving will benefit from the water.

Porous paving looks much like any other paving except it can filter water to the ground below.

Porous paving looks much like any other paving except it can filter water to the ground below.

Porous paving can be permeable concrete pavers or pebble pavers that look similar to conventional pavers. Or it can be concrete grid paving or modular plastic pavers that form a matrix. Each of these allows water to filter through voids filled with sand, gravel or grass.

Sand or gravel is typically used below the paving to increase the infiltration rate of the water. A gravel layer below porous or permeable pavers can function as a storage tank or it can drain to a separate tank. Stormwater drains can sit below the paving to remove excess water when infiltration areas are full.

Other paving materials include gravel for paths or driveways, as well as some forms of asphalt that allow water to seep through to the ground. Sections of porous paving can be used in conjunction with non-porous paving to allow infiltration in particular areas.


Tips for capturing stormwater in your garden:

  • Look at your garden when it rains to see where surface water is forming puddles or flowing along the ground
  • Landscape your garden to divert run-off to garden beds and areas that can cope with extra water
  • Use swales across slopes to slow and catch water
  • Create a raingarden to capture water
  • Use porous paving in sections of hard pavement to allow infiltration of water.

Featured image: This landscape design enables water to seep into the ground.

WNDTD stormwater chapter - diagrams-1 100pxThis is an edited version of the Stormwater chapter from Stuart McQuire’s book Water Not Down the Drain. Visit the Alternative Technology Association’s webshop to buy your copy

Solar sizing latest: ‘Go big’ with your PV system

Many people ask us what size grid-connected solar system they should get. Traditionally, the ATA (Sanctuary’s publisher) has advised people to consider this carefully. If you primarily want to help the environment and cost is of little concern, it has always made sense to install as many panels as possible, as all their generation displaces electricity from dirty, centralised power plants. But most people have budgetary constraints, so their solar system needs to make economic sense as well as help the environment. To achieve this, we’ve previously recommended that people size a solar system based on their electricity consumption and maximise their other opportunities, such as energy efficiency. However, things have changed.

TWO BIG CHANGES

Solar system prices

The past five years have seen significant price reductions, especially for larger solar systems. Prices vary with component quality and location, but on average a 5kW solar system now costs around $6200 according to Solar Choice’s residential price benchmark data. If we compare a 5kW system to its smaller 2kW cousin, since August 2012, the larger systems have halved in price, while the smaller ones have dropped by only a quarter.

Larger systems have always enjoyed economies of scale compared to smaller systems, because while the installer is on the roof it’s relatively easy for them to add more panels. One difference now is that the price of solar panels has fallen faster than other components. The industry has also become more familiar with larger systems, as they are now more frequently installed than small ones. [Keep an eye on the STC solar rebate which goes up and down and has recently become volatile.]

Feed-in tariffs

The Victorian government recently increased the solar feed-in tariff to 11.3 c/kWh, roughly double their previous level, and IPART in NSW has recently recommended a similar change in NSW. These changes are primarily due to wholesale electricity prices in the eastern states roughly doubling over the past year to around 10c/kWh. We expect other states to follow suit, as feed-in tariffs below the wholesale electricity price are clearly unfair to people with solar. (In WA, a similar rise in wholesale rates hasn’t occurred, but prices might still rise due to the state government winding back its subsidy of electricity prices.)

WHAT THIS MEANS FOR SOLAR SYSTEM SIZING

Given these changes, if you’re planning a solar system, is it worth it to upsize from, say, 2kW to 5kW?

The extra panels will be relatively cheap but more of their generation will be exported, which doesn’t help the economics. For example, depending on household consumption, a solar system rated at 5kW might export 80 per cent of its generation. Electricity exported to the grid only earns the feed-in tariff, ranging from 5c to 14c per kWh, depending on your location and electricity plan. Solar electricity used on-site, rather than exported, saves you paying the grid tariff, typically around 20c to 35c per kWh.

Surprisingly, our modelling of the economics found that a 5kW system now has a shorter or equivalent payback time to the 2kW system. We studied the economics by simulating a large number of scenarios in half-hour intervals for a whole year using Sunulator, ATA’s free online solar feasibility calculator.

Our primary economic measure is payback time, the number of years until bill savings recoup the installation cost—the fewer years the better. Payback times shorter than 10 years are generally considered attractive to solar customers, as the system is likely to pay for itself before any significant expenses, such as replacing the inverter. The panels should last at least 20 years, so cumulative bill savings are large, especially for a larger system.

To do the modelling, we assumed a feed-in tariff of 11.3c/kWh in Victoria and in other states a doubling of feed-in tariffs from current levels, phased in over the next five years. We considered common grid tariffs in each capital city, for a variety of household consumption profiles, along with likely tariff increases (we used AEMO’s retail tariff forecasts, but since they were based on Hazelwood closing in 2020, which happened this year, we pulled them forward by three years; this allows for annual tariff rises between 1.5 per cent for Queensland and 3.4 per cent for Tasmania). Panels are assumed to be north-facing with a 20-degree tilt. Our analysis also includes panel degradation over time.

RESULTS: BIGGER IS BETTER

Figure 1 shows the payback period for a stay-at-home family using 23kWh/day on average, on a flat tariff. In no location did a 2kW system pay back quicker than a 5kW one. We also ran scenarios for 3, 4 and 6kW systems, and found these obeyed the same trend.

Figure 1 shows payback time by location and solar system size; it includes 2 kW (blue bars) and 5 kW (red bars). This is calculated for a stay-at-home family using 23 kWh/day on average and on a flat tariff. In no location does the 2 kW system (blue bars) have faster payback.

Figure 1 shows payback time by location and solar system size; it includes 2 kW (blue bars) and 5 kW (red bars). This is calculated for a stay-at-home family using 23 kWh/day on average and on a flat tariff. In no location does the 2 kW system (blue bars) have faster payback.

The Northern Territory is a special case as solar installations are particularly expensive, but this is counteracted by a relatively generous feed-in tariff, equal to the import tariff. Bigger is better here too!

We also ran scenarios, including the payback for different households in Sydney on a flat tariff. For a 5kW solar system, payback time varies from four to eight years depending on consumption profile. Households with higher consumption achieve payback more quickly. Again, there are no cases in which a 2kW system pays back more quickly than a 5kW system.

LOW-CONSUMPTION BUILDINGS GAIN TOO

With feed-in tariffs at the new higher levels, a solar system can now be economic even if it exports all its generation. For example, an export-only 5kW system in Melbourne should generate around 700kWh and earn $790 per year. If the system costs $6400, on the simplest calculation it achieves payback in less than nine years. Because of this, low-consumption buildings such as holiday houses and storage sheds have become a new market for solar systems.

WHAT IF TARIFFS DON’T RISE?

If you install a big solar system based on future rises in feed-in and import tariffs, there is a chance this might not eventuate, causing bill savings to be less than planned and delaying payback. We think this risk is low. Future prices are notoriously hard to predict, but the current wholesale electricity price appears to be the ‘new normal’.
Previous low wholesale prices were only possible because most energy was generated by old coal-fired power stations that had paid off their financing costs. Any new-build generation won’t have that advantage.

Over the next year or two, new generation is expected to re-balance supply with demand and ease wholesale prices. On the other hand, as wholesale prices reduce, financial pressure on generators will hasten closure of the next ageing coal-fired power station. We may see a saw-tooth trend with steady price declines punctuated by periodic upward jumps. As usual, the big unknown is government policy.

Even if tariffs don’t rise, our modelling still suggests a big solar system has good economics.

CONSTRAINTS ON BIG SOLAR SYSTEMS

If bigger is better, how big should we go? Roof space is an obvious constraint. As noted above, most people have budget constraints and have to prioritise their spending. Don’t ignore other investments that may pay off even quicker, such as insulation, gap sealing, window shading, LED lights and efficient appliances.

Electricity distributors limit the size of solar systems connected into their grid. If you’ve got a normal residential single-phase connection, solar systems up to 5kW in size are usually no problem. Going larger often requires extra paperwork and may not be allowed. One good strategy is oversizing, for example, connecting 6kW of panels to a 5kW inverter. The distributor treats this as a 5kW system, as that’s its maximum power output. Another option is to install a three-phase electricity supply, which would normally support a 15kW solar system. However, upgrading your electricity supply involves additional cost.

GOOD FOR THE ENVIRONMENT

These results are good news for the environment. Economic and environmental priorities have aligned; for both, it’s generally better to ‘go big’ with your solar system. However, there may still be competing demands on your capital. In particular, when building a home it’s best to prioritise items that are difficult to install later, such as efficient windows and wall insulation. If you have to make such a choice, it may be wise to delay the solar installation until funds become available.

Andrew Reddaway is an Energy Analyst at the ATA. He has extensive experience in the analysis of electricity and gas networks including the impact of solar photovoltaic generation. Get the full ATA report.

Material benefit: specifying eco building products

Mullum Creek and The Cape are two of a growing number of housing developments aiming to raise the bar on thermally efficient, eco living. To drive sustainable practices, Tony O’Connell, director of TS Constructions and builder of The Cape, helped to create mandatory design guidelines for anyone buying into the estate. Intended to assist homeowners, architects and building designers to meet the estate’s ESD criteria, the guidelines include a list of acceptable building materials to make the design and build process easier.

Tony O’Connell says that his initial building materials list took 12 months to compile, and several years later it’s still under review as new products come to market. Among other things, the list specifies that any concrete should include fly ash and recommends any timbers sourced should have independent certification. LOSP (light organic solvent preservative, or equivalent) preservative treatment of timbers is also recommended instead of CCA (chromated copper arsenate).

Building designer Dick Clarke (in his inimitable style) says not specifying sustainable and healthy building materials is “gross stupidity and irresponsibility”. Unsustainable materials off-gas, play on your conscience – knowing their procurement or manufacture was unethical – and they just don’t give you that same sense of joy as better alternatives.

But few homeowners have access to builders who have spent years curating a specification list. Seeing through the green wash and choosing the best materials isn’t easy, or more people would do it! Instead most do what they can, learning as they go, or rely on the advice of specialists or product manufacturers. Unlike the energy star ratings on appliances which make it easy to compare products on at least one major metric, there isn’t a simple, market-wide scheme available for building materials. And there is seemingly little interest from government to make this happen.

Take engineered timber, for example. Engineered timber that you might use for structure, flooring and cabinetry is made from derivative wood products, adhesives and varied finishes. Drilling down into each component – how and where was it sourced; how was it manufactured; the energy-intensiveness of the production process – just isn’t realistic.

Making final decisions on which building materials to specify will depend on a range of factors. Light-earth construction was chosen for this 'sustainable house in progress' near Daylesford, due to its insulating qualities and local availability. Image: Mara Ripani

Making final decisions on which building materials to specify will depend on a range of factors. Light-earth construction was chosen for this ‘sustainable house in progress’ near Daylesford, due to its insulating qualities and local availability. Image: Mara Ripani

Which eco-material listings to trust?

Dick Clarke, who has his own business Envirotecture and is editor of How to rethink building materials: Creating ecological housing for the designer, builder and homeowner, says the best thing to do is to trust the two main certification schemes – Good Environmental Choice Australia (GECA) and Global GreenTag – while cultivating a healthy scepticism of other accreditation schemes, and to use the online green materials database, Ecospecifier. If these tools don’t provide a clear choice, he says, the decision may come down to “making the least-worst choice”.

For Elizabeth Wheeler of Future Focused Buildings, who specialises in helping homeowners wade through the materials specification process, this “least-worst” choice varies not only per product, but per person. She advises homeowners to develop their own criteria by asking themselves what they consider to be important before they start their research process. Some people might prioritise recycled content in their products; for others, it might be end-of-life disposal, product re-use, off-gassing or social justice.

From there, it’s really a process of doing your homework. For example, “If you are concerned about how your timber is sourced, you might read up on accreditation systems like FSC and PEFC,” she suggests. “You might also interrogate some of the important-looking but actually meaningless logos and slogans that appear on many company websites.” She cautions homeowners to understand that smaller producers often can’t afford accreditation. “There are businesses that have really good products but just can’t afford to, or choose not to, spend money on formal accreditation. So don’t discount a business just because they don’t have accreditation. But certainly ask them why they don’t.”

Emailing producers with very specific questions related to your concerns will not only enable you to keep track of information but help you to compare products. And when investigating online Elizabeth recommends seeking out “the debates and discussions, not the marketing materials”.

Rammed earth, particularly when sourced on-site or nearby, is not only beautifully textured but is low in embodied energy too. This home in Margaret River, WA, designed by Paul O'Reilly prioritises materials that need little maintenance. Image: Douglas Mark Black

Rammed earth, particularly when sourced on-site or nearby, is not only beautifully textured but is low in embodied energy too. This home in Margaret River, WA, designed by Paul O’Reilly prioritises materials that need little maintenance. Image: Douglas Mark Black

For homeowners without the time, knowledge or resources to navigate the materials specifications process, it can help to get professional assistance, either through your builder, designer or architect, or through a specification professional. Regardless of who is doing the product selection, it’s vital that they understand and respect your concerns, and that roles and responsibilities for materials and product selection are agreed by all parties.

Sourcing green building materials ideally should be a team effort according to Dick Clarke, partly because it’s practically impossible for any one person to stay on top of the myriad existing and new products on the market, and partly because it achieves a better result in the short and long term. “Homeowners who have been involved in the selection of materials own those decisions, they maintain and look after the materials, and they promote them in those BBQ conversations,” he argues.

“I also think it’s very important for people to understand that documenters and builders have a legal responsibility for many of the materials used in a build,” says Elizabeth. “They have to be convinced that the material being used is fit for purpose, so ultimately, it is their call.”

Promoting these products isn’t only for BBQs. Tony O’Connell found that the process of putting the list together expanded his team’s knowledge base and that of their preferred list of subcontractors. “We also went out to a large number of manufacturers and suppliers and asked them to help identify suitable products to evaluate.”

Other materials used in The Sociable Weaver's 10 Star home include recycled brick walls painted with a coat of natural no-VOC paint, alongside FSC plywood panelling with a natural seal applied. All concrete must include a flyash component. Image: Dan Hocking

Other materials used in The Sociable Weaver’s 10 Star home include recycled brick walls painted with a coat of natural no-VOC paint, alongside FSC plywood panelling with a natural seal applied. All concrete must include a flyash component. Image: Dan Hocking

Elizabeth challenges homeowners to think about products on a deeper level: “Do you want to buy from a company that manufactures products that are lower-impact alongside others that have a huge detrimental impact, or support a smaller business that makes only lower-impact products?”

This question might seem like a no-brainer, but sometimes when extra effort and/or expense are involved, decisions aren’t always clear-cut. We all need to establish our own personal line in the sand and personal choices are only one of several ways to push for more sustainable buildings. “We also need to ask ourselves why high-impact products are still available in the marketplace,” says Elizabeth. “Some products just shouldn’t be allowed to exist, when there are better and less impactful alternatives available. A lot of decisions that rest with the market are actually systems issues. Our activism is as important as our everyday choices.”


Resources

Good Environmental Choice Australia
Global GreenTag
Ecospecifier
FSC certification
Mullum Creek
The Cape


Verity Campbell is a communications consultant, freelance writer and trainer with extensive experience working with architectural and design firms.

Feature image: This groundbreaking 10 Star home at The Cape, designed by The Sociable Weaver, is clad in FSC-certified, radial sawn timber that has been left untreated to naturally silver with age in order to reflect the coastal palette of the surrounding landscape. The development’s design guidelines include a comprehensive and evolving list of recommended building materials, making it easier for homeowners to choose responsibly. And, you can visit this house on Sustainable House Day! Image: Dan Hocking