Michael Green

Writer and producer

Green renovations

In Architecture and building, The Age on

Whether you’re renovating for resale, rental or long-term liveability, every signal has turned green.

BY May next year, the state government will increase the residential energy efficiency standard from five to six stars.

The star rating system applies to all renovation projects that require a building permit, but varies depending on the size of the alteration. For larger additions the whole house must comply, while for smaller changes only the new part must adhere to the rules.

The state government will also soon phase-in compulsory eco-scorecards at the point of sale and lease. With more and more people seeking energy efficient housing, it’s wise to renovate green to make sure your home doesn’t fall behind.

Here are some principles to follow:

Orientation, glazing and thermal mass

“The primary aim of the renovation should be passive solar performance,” says architect Mark Sanders from Third Ecology in Geelong. “That means getting living areas facing north.”

If your block has a north-facing backyard (or, on a wide block, a north-facing side), you’re in luck.

The task is more difficult if you want to extend to the south. One solution is to design a courtyard between the old and new parts of the home, thereby creating a northerly aspect and allowing the sun into the extension.

Mr Sanders says it’s crucial to combine smart orientation with appropriately shaded windows that allow the sun in during winter, and block it out over summer. “We also try to incorporate a concrete slab to the north, so we’ve got thermal mass to store and re-radiate the heat,” he says.

One result of the step up to higher building efficiency standards may be that designers pay closer attention to the placing and quality of windows. To lift the overall performance, choose fewer, smaller or better windows for the southern and western sides of your home. “It’s preferable to use double glazing,” Mr Sanders says, “or single glazing with decent window coverings.”

Insulation

Mr Sanders recommends householders commission a star rating of their home early in the planning stage. It’ll help identify weaknesses in the performance of the existing building fabric, and pinpoint how they can best be remedied.

“It’s not a compliance requirement, but we just think it’s an important part of a holistic review,” he says.

He used the process for his own house, a Victorian-era home he lifted from zero to six stars. “That meant insulating the walls and floors and doubling the insulation in the ceiling,” he says.

Wall insulation is essential to achieve high star ratings, and a renovation can provide a rare chance to install it relatively cheaply. Mr Sanders’ method was to cut out a section of plasterboard in the middle of the walls. “We slipped insulation up and down and re-plastered without touching the cornices and skirting boards,” he says.

Heating, cooling and ventilation

There’s a wide range of heating options, and the one you choose will depend on the your house. But according to sustainability consultant Malcolm Wilkie, zoning is non-negotiable. “Heat the living room and close off the areas you don’t need. Bedrooms and hallways don’t need to be heated.”

Mr Wilkie says air conditioning isn’t necessary in a house that has been renovated to provide good orientation, shading and insulation. “If you’ve got the house right, all you need is a little bit of air movement on really hot days, and fans will do that.” Be sure that your windows can be opened for cross-ventilation at night or when a cool change comes through.

Lighting

When it comes to lighting, Mr Wilkie has one golden rule: “Don’t install low-voltage halogen downlights.”

Despite their popularity, halogen downlights are terribly inefficient, expensive to run and need gaps in ceiling insulation to reduce fire risk.

He suggests pendant fittings or wall-mounted up-lights instead. “It’s better to use bright task lighting only where you need it, like over a reading chair, and not to flood the whole room with light,” he says. “It’s more creative and creates a much nicer ambience.”

Mr Wilkie also recommends that renovators let in as much natural light as possible. With a combination of skylights and roof windows, he says, “during the day you shouldn’t need to have any artificial lighting on at all.”

Water

If you want to save water, time and money, your pipes and plumbing mustn’t be an afterthought. Stuart McQuire, author of Water Not Down the Drain, advises early planning for water tank placement and use.

“If you’re re-doing spouting or guttering, direct it towards a place where you can fit the tank, and get as much of your roof going there as possible,” he says. “Sometimes a renovation opens access briefly, so you might need to order it before you put the frame up.”

Rainwater can be used for the garden, or connected to toilets, the laundry, hot water, or even the whole house – depending on how much you can collect.

“If you want to water your garden, get the biggest tank you can fit and afford. When there’s an extended dry spell, that’s when you’ll appreciate it,” Mr McQuire says. “But if it’s just for toilet flushing or even for the laundry, you don’t need a huge tank.”

Even if you aren’t installing tanks or connecting toilets and greywater immediately, a little extra plumbing up front will leave your options open – and save a lot of hassle later on.

“If you are renovating the bathroom, put the plumbing in so you can run rainwater to the toilet. It’s a lot harder to do once the walls and floors are there. The same thing applies to greywater, because it might be impossible to do later without pulling your bathroom and laundry apart,” he says.

When you choose fittings for the bathroom, laundry or kitchen, look out for the Water Saving and Efficiency Labels and Standards (WELS) scheme. The labels include a star rating – up to six stars – and a flow rate in litres. Good fittings will save you hot water, and therefore, energy too.

For even better hot water efficiency, Mr McQuire recommends householders opt for a solar water heater, if they’ve got a roof that isn’t too shaded by trees or neighbours.

For more tips, see the Your Home Renovator’s Guide. 

Contact Malcolm Wilkie.

House energy ratings

In Architecture and building, Environment on

IF you’re building, buying or renovating, there’s now more reason than ever to make your home as efficient as you can. Here’s a guide to house energy ratings and regulations, and the returns for going green.

House Energy ratings

House energy ratings are a measure of the thermal efficiency of a dwelling. Basically, the stars tell you how comfy the home will be throughout the year.

So how are they figured out?

Energy assessors plug the details of your plans, or existing building, into a software program such as FirstRate5, AccuRate or BERS Professional. The programs, accredited by the Nationwide House Energy Rating Scheme (NatHERS), analyse the home’s layout and orientation, and the construction of the roof, floor, walls and windows.

This information is matched with the local climate to calculate how much heating and cooling you’ll need to stay comfortable every day of the year. Homes can score between zero and ten stars. At zero stars, the building does next to nothing to protect against the temperature outside; at ten, it will be nice and snug without any artificial heating or cooling. A five-star home is good, but far from outstanding.

The ratings are one way to comply with the minimum standards for new buildings set out in the Building Code of Australia. It’s up to the states and territories to apply those standards – and they tend to do it haphazardly, with their own variations.

The New South Wales government has sidestepped star ratings altogether. Its planning tool, BASIX, contains caps on energy and water use as well as environmentally sustainable design considerations such as location, materials and fittings.

Last year, state and federal governments agreed to lift the residential energy efficiency standards from five to six stars (or equivalent), and bring the changes into effect by May 2011.

Six star

Six-star homes need one quarter less energy than five-star homes to stay comfortable, says Wayne Floyd, president of the Association of Building Sustainability Assessors (ABSA). “And of course, that reduction translates into lower utility bills.”

Despite yelping from the building industry about price hikes, Floyd argues that the higher performance can be reached at little or no extra construction cost. “Orientation is the key factor. If the house is designed correctly for that block of land, it can be cost neutral,” he says.

“We’re starting to see houses with bedrooms to the rear and living areas to the front, because that gets the greatest solar access. I’ve looked at projects that achieve over six stars with standard insulation and no double glazing, because they’re oriented and designed correctly.”

Poorly oriented homes can still reach six stars, but they need top-quality windows and insulation. Even in those cases, Floyd says, “the expense is very minor relative to the total cost of the house.”

So the higher standards might not cost much, but will they make a big impact?

Because the new regulations don’t take into account house size, appliances and behaviour they won’t necessarily reduce our overall household energy consumption.

New houses are much larger than in decades past, which means they gobble more energy, materials and consumer items, and spit out more waste, all of which take energy. Likewise, our habits around the home have a drastic effect on the amount of energy we consume.

Damien Moyse, energy policy officer at the Alternative Technology Association, says that in an international context, the new regulations are far from ambitious. “There are many regions, particularly in Europe, which require the equivalent of seven stars or above,” he says. “The UK has a program for zero net carbon homes by 2016.”

According to Moyse, in order to reduce the carbon emissions from housing, we must target existing homes. “The real trouble with the star rating scheme is that it’s generally for new buildings,” he says, “and new buildings are a very small percentage of our housing stock.”

Mandatory disclosure

The good news is that state and federal governments have also agreed to a measure that could lift the energy efficiency of existing houses.

Under new ‘mandatory disclosure’ rules, homeowners and landlords will be required to declare the energy, water and greenhouse performance of a house when they put it up for sale or lease. That means buyers and renters will be able to compare the environmental impacts and ongoing costs of different homes before they sign on the dotted line. “It will be very good because it focuses on the built environment, not the ‘to-be-built’ environment,” says Wayne Floyd.

The rules were scheduled to be phased in from May 2011, beginning with energy efficiency, but so far no details have been finalised. “It’s up to the individual states to adopt it, and each state is working on its own version. I feel that it will be a two or three year process,” Floyd says.

Moyse argues that although the added transparency will encourage more people to retrofit their dwellings, the changes could have gone further. “Mandatory disclosure just provides information,” he says. “You also need minimum standards to force landlords or homeowners to upgrade their properties.”

The growing market for green homes

Buyers are already getting the message, especially in the ACT, where mandatory disclosure at the point of sale was introduced in 1999. A study for the federal government found that in 2005 and 2006, lifting the energy rating of a median-priced house in the ACT by just half a star added about $4,500 to its value.

The study shows that, depending on the specifications of house, the cost of adding stars can be far lower than the payoff when it comes to selling.

Danielle King has just founded Green Moves, a sustainable real estate listing website. She says estate agents are split on the importance of eco-friendly features. “Some think that greening up doesn’t make a difference. Others believe it’s becoming more and more significant.”

With tougher regulations coming in, King says it’s unwise for people not to focus on energy efficiency, especially if they’re considering a renovation. “Like it or not, sustainable homes are the future of the real estate industry.”

She points to ‘green belts’ in the inner suburbs of our cities, such as Brunswick in Melbourne, where “properties with sustainable features have been selling at between $80,000 to $100,000 more than equivalent properties without them”.

“My view is that homes with good energy performance and lower greenhouse gas emissions will enjoy a noticeable increase a market price. It’s already happening regardless of mandatory disclosure and six star being in place.”

Case study: Rate as you renovate

When Peter Nattrass and his family decided to renovate their 1920s bungalow in the Adelaide suburb Prospect, they decided to give energy efficiency pride of place.

In his job as a development assessment planner and sustainability advisor, Nattrass had observed that energy rating is usually an afterthought, used only for council compliance. “People think about energy efficiency too late and end up rushing to fix something that’s fundamentally broken,” he says.

The Building Code of Australia is a model code for new buildings. When it comes to extensions, each state and territory applies the rules differently – for details, you’ll need to contact your local authority. Generally speaking, the new portions of the dwelling must meet the code’s specifications, but it isn’t mandatory to lift the rating of the whole home.

“We wanted our extension to lift the performance of the rest of the house,” Nattrass says. “We instructed the architect from day one that we wanted a passive solar design and that we would be having it rated as we went.”

He estimates that his original house would have scored about two stars. Based on the architect’s extension plans, energy assessors Sustainability House rated the home at just below five stars.

“They thermally modelled the whole house and that picked up the weaknesses in our existing home. We then tweaked the specifications,” he says. The family was able to compare the costs and benefits of measures such as ceiling and cavity wall insulation, double-glazing and a planned reverse brick veneer wall.

The process reduced their projected energy needs by another quarter, for very little cost – under $500 for the initial assessment and advice. “We lifted the whole house up to six star and went for the best bang for our insulation bucks,” Nattrass says.

The experience has given the family extra comfort, both physically and financially. “One of the key drivers for us was avoiding the risk of underperforming compared to new homes built to the six star requirements. If you don’t bring the rest of the house up, you could end up disadvantaged in the market when you sell.”

Published in Sanctuary Magazine 12.

Lower-carbon concrete

In Architecture and building on

Concrete is ubiquitous. According to Dr Peter Duxson, chief operating officer of eco-concrete company Zeobond, it’s the second most used commodity in the world, behind only water. “Everywhere there is human activity, there is concrete being used. It’s versatile and cheap,” he says. “It just turns out that the base ingredient that makes concrete go hard is bad for the environment.”

Concrete is made up of sand, rock and water, bound together with cement. Conventional concrete uses Portland cement and although it comprises only 10 to 15 per cent of the total product, it accounts for about 70 per cent of its carbon footprint.

The high emissions come from burning limestone to create lime – from both the energy required to heat the kilns and the chemical reaction in which limestone releases carbon dioxide. “One kilo of CO2 is emitted per kilo of cement,” Duxson says. “So every concrete truck equals about two tonnes of CO2 in cement.”

The material’s saving grace is its usefulness as thermal mass in appropriate solar passive design – it can help to even out day and night time temperatures. According to Riccardo Zen, from Zen Architects in Melbourne, carefully placed high-density materials are essential to cut the energy needs of homes in temperate and cool climates. “It’s very hard to eliminate heating and cooling unless you have some form of thermal mass,” he says.

An exposed concrete slab floor is a classic example of thermal mass. Positioned in front of windows in a north-facing living room, the slab receives direct sun in winter. It absorbs the solar radiation and warms the house into the night. With appropriate shading, the sun won’t hit the concrete over summer, so the chill of the concrete will help the home stay cool.

Even so, given that concrete accounts for about five per cent of global carbon dioxide emissions, the race is on make lower-carbon concrete.

The simplest way to do so is to substitute a proportion of the Portland cement for other products. Fly ash and slag (by-products of burning coal and smelting iron ore, respectively) can comfortably replace over one-fifth of the cement content without adversely affecting the quality of the product.

Boral’s Envirocrete is available with either 30 or 60 per cent less Portland cement – the difference made up with fly ash, slag and chemical admixtures. The company also sells Envirocrete with one-fifth recycled crushed aggregate. Although it saves virgin resources, it doesn’t significantly reduce the carbon dioxide emissions of the product.

Duxson’s business, Zeobond, makes Ecrete, a kind of concrete that completely replaces Portland cement with fly ash and slag. Known as a geopolymer or alkali-activated concrete, Ecrete produces two-thirds fewer carbon dioxide emissions than the conventional product. It uses other chemicals to kick-start the binding process and ensure the curing time is fast.

The first Ecrete supplier is located in Melbourne’s north-eastern suburbs, but Duxson anticipates that it will soon spread interstate. The product is also available in pavers and pre-cast panels. “The cost premium is between 10 and 15 per cent, but as we get to scale, we expect that price to come down quite significantly,” he says.

Magnesia-based concretes are another kind of lower-carbon concrete. Tasmanian company TecEco sells blended cements that include reactive magnesia as well as Portland cement and waste materials. When used in permeable concrete blocks, pavers and pavements, the company’s Eco-Cement absorbs carbon dioxide over the lifespan of the material.

This article was published in Sanctuary Magazine.

Solar thermal heating and cooling

In Architecture and building on

HEATING and cooling churns through nearly 40 per cent of Australian household energy use. Energy prices are set to hit ever-higher levels, so the more efficient a temperature control system is, the more attractive it looks – almost day-by-day.

There’s a growing industry selling units that use the sun’s free energy to ventilate, warm and even cool your home. They can also improve indoor air quality by reducing humidity, moisture build up and mould. Broadly, the systems fall under the banner of ‘solar thermal air heating and cooling’.

So what’s commercially available and how well do they work?


Roof space systems

These units work by moving the air in our roof cavities. When the sun strikes the roof, it warms the air below – just as cars get stuffy on clear days even if it’s chilly outside. For heating in wintry weather, roof space systems pump that warmer air inside the home. To help with cooling in summer, some units can extract the hot air from the roof during the day, and also, blow cooler outside air into the house overnight – useful if you’re worried about security or the noise of open windows.

There are two types of roof space solar collectors. One kind, sold here by businesses such as HRV, Solectair and Smart Roof, uses the whole roof cavity as a collector. The intake is near the top of the space, where the warm air rises. A fan sucks the air through a filter and ducts it into the home.

The second kind of technology, offered by Smart Roof in its Smart Breeze system, is suitable for metal roofs. It captures heat in the gap between the roof sheet and a layer of insulating foil or sarking underneath. The warm air rises to the apex of the roof cavity, where it’s nabbed and whisked into the home (using a solar-powered fan). “The ribs act as ducts and we seal the ridge so the air can’t escape,” says Smart Roof CEO Robert Semmel.

He says that the system can significantly reduce bills, but won’t do away with other sources of temperature control. “Our aim is to reduce heating and cooling by up to 40 per cent, not to replace it. If you’ve got a miserable, wet day there’s no radiant heat and on really hot nights there won’t be any cool air to bring in. But those are extremes.

“If the sun is out on a 15 degree day, we get temperatures up to 40 degrees [in the roof]. When cloud cover comes over, we get 30 degrees. There’s a lot of wasted energy we can use,” Semmel says.

According to energy efficiency expert, Adjunct Professor Alan Pears from RMIT University, the catch is that our roofs aren’t very good solar heat collectors. “A roof space can be described as an unglazed, very leaky solar collector, with a substantial proportion of its area facing the wrong direction,” he says. “So in that sense it’s not very efficient.”

But all is not lost. “On the other hand, it’s a very large area, so you can collect quite a lot of useful heat, especially in mild seasons,” Pears says. Light-coloured roofs with insulation directly underneath will collect much less warmth than a dark roof without insulation. Similarly, the roofing material will influence the way the systems function. Metal roofs heat up (and cool down) quickly, whereas the thermal mass in tile roofs means they take longer to warm, but stay hotter for longer in the evening.

If you’ve ever crawled into your roof space, the idea of pumping that air into your home might make you splutter. But Pears argues the air near the top of the roof space is likely to be no worse than other sources of ventilation in our homes. “The air coming through windows or under doors is unfiltered and often highly polluted,” he says. “In any case, most roof space systems offer a filter. The filtration systems available are very impressive, as long as you buy a good one and maintain it properly.”

Solar air collectors

A solar air collector consists of a clear plastic or glass-fronted panel that uses solar radiation to heat air, like the way a solar hot water unit heats water. The panel is mounted outside the house, either on the roof or a wall. A fan (usually solar-powered) blows the warmed air into the house. For cooling at night during summer, it may also blow cooler outside air into the home.

In Australia, a variety of solar air collectors are available, including products from SolaMate, Solar Breeze, Sun Lizard and Solar Venti.

Arne Hachmann’s business, Global Eco and Environmental Solutions, sells Solar Venti units. If you want to ventilate your home, he advises that a 3 square-metre panel will suffice for an energy-efficient 250 square-metre home. If heat gain is your priority, he recommends one unit of that size per 100 square metres of floor space.

He says the Solar Venti warms air to about 35 degrees above the outside ambient temperature. “If you have a sunny 15-degree day, you would expect to get 50-degree air ducted into your house for free, at a rate of about 200 cubic metres per hour.”

Pears has a SolaMate prototype solar air collector installed on his Melbourne house. The panel is three square metres and feeds into his hallway and living room. “In reasonably sunny winter weather, it’s enough to make a significant difference to the temperature of my fairly small and well-insulated home,” he says. “It makes a bigger difference in spring and autumn when the house cools down a lot overnight but the weather outside is pleasant.”

He warns that householders should buy big units if they want to collect a lot of heat. “Most systems are not very large, so they may not collect a lot of energy, especially on cloudy days. Also, if they’re single glazed, their efficiency may not be very good in colder weather.”

He says that solar air heaters work better in winter if they’re steeply sloped to face the low sun. “It may also be preferable to angle them slightly east of north, so they warm up the house more in the morning when air temperatures are lower and the building interior is colder.”

Cost and benefit

According to the Solar Thermal Air Heating and Cooling Association, both kinds of systems start from about $2,500 installed, with an average price of $4,500 installed. It estimates that the return on investment will vary from two to ten years, depending on the house and the habits of the householders.

Dr Bob Fuller, a low-temperature solar thermal researcher from Deakin University, is not yet convinced of the effectiveness of the systems. When it comes to heating, “there’s a big mismatch – the resource is low in winter when the demand is high,” he says.

Another problem is that there is no Australian Standard for this technology. “There needs to be some independent modelling and testing,” Fuller says. He maintains that as a first step, householders are best served by improving energy efficiency in other ways. “I would spend the money on conservation – on better insulation, curtains, and shading in summer.”

Certainly, these products should not be considered as a replacement for appropriate solar passive design, either when building from scratch or retrofitting. Semmel, from Smart Roof, says that if sun is pouring through a bank of west-facing windows, a ventilation system can only do so much. “In that situation, stopping heat getting in from the ceiling is not your major concern.”

For heating and cooling, the systems are most useful in a well-designed and insulated building. Where a home has thermal mass, the heavy materials will store the extra warmth and ‘coolth’ provided by the units. In a well-sealed house, the systems not only provide fresh air securely and noiselessly, but also, less of the airflow will escape through gaps.

Both Fuller and Pears note that there is a trade-off between the temperature and the volume of the air coming into the home. That is, the systems take time to heat the air, but if the fan runs too slowly, then not enough will enter the home to make any difference. “In some cases, because of other heat losses or gains, to maintain a temperature you might need enough volume for up to ten air changes per hour,” Fuller says.

Pears says it’s vital that solar air collectors include a high-capacity, variable-speed fan that can adjust flow rates according to the heat of the air in the panel. Likewise, the ducting on both kinds of systems should be good quality, and as short and straight as possible, so as not to reduce airflow.

Some systems, complete with clever thermostats, can adjust and make the tricky decisions for you. Set to function automatically, they will sense the temperatures in the collector, as well as inside and outside the home, and heat or ventilate as required.

But even the best designed systems, says Fuller, will not always be able to provide enough warmth and airflow to maintain the temperature inside the home. So it’s important not to expect miracles. These are supplementary systems – they won’t do the job all by themselves. 

Published in Sanctuary Magazine

Windows

In Architecture and building on

Windows might be transparent, but they’re complex. Good windows well placed will help keep your home comfortable all year round. Bad windows in the wrong place will cost you dearly.

In a typical insulated house, they cause more heat gain or loss than any other part of the building fabric. While they’re expensive up front, they’re also an investment in the resale value and day-to-day comfort of your home.

So which windows should you choose? There are hundreds of products and combinations to consider, from the glazing, frames and coatings, to the size, shape and location. The Window Energy Rating Scheme website lists detailed ratings of over 40,000 products.

Two years ago, Alan Kerlin designed his sustainable home in Canberra. Afterwards, he established a consultancy, Solar Flair, to help pass on what he found out. When he was researching windows, he found good advice hard to come by. “It’s a difficult area, but it’s easier if you understand some of the basics behind the science,” he says.

Heat transfers in different ways – for windows, you’ll need to consider conduction and radiation. Conduction refers to the ambient warmth that passes through the glass and the frame. A window’s conduction is measured by its U-value. The lower the U-value, the better its insulating qualities, and the better for your electricity bill.

Radiation, in contrast, refers to heat transferred when sunlight passes through the glass, hits something and warms it up. It is measured by the window’s Solar Heat Gain Coefficient (SHGC); the higher the SHGC, the more radiant heat it lets through.

Passive solar design

Armed with this knowledge, you need to consider the weather where you live and the design of your home. Most Australians live in climates where we want to draw in extra warmth during the cold months and shut it out throughout the hot months. With careful consideration, your windows can help this happen – together other elements of passive solar design, such as shading and orientation.

In Canberra, Kerlin designed his home with a bank of glass to the north – the sun streams in throughout winter, but eaves and shading block the direct rays in summer. Small windows to the south, east and west help reduce the solar access when the sun is low in the sky and passes below the awnings. “But remember: it all depends on where you are living,” he says. “In northern Australia, you never want sun hitting your glass at all.”

Insulating glazing units (IGUs)

No matter your location, there is one constant: double glazing is always preferable to single. For now, nearly every Australian home has single-glazed windows. “They’re like a thermal wound in the building envelope,” says Gary Smith, from the Australian Window Association.

Double and triple glazed windows – known as IGUs – help heal the wound. “Standard double glazing can reduce conducted heat transfer by about half,” Smith says. Triple glazing is common in Europe and North America, but rare here. The window units weigh and cost more, but provide extremely low U-values and excellent sound proofing.

Within an IGU’s frame, the panes of glass are held apart by a spacer. A wider gap gives better insulation – 12 mm is regarded as the best. Likewise, an IGU will prevent even more heat transfer if the cavity is filled with an inert gas, such as argon, rather than air. “With argon, you get about a 15 per cent improvement in U-value,” Smith says.

IGUs also perform strongly in bushfire attack conditions. “Double glazing works really well in the bushfire tests because the insulation barrier stops the radiant heat coming through the glass,” he says. This year, all states and territories will introduce a new standard for windows and doors in bushfire prone areas. So far, few products have been tested to the top levels.

Smith says the extra cost between single and double glazing can be between 50 and 100 per cent, depending on the company and the product. Householders can spend from a few thousand, to tens of thousands of dollars extra. “There’s a huge variance. The best bet is to shop around – there are good deals and really good products out there.”

Glazing

Glass is no longer just plain old glass. It now comes in a dazzling range of coatings and tints that will help keep your energy bills down.

Low emissivity (low-e) glass has a transparent metallic coating that reduces the pane’s U-value. “Low-e glass can significantly reduce the amount of heat that travels through your windows, keeping your house more comfortable in both summer and winter,” says Jamie Rice, vice-president of the Australian Glass and Glazing Association. It can also curtail UV light and reduce fading in furnishings.

Single-glazed low-e coated glass is a good option for people who want a step up from standard glass but can’t stretch their budgets to double glazing. However, it’s far more effective when placed inside an IGU – it can reduce the U-value of a double glazed window by half again.

Tinted glass cuts the heat transmitted into the home from direct sunlight. Available in a range of colours, tints are especially suited to west-facing windows that receive direct, summer afternoon sun. “The problem with standard tints has been that to improve the performance you end up cutting out light,” says Rice. “But there’s now a more sophisticated product, called spectrally selective tinted glass, which significantly increases solar control and only slightly decreases light transmission.”

Low-e coatings and tints can be used in combination. Together, they reduce both the U-value and the SHGC, making for a window that’s ideal for keeping out the heat.

Frames

Most window frames in Australia are made from aluminium. They’re cheap and versatile, but conduct heat very easily, which means they slice the insulating performance by up to 30 per cent. Thermally broken aluminium or composite frames offer better insulation, but they’re much more costly and, for the time being, not widely available.

Timber frames also have significantly lower U-values than aluminium. Edith Paarhammer, from Victorian window manufacturer Paarhammer, argues that although timber is more expensive, it performs better than any other framing material.

She recommends that eco-conscious buyers choose products made from either plantation timber or Forest Stewardship Council certified timber. “It’s also very important that the frames are substantial, not flimsy,” she says. “And make sure they have seals all around, so there are no draughts.”

Another high performing frame is uPVC. Only recently introduced into this country, it has a comparable thermal performance to timber, but is cheaper. Warren Miles from Ecovue says a double glazed uPVC window can cost just 25 per cent more than equivalent single glazed aluminium.

Miles says it’s crucial that buyers look for frames that minimise air leakage. “You need a complete seal between the window and the frame, and also between the frame and the structure of the building. If you can’t achieve that you may as well not worry so much about the glazing.”

Miles says it’s crucial that buyers look for frames that accommodate double glazing while also minimising air leakage. “You need a complete seal between the window and the frame, and also between the frame and the structure of the building. Reducing air infiltration is a significant part of energy efficiency.”

Few businesses are specialist window installers, although some manufacturers can also do the job. You can find them listed on the Australian Window Association website.

Retrofitting

If you’re in an existing house and want to improve your windows, you have several options. The most effective and expensive way is to remove and replace the entire window units. In some systems you can replace the glass alone.

It’s also possible to retrofit double glazing, either with glass secondary window systems or cheaper acrylic panes that attach to your window frame using magnets. Cheaper still (but less effective) is Clear Comfort, a membrane that you tape to the window frame and make taut by shrinking with a hairdryer (a 10-metre kit costs only $180).

Films are an efficient way to cut solar heat gain on existing windows. They range from almost transparent to dark grey and cost between $60 and $100 per square metre, installed. They also come with low-e coatings.

Glossary of terms

U-value: the measure of a window’s heat conduction. High insulating windows have U-values from about 3.5 down to 1.4 (the lower the better).

SHGC: Solar Heat Gain Coefficient. The measure of the heat transmitted through the window when the sun strikes it directly; 0.8 is high, 0.2 is very low.

IGU: Insulating Glazing Unit. Double or triple glazed window systems, which have sealed cavities between the glass layers.

Low-e glass: glass with a low-emissivity, metallic coating that improves its insulating qualities. Some low-e coatings also reduce the SHGC.

Spectrally selective glass: glass that allows lots of light in, while cutting out unwanted UV and solar heat gain.

Read this article in Sanctuary Magazine.

See related article: Window coverings and retrofitted double-glazing