Michael Green

Writer and producer

Thermal mass

In Greener Homes on

Well-placed, high-density materials can keep your home comfortable.

By and large, when house designers mention “thermal mass“, their clients’ minds go blank. The topic seems as impenetrable as a thick bluestone wall.

Sustainable building expert Dr Chris Reardon, of Suntech Design, says it’s a crucial concept for people to grasp – and it’s actually not so complex. “Thermal mass is the battery of passive heating and cooling,” he explains. “It’s where you store free heat from the sun, or free cooling from breezes or radiation to clear night skies.”

Dense building materials, such as concrete, brick, earth or tiles, have high thermal mass – they need a lot of heat energy to warm them up and they retain the heat for a long time. “The main value of thermal mass is to even out day/night temperature ranges. In winter, it stores daytime solar heat and augments night temperatures. In summer, stored night ‘coolth’ can absorb daytime heat gains,” Dr Reardon says. In contrast, lightweight materials heat and cool rapidly.

High-density materials are helpful in climates where there’s a gap of more than six degrees between daytime maximums and night-time minimums. In Melbourne, the temperature often varies by 10 degrees or more. “The more extreme the climate, the more thermal mass you need,” he says.

But mass is just one element of good solar passive design. If not co-ordinated with the orientation, windows, shading and insulation, the heavy materials can accentuate the worst aspects of the climate – the home could absorb extra warmth in summer and stay colder in winter.

“Thermal mass must be exposed on the inside of the house and insulated from the outside,” Dr Reardon explains. For example, the timber and plasterboard internal wall in a brick veneer home insulates the mass in the bricks, meaning they don’t help to curb temperature extremes. The mass is better put to use in reverse brick veneer construction, or by designing internal feature walls of exposed brick, cement-rendered brick or earth.

According to Riccardo Zen, from Zen Architects in North Fitzroy, carefully placed high-density materials are essential to cut energy needs for homes in Victoria. “Our basic goal is to eliminate heating and cooling in our buildings,” he says. “It’s very hard to do that unless you have some form of mass.”

A classic example of thermal mass is an exposed concrete slab floor, positioned in front of windows in a north-facing living room. In the winter, the sun can shine directly on the slab, which absorbs the radiation and warms the house into the night.  With appropriate shading, sunlight won’t hit the concrete in summer and the chill of the slab will help the home stay cool.

You don’t have to start from scratch to improve the thermal mass in your home. Mr Zen says building designers are learning nifty ways to add high-density materials to existing houses, including suspended slabs, aerated concrete blocks and tiles. “We did a project where we brought concrete pavers onto a timber floor using the existing joists,” he says.

“People are also experimenting with using water tanks. Water is one of the best forms of thermal mass – you can also shift it and put it back seasonally when it’s required,” Mr Zen says. “We’re becoming more sophisticated in the way we use mass. There are some hybrid systems evolving to tackle difficult sites.”

Reducing building waste

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Plan carefully so you don’t waste building materials.

Construction waste comprises up to 40 per cent of landfill in Australia, according to the building design guide, Your Home. Mark Sanders, managing director of Third Ecology, an architecture and building firm in Geelong, says that with a combination of thoughtful design, planning and site management, most waste can be avoided or salvaged. “The waste hierarchy of reduce, reuse and recycle applies to a building site, just like anything else,” he says.

There are a number of steps you can take before you begin to build or renovate. Talk to your designer first – smaller homes use less of everything, so the best way to cut the amount of materials needed for your home is to limit its size. Similarly, if you’re renovating, the thriftiest tactic is to keep as much of the existing building as you can.

The dimensions of the design will also affect rubbish on site. “Materials come in certain widths and lengths,” Mr Sanders says. “We can design with the standard sizes in mind to get the maximum use out of materials and minimise the waste.”

Using prefabricated products, such as frames and roofing, will also save landfill. “If some of the work can be done in a controlled, factory-type environment, then there should be not only less waste, but also better ways of dealing with the waste that does occur,” Mr Sanders says.

The next level in the hierarchy is reuse. Many building products are available pre-loved. Intact items such as doors are ideal for refitting. Material-wise almost everything can be reclaimed, from plasterboard, timber and glass, to metals like steel, aluminium and copper. Even concrete, plastics, bricks are good to go around again and are widely recycled by waste contractors.

But Mr Sanders offers a word of caution to over-eager scavengers. “The recycled products need to be fit for purpose. It’s not just a matter of using any old thing,” he says. “Make sure you’re aware of any issues that may mean the product is not as good as the alternative new one.”

If you’re willing to spend time, you’ll save money. It can be well worth your while fossicking for items with character. “You can come across some really beautiful timber,” Mr Sanders says. “Second hand resources are cheap to purchase, but they can need more labour to bring them up to scratch.”

To best recycle the waste produced on site, you have to get your builder onside, according to Enzo Bruscella, executive officer of the Barwon Regional Waste Management Group. “Speak to them about how they’re going to manage the site and the materials that come off it.”

To guarantee a good job, ask for a waste management plan, including targets for resource recovery and landfill waste reduction. It shouldn’t make your project more expensive, because any extra costs can be offset by lower disposal fees and the sale of salvaged resources. “These materials have value. We really don’t want them going to landfill,” Mr Bruscella says.

On the whole, the building industry has been slow to clean up its leftovers, so it’s important for householders to demand better standards. If you (or your builder) want more information, contact Keep Australian Beautiful Victoria, or your regional waste management group.

 

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

Preserving

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Save the sweet summer produce from waste.

Matthew Pember is ready to take over the family sauce-making tradition. Next weekend, his relatives and friends will bring over their tomato crop and renew their annual sugo day. “Making our own tomato sauce has been a tradition ever since I can remember,” he says. “It’s a big event.”

Together with his business partner Fabian Capomolla, Mr Pember runs The Little Veggie Patch Company, which designs and installs and organic backyard vegetable gardens. Both men come from Italian-Australian families. “It’s time for our generation to carry it on, but my Nonna and my parents will be there to lend their expertise.” They’ll convert the season’s ripe tomatoes into sauce that will last through winter, before sitting down to a traditional lunch.

The sauce is simple: boil the tomatoes, remove the skins and seeds (Mr Pember uses a small hand-operated machine), and bottle the pulp. A kilo of tomatoes makes about 750 ml of sauce. “We just add salt and a couple of basil leaves. When you cook the pasta sauce to eat, that’s when you add the oil, garlic and herbs.” The sealed bottles are boiled to stop the sauce fermenting in storage.

“If you look after your plot, this is the most exciting time of year. There’s so much fruit falling off trees – you tend to get a glut of food at the one time, so it’s important to put it to good use,” Mr Pember says.

Even if you’re not a backyard gardener, preserving the summer’s crop brings sweet rewards, according Anna Lohse. She’s the founder of Nanna Technology, a website dedicated to upholding time-honoured skills such as gardening and cooking.

“My garden isn’t well-established yet, so I go to the market and buy cheap fruit and veg in bulk,” she says. “[Recently] I bought boxes of tomatoes, plums, peaches and apricots, and went crazy.” She finished with a battery of bottled fruit, chutneys and jams.

There are many ways to keep your crops, from freezing, bottling and drying, to pickling, salting and juicing. Ms Lohse says first time preservers can’t go wrong with jam. “People think jam is hard, but it’s actually really simple and delicious – it’s basically equal quantities of sugar and fruit. Cook it together until the sugar is dissolved and it gets to a runny, jammy consistency.”

When bottling, you have to be careful with hygiene. One technique is to wash your jars and dry them in a low oven, while bringing the lids to boil in a pot of water. “The rule is to put a hot liquid into hot jars and seal with a hot lid,” she says. “There are all sorts of different ways to do it, but that one is easy and has always worked for me.”

Ms Lohse says preserving means she can eat seasonal fruit and vegetables, but not forgo the best flavours. “In winter I miss some of the produce you can get in summer, so it’s very exciting to open up a jar of peaches in the middle of winter and make a delicious pie or tart.”

She also makes her jams and chutneys for the pure pleasure of taking time over her food. “Preserving is a way for me to slow down and enjoy the produce, and also enjoy a slower life.”

Indoor air quality

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Clear air takes care, especially if you’re building.

Most people think of their homes as havens, but the air quality inside can be far worse than outside, even in a busy city.

Marianne Baker, president of the Australian Society of Building Biologists, says a number of factors diminish air quality, including dust and mould. In recent years, people have also become more aware – and wary – of products containing Volatile Organic Compounds (VOCs), chemicals containing carbon that slowly ‘offgas’ into the air.

Although few VOCs have been studied in detail, a number of health effects are known. “The symptoms vary from person to person, but can include headaches, tiredness, or irritation of eyes, nose and throat,” Ms Baker says.

Even so, they’re ubiquitous in our household products, construction materials and furnishings. Unless you take special care, VOCs will emerge from your new carpet, paint, cupboards, varnish, adhesives and synthetic fabrics, as well as from day-to-day cleaning and pest control products, air fresheners and deodorants.

Construction products offgas the most when they are new. For this reason, the decisions you make when you build or renovate are crucial, because you’re installing scores of products all at once.

Low- or no-VOC products are available, including natural paints, sealants and finishes, and natural-fibre floor coverings (such as sisal or jute). Ecospecifier, an eco-friendly product database, is a great place to research what’s on offer. “Seek advice about healthy building materials,” Ms Baker suggests, “and make sure the design allows for excellent cross-flow ventilation.”

Good ventilation is essential for good indoor air quality. “If the air is stagnant, chemicals released from the building materials will accumulate inside,” Ms Baker says.

Jo Immig is an environmental scientist and the coordinator of the National Toxics Network. She says parents should be especially wary of the products they use around the house. “Children are at far greater risk of exposure to any chemicals because their body is developing. They breathe more air per body-kilogram than adults.”

She says most of us can dramatically improve our air quality by adopting a handful of different habits, as well as by improving ventilation. “I encourage people to switch from petrochemical-based, heavily perfumed cleaning products to plant-based, low-toxic cleaning products.” Similarly, she recommends against buying plug-in or aerosol air fresheners.

And if you’ve got pest trouble, try to target the cause of the problem. “For example, with cockroaches, seal up cracks and crevices, rather than getting a pest control company to come once a year and spray the place with chemicals,” Ms Immig says.

Unflued gas heaters are also a health hazard. When gas is burnt it releases nitrogen dioxide, which contributes to chronic respiratory disease. “Any indoor gas appliance that is not properly vented is potentially a big contributor to indoor pollution,” Ms Immig says.

Her other simple suggestions include coughing up for a vacuum with high filter efficiency (HEPA filter) and removing your shoes at the door. Particles of heavy metals, such as lead, cling to the soles of our shoes – so at the least, be sure to place doormats at every entry.

Indoor plants can also help you breathe easy. “Plants have a lot to offer,” Ms Immig says, “not just their potential for cleaning the air, but for the overall feeling of wellbeing in the home.”

For more information, visit safersolutions.org.au