The first principle of keeping your home cool is keeping out the heat in the first place. This simple advice comes courtesy of NABERS, but it seems that few are listening. Warren McLaren takes a peek at nine shading products which keep the heat out.
Fillums
The Window Film Association of Australia and New Zealand (WFAANZ) tout the example of a Victorian house that managed a 30 per cent return on investment in 12 months as a result of installing a solar window film and saving on air-conditioning energy costs. One such product is Bekaert‘s Solar Gard, which claims to reflect up to 79 per cent of solar heat gain and 99 per cent of UV light. An optically clear film, Solar Gard is installed on the interior of existing windows to give a performance like that found on windows that come with a factory applied low-E (low-emissivity) finish. 3M has a similar product with its Scotchtint and Scotchshield window films. Whilst Energy Management Films offer its EnergyMF film, which it suggests can offer energy savings up to 35 per cent, given that it blocks solar heat gain by 80 per cent and glare by 85 per cent.
Slattery flattery
What is a verandah that is full of holes? A pergola. When the angle of the slatted roof of a pergola has been carefully calculated, it should ward off the peak intensity of the summer sun, yet allow those same warming rays to strike a window during the height of winter. A paragon of passive solar design, pergolas can even steal some of the deciduous tree’s thunder. Instead of slats in the roof a thin wire frame can support vines, like grapes. In the hot seasons these generate a dense, dappled shade, only to have all that foliage disappear just in time for winter. Throw technology at a pergola and you might get something like the Vergola. Although requiring a 12 volt DC motor, a Vergola’s double-skinned louvres can be adjusted to the optimum angle to impede or allow ingress on warm sunlight.
Thank you, eaves
Yes, eaves. Who’ve had thought it? Certainly not the builders and buyers of the current trend for McMansions that have dumped on eaves so they might have bigger houses by being closer to property boundaries. Yet appropriately scaled eaves might even nudge out deciduous trees as providing the most bang for buck in the shading game. They add little to the costs of construction as they are integral to a roofline, rather than an additional add-on. With the correct depth of eave for a given latitude, it is possible to shade much of a single-storey structure’s walls and windows from the high summer sun. Dedicated window eaves can be incorporated into multi-storey buildings. Wide eaves evolved over millennia of building design, based on astute observation and application of natural phenomena. The advent of air-conditioning killed off eaves, just as it did verandahs, cross ventilation and judicious siting. Eaves are clever design. Air-conditioning is just lazy.
Porch 911
Verandahs were once as Australian as swimming gold medals. The colonial farmhouse had them, often on all four walls. Bull-nosed verandahs adorn many a beloved hotel balcony or sought after terrace house. For a time, verandahs fell out of favour as part of the ‘modern’ design aesthetic. Enlightened architects have fortunately retained an appreciation of their value. For example, some years ago, the Shellharbour Workers Club (NSW) installed a $3 million verandah, complete with integrated photovoltaic system that annually generates about 25,000 kWh of electricity. The additional 1,500 sqm of space doesn’t need air-conditioning, saving an estimated 370 tonnes in greenhouse gas emissions. A life cycle analysis of verandahs in the NT found their expense and embodied energy likely to exceed that of evaporative air coolers or wall insulation alternatives, but did concede this equation changed when refrigerative air-conditioners were considered. And a verandah’s higher cost also greatly extends a building’s living space.
Autumn manoeuvres
Possibly the most cost-effective option for screening windows and walls from solar heat gain is to plant deciduous trees to the north of the building. A classic passive design tool, the dense foliage of the trees provides much welcome shade relief during the summer months. Yet leaves fall off during autumn, allowing the bare tree to permit low angled winter sun to penetrate windows and passively warm otherwise cold buildings. Unfortunately, Australia only sports a half dozen native deciduous trees, (Illawarra Flame, Silky Oak Tree, Australian Red Cedar, White Cedar, Deciduous Tanglefoot Beech and the Boab Tree), none of which, alas, are really suitable for this application. The next best green option is to opt for food-bearing deciduous fruit or nut trees. After this there are umpteen classics, such oaks and maples. One US energy utility is so convinced that trees can cut home cooling costs by up to 40 per cent that it provided customers with free shade trees. Just having a tree shade an air-conditioner’s external box can save 10 per cent in air-conditioning costs.
Shutter with delight
Awnings aren’t the only shading devices being made over. Shutters are in on the act too. Although often termed ‘plantation shutters’ as a reference to their use on grand estates in the American south, their real functional heritage can be traced to the streets of ancient European city apartments. A worthy companion to the classic French window, shutters, with their small rotating timber louvres, not only render a room privacy, but also protection from the sun. They also allow for cooling breezes to enter. Open Shutters has 20 years experience making window shutters for the Australian climate and market. Tests it has gathered suggest its shutters exhibit a 47 per cent reduction in heat transfer. Partly this is due to a snug, custom fit which traps an insulation layer of air between the shutter and window, and partly because it believes 1 cm of its Western Red Cedar equates to 4 cm of brick.
Come sail with me
If verandahs have not received the recognition they’re due, maybe it’s because shade sails have, of late, been stealing much of the limelight. Shade sails block up to 90 per cent of UV light from reaching a window or wall. One of the more known exponents of this shading treatment is Coolaroo, whose polyethylene is knitted instead of woven, a construction it feels increases the fabric’s resistance to tearing or fraying. The open knit allows for air to pass through the sail, providing what it terms a ‘breathing effect’. This, it suggests, reduces temperatures beneath the shades by up to 32 per cent, relative to direct sunlight. Shade cloth sails can be fitted retrospectively and cost competitively to older structures that might not otherwise suit a verandah upgrade. If thoughtfully installed, shade sails have the ability to be removed during winter to allow warming winter sun to enter buildings.
Blinded to the light
Blinds, like curtains, rarely get most people excited. Built environment magazines are more likely to show acres of glass with panoramic views than to focus on blinds. But then air-conditioning’s enormous energy bills aren’t very attractive either. Helioscreen make blinds that may cause designers to rethink their prejudices towards blinds. In one case study its external Heliogreen blinds were estimated to halve energy use in Australia’s first environmentally sustainable strata office project on Sydney’s northern beaches. While we’d prefer they found something other than PVC with which to coat such blinds (as the Vertilux collection does), such energy saving claims are impressive. Admittedly, it’s far better to shade the outside of windows, keeping the heat outside the building shell, but there may be buildings where this is problematic. In these instances, internal blinds could well be a last line of defence against the excessive heat flow in to a room.
