he relative merits of both timber and aluminium are at the heart of the window energy efficiency issue, and so these considerations need to be addressed in order to make an effective choice when installing new windows and doors. Tracy Gramlick, technical director from the Australian WindowAssociation, says important factors to bear in mind include aesthetics, cost, the provision of daylight, glare control, thermal comfort and ventilation. “Certain practical considerations such as resistance to condensation, sound control, maintenance requirements, durability, compliance with structural code and water tightness should also influence the decision making process,” she says.
There are various pros and cons to both timber and aluminium. With timber, the most obvious one is the warmth that it displays in its touch and feel. With an aesthetically pleasing grain, especially when it is stained rather than painted, timber can also be energy efficient as it can be an excellent natural thermal dampener.
There are also pros for aluminium. A recent study undertaken by Branz found that aluminium-skinned timber framed windows out-performed other window types when tested for energy efficiency. David Richardson of TrendWindows & Doors, which supplies both materials, says aluminium is low maintenance and can be powder-coated to many colours to highlight the feature of the windows and/or doors. “Aluminium is certainly structurally stronger, especially in high wind areas too,” he says.
With aluminium used in around 74 per cent of residential applications (and timber making up about 24 per cent) and 99 per cent for commercial, the cost of aluminium is low compared to timber so it is much more widely used for this reason. Aluminium can also be made into many shapes and therefore can be made into very large window and door combinations due to the strength of the product. “Both are long lasting if installed and maintained correctly. However, timber requires higher maintenance. If it is not maintained, then the life is reduced dramatically, depending on the type of timber,” says Richardson.
The main disadvantage of timber is the need for maintenance, especially when it is stained or exposed to weathering or the sun. “It can be bruised and damaged by a number of attacks and once it is, then the damage is difficult to repair,” Richardson says. “Timber in long lengths is also subject to movement such as warping and twisting in the material, so large panels are not recommended.”
Timber and aluminium are used in most applications around Australia, from the very hottest to the very coldest climates. However, where strength is required, Steve Olley, technical services manager at Wintec Aluminium, says aluminium is always specified. “Aluminium windows and doors are capable of withstanding extremes of weather with the correct use of extrusion shape and mass, whilst also being able to maintain clean lines and soft curves,” he says. “The flexibility of design with extended aluminium allows for windows and doors to be used in any type of building, from basic sliding products in cheap affordable housing through to monumental buildings.”
Although aluminium is 100 per cent recyclable, it can be a poor insulator due to its high thermal conductivity. As a result, a large proportion of energy due to heating or cooling can be lost through the frame. This problem is currently being addressed by window manufacturers now that energy efficiency is being legislated and energy targets are becoming more stringent. While thermally broken aluminium is available, Olley says it is very expensive.
In many of Australia’s coastal areas, timber is often more specifically chosen for its aesthetic appeal rather than for its serviceability, Richardson says. “Aluminium, meanwhile, is like any painted product. If it is maintained like your car in similar environments, the weathering qualities of the surface will last the life of your building. More durable paint finishes can be used, but again maintenance is important. In high spray areas, such as surf coasts, then the upkeep is more crucial. But as long as the salt is removed, then the surface will be long lasting.”
Timber is widely used in bush and mountain areas for a more natural look in keeping with the local environment. The exception is in areas of high-risk, bush-fire zones where aluminium is more resilient. Andrew Moar, owner of Moar Windows and Doors, says price will always be a factor with timber, which is often up to 50 per cent more expensive than aluminium. This is contrary to some opinions in the industry which states that differences often depend on the individual products.
Moar says that to quote a certain figure between the two is not easy, as the difference of each product must be taken into account based on the relative features and benefits of each. “In some cases, the cost of an aluminium product of the same type and size as timber may in fact be around the same cost due to the material and labour to make the joinery,” says Richardson. Also, different timbers will vary in price, and availability will have an influence too, Richardson says.
Environmental friendliness is a hot topic in the discussion between the two materials. The debate about the embodied energy in the manufacture of aluminium is a concern, but the ability to recycle the product at 5 per cent of the initial energy consumption means that it does not use anywhere near the amount of energy as the initial use. Timber, on the other hand, says Richardson, not only involves cutting down native forests, “but also uses [a lot of] energy in the cutting, transporting, re-working, transporting again, manufacturing and transporting again that occurs”.
On the Moar Windows and Doors website, it says aluminium production results in eight times the air emissions and 300 times the water emissions of lumber production. And with its slogan of, “Choose wisely, choose wood,” Moar says wood is the only readily renewable natural resource which is increasing in reserves every year.
Early life cycle analyses undertaken regarding environmental friendliness have the three most common frame materials (the other one is uPVC, which is only being more recently developed in Australia) coming out about even over a 50-year period. However, much more work needs to be done in this area before more qualified responses can be provided.