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85% of Windows going into Australian Homes are Single Glazed in 2017?

As a homeowner, Architect, Builder or Engineer, if you are located on the continent of Australia, you are likely to have encountered the question:

Single or double glazing, which is best for my home or project?

For many who have a grounding in fundamental physics (or logic), this is a question that was answered a long time ago when considering the energy efficiency benefits of double glazed over single glazed. Simply put, how can a glass product first developed in the early 1950's still be the default glass option for so much of our industry with 85% of market share? But for many others, this remains a question clouded by contradicting guidance and industry direction.

Today, in January 2017, this question may very well be a weekly occurrence in the Australian construction industry. The nearer you get to the equator, the more often it will come up! In a post-truth world, will this debate grounded in little more than hearsay or local narratives appealing to emotion and personal belief continue to gain traction? Or will some good old fashioned logic lead us down a clearer path to more comfortable, energy efficient homes and chip away at some of the 85% market share currently enjoyed by the single glazing component of the window industry.

To be honest, Scooby Doo and The Mystery Machine are not needed to uncover why so much debate still exists, as the supernatural perpetrators would quickly reveal themselves to be those with vested interests, often hyper-sensitive to change and risk of adding additional costs to projects. Not driven by the quality of the end product, energy efficiency or comfort and health of occupants, but by a short-term goal of securing a contract and moving onto the next.

Indeed, even a very well-known industry body jumped into this single glazing debate last year. Published in The Age late last year (Saturday November 12th, 2016), Kristen Brookfield (Senior Executive Director of Building, Development and the Environment of the Housing Industry Association - HIA) was quoted as saying:

 ‘... Double glazing is slowly giving way to low-emission, high-performance single-glazed design. …the product can provide the same performance of double-glazed windows… link’ 

Addressing the above in a bit more detail, this statement eludes to a mythical product called ‘low-emission, high-performance single-glazed design’ meeting the performance of double-glazed windows. This is equally alarming as it is misleading.

In a world where all is seemingly relative, are we being lead to believe a lower performing semi-insulating single glazed product (with a low-e coating) has the ability to equal the insulating performance of a double glazed unit? Is this our default industry position unless proved otherwise?

While I feel the extract above and article it was taken from was perhaps at risk of misquoting the HIA, I do believe there are good reasons for some of our construction industry to take a default position of single over double-glazing that go beyond the obvious position of cheaper construction materials, logistics for contractors and the inherent bias of the single glazing salesman or sub-contractor. 

Not to point the finger in any one particular direction, as this is not a simple issue and is fundamentally cultural as it is logical. But perhaps a simple reason why our industry continues to push for single over double glazing in Class 1 (Single Dwellings) at least is seemingly illustrated by the default position of the Australian Federal Government!

On YourHome - Australian Guide to Environmentally Sustainable Homes, you are given the ingredients in all Australian climate zones to achieve a 7 Star NatHERS Rating (a flawed process and not the subject of this article) through base specifications for floors, ceilings, roof, external and internal walls, draught sealing and glazing.

Dig a little deeper and you find low quality, single glazing combined with poor quality framing are the default position for even Hobart to achieve these magical 7 Star NatHERS rated designs. This is seemingly at odds with glazing advice on the same website where it is stated 'Windows can severely impact on the heating and cooling loads of a building'. Such disjointed, mixed messages are confusing at the least but very reflective of the ongoing, risk adverse position to avoid any ‘cost increases’ to construction.

And while deeply misleading in terms of the virtues of ‘Environmentally Sustainable Homes’, given that the YourHome NatHERS advice completely omits build quality, occupant comfort, safety, condensation risk, mould growth and acoustic attenuation, all inherent features of a standard double glazed unit to vary degrees, taking this advice could be very risky indeed!

Happily, while YourHome is seemingly devoid of ambition or confusing at the least, the NSW Department of Planning & Environment are stepping up and have recently announced increases to the BASIX energy targets as of July 2017 - houses and low-rise units increase by 10% and high-rise units to increase by 5%. The increases recognise the importance of energy efficiency and particularly the performance of glazing and its role on comfort in both decreasing energy use and costs to consumers.

So for those homeowners, Architects, Builders or Engineers considering single or double glazing and which is best for your project, please do not let your decision be determined by energy efficiency virtues narrated through the broken NatHERS rating system or you may very well be deeply disappointed with the results. Consider occupant comfort first, and energy efficiency will follow!


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