Double-glazing and Beyond

Double-glazing and Beyond


We speak to Miglas High Performance Windows about the importance of glazing windows and doors in homes

Traditionally, windows and doors are the weakest part of a building envelope in regard to noise and thermal insulation. An estimated 49 per cent of a building’s heat loss is through its windows and doors while 87 per cent of its solar gain is through windows and doors. To achieve a thermally efficient, wellperforming home, it is important to have
balanced insulation throughout the house. It makes sense to start somewhere but it doesn’t make sense to concentrate on ceiling insulation when the windows or the walls remain a weak point. Insulating both the ceiling and the walls but not the windows could mean that during summer heat gained throughout the day can’t escape due to the insulation in the evening.

Don’t let your windows become the thermal wound in the building

Insulating your home with a superior window system means comfort and protection, energy savings all year round and reduced emission of greenhouse gases — a good way to reduce your carbon footprint while saving lots on energy bills. Our experience indicates that looking into double-glazing or being made aware of it by the energy rating usually brings about a lot of questions. However, after visiting a few window manufacturers, the confusion can be even greater.

What is double-glazing?
Compared to ordinary single-glazing with one piece of glass, double-glazing has two panes separated by a layer of concealed non-moving air (or an insulating gas such as Argon). Singleglazing usually means that the pane of glass has the same temperature as the exterior air. Being highly conductive, glass allows heat to travel through, meaning that inside and outside exchange temperature. One effect of this is known as convection. On cold days, the indoor air begins to lose temperature to the glass and starts moving downwards, making space for other heated air from above. This process repeats itself over and over and has two effects.

First, the indoor room climate right in front of the window is cold and has a chill about it. Second, as the air starts cooling it starts moving to the inside of the room (cold feet are the result). When heated, it rises again and the process starts again. This causes a constant draft in winter. The reverse effect in summer means that the air takes the warmth of the glass pane and allows the room to gain heat.

Double-glazing, on the other hand, separates the colder outside glass pane and the warmer inner glass pane with the insulating layer of gas (eg, air or argon), stopping convection and heat loss in winter or unwanted gain in summer.

Do I need double-glazing?
In Victoria, Tasmania and many parts of South Australia, as well as southern New South Wales and Western Australia, it is important to consider double-glazing — although, from our point of view, it’s a necessity. In areas of cold and moderate climate, it is an important contributor to thermal efficiency and living comfort, stopping convection and
unwanted heat loss or gain. The warmer the climate zone the less the penalty of inefficient glazing (eg in Queensland), but even there double-glazing can increase comfort levels significantly.

Looking at how different people approach the topic of double-glazing you will find two distinct groups. One group considers doubleglazing because their energy rating told them they need double-glazing. The other group is considering double-glazing because they understand the concept and know what it means for their living comfort.

My builder told me to use high-performance single-glazing rather than double-glazing

Traditionally, the first step taken to overcome the weakness of 3mm clear glass was to work with additional coatings or toned glass to reduce heat gain or loss. In regard to radiant heat that is transferred through glass, these reflective coatings might help a little, but loss through convection can’t be stopped.

Furthermore, it is very easy to scratch the exposed coatings while cleaning. That’s why high-performance double-glazing is the ultimate answer. It combines the advantage of
clear double-glazing with high-performance coatings. The insulating value (u-value) of these solutions (eg, low-emission glazing) can be more than half of coated single-glazing — and the lower the u-value, the better. This shows that high-performance single-glazing is not really high performance.

My house energy rating shows u-value and SHGC. Do I have to use these to choose windows and doors?

Value (u-value) and Solar Heat Gain Coefficient (SHGC) are minimum requirements for the insulation of frame material and glazing. You should ask your manufacturer to show you the appropriate NFRC-100 ratings that are use to show u-value and SHGC. Both values are designed to help you choose the right window system and the right glazing, but the optimal performance is not just defined by the rating — it is far more than that and it’s quite risky to just look at the energy rating.

A sensibly selected solution considers further improvements and separate suggestions for each elevation. Optimal thermal performance is not necessarily defined by maximum and minimum values, meaning every project has its own perfect configuration and has to be assessed individually to maximise advantages.

Air Infiltration (AI), or air leakage, is one of these additional values to look at. Apparently it is not part of the mandatory values, even though values above 1.0 l/m2/s could mean a significant loss or gain of heat as well as a noise problem. Furthermore, framing material hardware, seals (gaskets) and quality of craftsmanship can make a significant difference over the lifetime of a product. Only by considering all these aspects will you be able to make an informed decision about the right window system for you. Knowing the different impact of the components and the value of each will help you to make the prices comparable beyond the figure.

Will double-glazingbecome mandatory?
Looking at the latest developments and the current highest level of energy efficiency in Canberra, we expect double-glazing to become necessary in heating climates and
eventually beyond. It is planned to introduce an energy-efficiency card for every home with defined minimum standards. This means that every new home will probably have to meet six-star energy efficiency and is purely looking at the building envelope so won’t allow the energy rating to be pushed over the line simply with a bigger rainwater tank.

This means the insulation, especially with good windows, will become a very important factor. The regulations are expected to extend even to existing homes. Homeowners who want to renovate or extend will have to meet the criteria, maybe even beyond the extension for the whole house. Furthermore, it will only be possible to sell a home when the six-star energy card specifications are fulfilled. These developments will have a significant impact on the housing market and mean that you should consider the upcoming regulations today if you don’t want to face a complicated retrofit of insulation and thermal-efficient windows in the next few years. Now more than ever the saying “Do it once do it right” becomes vital. Thermal-efficient windows will add to your comfort from the day of installation and will increase the value of your property.

What other aspects of windows and doors are important to consider to ensure energy efficiency?
While looking at different double-glazing options, ask questions about what differentiates the manufacturers. This is where framing, seals and hardware become vital,
especially when evaluating the advantages of certain systems over time.

Cheap hardware means loss of airtightness over time, less ease of operation and lack of security. Foam or brushed seals cause air infiltration, contributing to unwanted heat loss or gain, and cause most noise problems. This is why Miglas uses hardware that guarantees consistent performance and secure locking over time. Multi-point locking ensures security along the perimeter of a door or opening window and contributes to the ideal compression for seals.

Miglas seals are made from Thermoplastic Elastomer (TPE), which allows the window to seal tight all year round and beyond the first few years. Miglas AliClad is a high-performance, precision-made timber window that is clad with aluminium on all outside surfaces. It combines the beauty and energy efficiency of kiln-dried, sustainable Australian hardwood, the structural abilities associated with timber and the durable external powdercoated aluminium that offers low-maintenance surface for a long life. The AliClad window and door frame maintains a u-value similar to a timber window. Various highperformance double-glazing options will offer even greater benefits and help you to achieve up to eight Window Energy Rating stars (WERS) that contribute to an outstanding House Energy Rating.

Tel: 03 9728 3999
Fax: 03 9728 3555
Photography: Andrew Lecky