Large windows are a great way to let natural light into your home and connect your interior living areas with the outdoors. Unfortunately, plain glass windows are also a major source of heat in summer and heating loss in winter. There have been some huge evolutions in energy efficient window options in recent years, to help combat this issue, without compromising on the style of your home.
People building a new home are increasingly aware and savvy when it comes to options to achieve maximum energy efficiency in their new build. This awareness comes from a growing trend in the conscious buyer completing their own research into options available for any of the following:
- Achieve higher energy star ratings;
- Meeting increasing requirements from local approval authorities;
- Decrease reliance on costly and energy-consuming items in the home;
- Improve comfort all year around, whether from the heat in summer, cold in winter or nearby noise sources.
Window Glazing is one of the best options to improve the energy efficiency in your home. However, there are a myriad of similar, competing products on the market today. For a lot of first time home buyers, it can be confusing when trying to compare these options, and weighing up the short and long terms costs, associated with each option.
We have put together this article, to help provide an accurate comparison of the most common window glaze options available today. This article was developed in conjunction with an independent, Perth new home builder, to provide real and accurate information on the options available. Please feel free to contact us to get more detailed information on the source of information and products used in this comparison.
The options we will review are:
- Clear Double glazing with low-e coating
- Clear Double glazing
- Clear Single Pane Low E glass (internal low-e coating)
- Clear Low E/ Insulating Window Film applied to standard glass
- Tinted Low E/ Insulating Window Film applied to standard glass
- Standard, single pane clear glazing
Firstly, some basic terms explained:
Also known as IGU (insulated glass units) or DGU (double glazed units), consists of 2 glass panels, separated by an air or gas filled space to reduce heat and noise transfer through the window.
There is a wide variety of double glazing available, depending on:
- thicknesses of the panels of glass;
- width of the space between the panels;
- whether the space is air filled or gas filled and;
- whether the glass used is clear glass, tinted glass, or potentially low-e glass.
Double glazed units can also be made with float glass, laminated glass or toughened glass. All these variables contribute to a large variation in the costs of double glazing.
Low E Glazing
Low E Glazing stands for “low emissivity”, where emissivity refers to the thermal energy that glass naturally emits. Glass with low-e properties is designed to release less heat energy. Glass is a natural insulator and a good absorber of heat. This heat is then gradually released into the space around the glass. This released heat energy can become unwanted heat gain in summer, or undesirable heat loss in winter.
Low-e coatings are designed to reduce this unwanted emission of heat energy. Any form of glazing can be made low-e – whether it is double glazing, float glass, laminated glass or toughened glass. Low E glass is created when the low-e coating is manufactured onto the base glass. Anecdotally, there have been reports that the low-e coating can cause a somewhat hazy appearance to glass, as well as a slightly rougher feel to the glass. It is also quite vulnerable to scratching and extra care must be taken during cleaning to avoid scratching.
U Value refers to how well a material acts as an insulator. The lower the U value, the better it performs as an insulator.
Solar Heat Gain Coefficient
SHGC or Solar Heat Gain Coefficient is a measure of how much heat is gained through your windows from the sun. The lower the number, the better it performs at rejecting heat.
The below info-graphic provides a summary comparison of these 6 products.
The Star Ratings provided relate to performance, with higher number of stars indicating a stronger performance.
The $ ratings relate to cost, where a higher number of $$ indicate a higher cost. Please refer to the case studies later in this article for examples in more detail.
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While the above info-graphic is simplified, let’s look more closely at the U-value and SHGC figures for each option.
The U Value (where remember, a lower value is better) for double glazing varies from 1.91 (for double glazing combined with a low-e surface) to 2.72 (clear double glazing), which means that double glazing remains the gold standard for winter insulating performance. The single pane low e glass and insulating window film options both achieve a U Value of a respectable 3.63,4, while standard glass without any film or low-e coating has a U value of 5.85.
The SHGC (again, where a lower value is better) is where the Insulated Window Film outperforms its rivals. 3M’s tinted Thinsulate CC40 achieves a SHGC of 0.404 when applied to clear glass, while the clear Thinsulate CC75 achieves a SHGC of 0.534. By contrast, single pane clear low-e glass achieves a SHGC of 0.683, and double glazing achieves between 0.601 (for low-e double glazing) and 0.722 (for clear double glazing). Standard clear glazing has a SHGC of 0.825. These results show that the 3M Thinsulate low-e window film will perform much more strongly during Perth summers to reject both solar and infra-red heat sources to keep you more comfortable and reduce dependence on air conditioning.
- Specification for Viridian Comfort Plus Clear 82 IGU;
- Specification for Viridian VFloat Clear IGU;
- Specification for Viridian Comfort Plus 82 on 6.38 clear;
- 3M Thinsulate Climate Control Specification
- Viridian Performance Data V-Float Clear 6mm
These case studies were drawn from actual house plans of new builds completed in the Perth area. Each house was calculated for 3 different glass upgrade options:
- Low-e Window film applied to standard glass option included in new home build costing
- Upgrade of standard glass to low-e “Comfort Plus” glass and
- Upgrade of standard glass to double glazing and associated framing/ hardware to accommodate double glazing.
The results are tabulated below. The figures given for square metres of the home is the total square metres of living space within the home, excluding garages, alfrescos and balconies.
In the above-mentioned case studies, reviewing 4 different homes of differing sizes and glass quantities, the low-e window film was consistently a more cost-effective option over the low-e glazing or double-glazing upgrades.
Low E Glazing upgrade was between 5% – 21% more expensive than the low-e window film option. Double glazing was consistently around 300% more expensive than the low-e window film option.
3M Thinsulate Low-E Window Film
Relatively new to the market, the affordability of 3M Thinsulate low-e window film compared to other glazing upgrade options, coupled with the lifetime warranty and a much stronger heat rejection performance in summer, makes it an excellent option for home buyers wanting to improve their energy efficiency without breaking the bank during their new home build.
While double glazing remains the “gold standard” for features of heat retention in winter and noise reduction, the cost of this option is prohibitive for many. The slightly lower performance of low-e glazing and low-e window film during winter, is arguably not a major issue in the Perth climate, where the weather is more temperate compared to other parts of Australia that experience harsher winter weather.
The stronger performance in hot weather of the low-e window film from 3M is likely to appeal to many buyers for surviving Perth summers. Future maintenance costs are also likely to be more favourable for the Low-E Window Film, with this option being the only option to offer a lifetime manufacturer’s warranty. If the film is damaged via accidental damage (not covered by warranty), then the cost of removing and replacing a piece of damaged film is a much more cost efficient option than replacing a whole panel of low-e coated glass or an entire double glazed unit.
For more information on your energy efficient window options, speak to one of our experts at Complete Film Solutions, to make sure you choose the right options for your new home.