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Secondary Glazing vs Double Glazing: What’s the Difference?

Secondary Glazing vs Double Glazing

Secondary Glazing vs Double Glazing: What’s the Difference?

Posted on in Blog

When you’re looking to improve soundproofing and energy efficiency in your home, choosing between secondary glazing and double glazing can be a tough call. Both options have their perks, but they have different features that might affect your requirement. Understanding the key differences between the two is essential for making the right decision that fits your home, budget, and specific requirements.

Whether you’re after affordability, ease of installation, or maximum performance, knowing what each option offers will help you pick the right solution for your situation.

 

Secondary Window Glazing

Secondary window glazing involves adding another set of window to the inside of your existing window reveal. It’s a non-intrusive solution that doesn’t require replacing your original windows, making it an ideal choice for homeowners, especially those with heritage or period properties where keeping the original look is important.

No Structural Changes, Minimal Aesthetic Impact

One of the most significant advantages of secondary window glazing is that it requires no structural changes to your existing windows. The secondary window is installed within the existing window reveal, meaning the overall aesthetic of your home remains largely unchanged. This is particularly important for homeowners with older properties, where the windows often contribute to the character and charm of the building.

Because secondary glazing is installed on the interior side of the window, it’s practically invisible from the outside. This allows homeowners to retain the external appearance of their property, which is especially crucial in areas where strict planning regulations apply, such as in conservation areas or with heritage-listed buildings.

A Cost-Effective Solution

Cost is often a determining factor when upgrading windows, and secondary window or door glazing is generally a more affordable option compared to double glazing. This is because it involves less material and labour. There’s no need to remove and replace the existing windows, which not only reduces the cost but also minimises disruption to your home during installation.

For homeowners looking to improve energy efficiency and reduce noise pollution on a budget, secondary glazing is a smart, practical choice. You get a lot of the benefits of secondary window glazing, but at a lower price.

Tailored Air Cavity for Specific Needs

Another great thing about secondary window glazing is that you can customise the air cavity between the original window and the secondary window. This gap can be adjusted to meet specific needs, whether you’re looking for an optimum soundproofing, improved thermal insulation or a mix of both.

For example, if you live near a busy road or in a noisy area, a larger air gap can help block out more noise, making your home quieter and more peaceful. But if temperature is your main concern, a narrower air gap is sufficient for thermal insulation without affecting the appearance of your windows.

Double Glazed Windows

Double glazing, however, means installing a brand-new window unit that features two panes of glass separated by a narrow gap, often filled with an inert gas like argon. This option is typically favoured for new constructions or when old windows need replacing because they’re damaged or not performing well.

Replacing Existing Windows, Potential Aesthetic Changes

Unlike secondary window glazing, double glazing involves removing your old windows and replacing them with entirely new units. This process will likely change the appearance of your home, especially when viewed from the outside. Although modern double-glazing designs aim to be as subtle as possible, you might still notice a difference in how your windows look.

This could be something to think about if you’re keen on preserving the original charm of your home, particularly with older properties. But if you have a newer home or are more focused on improving performance than maintaining a specific aesthetic, double glazing could be the way to go.

Higher Cost Due to Comprehensive Installation 

Installing double glazed window is a bit more involved than secondary glazing, and that’s reflected in the cost. Since it requires replacing the entire window unit, including the frame, the cost can be more expensive. However, some may see this as an investment that typically pays off over time. Double glazing can enhance your home’s energy efficiency, helping to cut down on heating and cooling bills.

When comes to selling your home, double glazing also often perceived as a valuable upgrade. Buyers usually appreciate the added comfort and efficiency it brings, which can make your property more appealing on the market.

Standardised Air Cavity

The traditional double glazing is usually comes with a narrow gap between the two panes of glass. This setup allows them to have less bulky frame to fit most situations. It however may not give you the optimum soundproofing that you required. Plus, if you opt for a wider gap, it might change the appearance of your windows, which could be a factor if you’re keen on preserving a specific look.

Both secondary windows glazing and double-glazed windows offer distinct benefits, and the choice between them should be guided by your specific needs, budget, and the characteristics of your home. Secondary windows glazing stands out as a cost-effective, minimally intrusive option that allows you to retain the original windows and aesthetic of your property, with the added benefit of customisable air cavities for specific insulation or soundproofing needs. Double glazing provides a comprehensive solution for new build homes, delivering an improved energy efficiency and noise reduction, with the potential to add value to your home.

Ultimately, the right choice comes down to what matters most to you—whether it’s keeping your home’s current look, staying within budget, or getting the best insulation and soundproofing. By understanding the differences between these options, you’ll be able to make a decision that fits your needs perfectly.

For expert guidance on the best choice for your home, speak to Magnetite team today.

  1. Conduction
    Heat moving through an object (i.e. heat will travel through an aluminium, or steel frame more easily than through a timber or PVC frame).
  2. Radiant heat
    Heat from the direct sun. It can pass through space until reflected or absorbed.
  3. Convection
    Heat flow resulting from air movement e.g. either 'natural' convection - warm air rises, or 'forced' convection - a breeze by a window, both can result in a draught by a window.
  4. Infiltration
    Air leaks around the frame, around the window sash and through the gaps in the movable window parts.

When evaluating your options to improve the thermal performance of your windows, the following double glazing key performance criteria should be considered:

  • U-Value (Uw) represents heat transfer through a window, irrespective of direct sunlight. The lower a window’s U-Value, the better the insulation performance.
  • Solar Heat Gain Coefficient (SHGC) measures the solar energy that passes through glazing. The lower the SHGC, the less solar heat is transmitted through a window.
  • Air Infiltration or leakage measures the rate at which air passes through gaps in window joins and seals. The lower the air infiltration, the better a window’s energy performance.

The Window Energy Rating Scheme (WERS) Thermal Performance

Aluminium Frame Windows

Glazing Type Cooling Stars Heating Stars Cool% Heat% Uw SHGC
Single glazed 3mm clear glass* half blue star red starhalf red star 7.4 0.77
Single glazed 3mm clear glass &
4.5mm Magnetite		 blue starblue starhalf blue star red starred starred starred starred starhalf red star 35% 59% 2.9 0.67

Timber Frame Windows

Glazing Type Cooling Stars Heating Stars Cool% Heat% Uw SHGC
Single glazed 3mm clear glass* blue starhalf blue star red starred starred starhalf red star 20% 28% 5.5 0.69
Single glazed 3mm clear glass &
4.5mm Magnetite		 blue starblue starhalf blue star red starred starred starred starred starred star 37% 61% 2.6 0.66
Single glazed 3mm clear glass with
Solartite** and 4.5mm Magnetite		 blue starblue starblue starblue starblue starblue starhalf blue star red starred starred starred starhalf red star 76% 45% 1.8 0.20

 

*WERS standard typical industry window
**Solartite is a range of high performance window film. The window tested above has Solartite’s low-e film.

Magnetite vs Traditional Double Glazing – What the experts says

Winter - the ideal situation is to let in as much of the sun's heat and then trap it inside to maintain a comfortable environment in your home or office. This will also significantly reduce heating costs and saves you money. The ideal window for winter will have a high SHGC to let the sun's heat in and a low U-Value to prevent the heat from escaping. Clear windows without shading films are better suited for winter climates.

Compared with traditional double-glazing, Magnetite’s double-glazing solution can provide better results during winter or for cold climate areas such as Canberra, the Adelaide Hills and Blue Mountains.

Magnetite's clear acrylic window panels allow the direct heat from the sun's rays to enter the building and once inside, Magnetite's superior magnetic seals retain the heat, giving Magnetite an advantage over conventional operating windows.

Glazing Type Cooling Stars Heating Stars Cool% Heat% Uw SHGC AI
Double Glazed 3mm clear glass/12mm air
gap/3mm clear glass IGU (Insulated Glass Unit)*		 blue starblue starhalf blue star red starred starred starred starred starhalf red star 40% 55% 3.0 0.61 5.0
Single glazed 3mm clear glass &
4.5mm Magnetite		 blue starblue starhalf blue star red starred starred starred starred starred star 37% 61% 2.6 0.66 0.5

 

*WERS standard typical industry window

Summer - the ideal situation is to minimize the heat coming in from outside and prevent the cool air inside from escaping through the window. This will make your home more comfortable and reduce your air-conditioning costs. The ideal window for summer, or for a large west-facing window, will have a low SHGC to limit the heat from the sun's direct rays, as well as, a low U-Value to prevent the heat in the air outside from moving through the window and warming the cool conditioned air inside. It is better to have a shading film on the first (outer) glass pane to limit the heat that enters the double glazed unit.

The combination of Magnetite retrofit double glazing and Solartite outperforms the traditional insulated glass unit for hot climate. Magnetite fit over an existing window with reflective film will give better summer heat control than a double-glazed window with supertoned glass.

The Magnetite system stops the conduction and convection of heat better than glass windows giving superior results for summer conditions. Combined with a film or a shading device, Magnetite is the ideal solution for the hot Australian conditions.

Glazing Type Cooling Stars Heating Stars Cool% Heat% Uw SHGC AI
Double Glazed 5mm Supertoned glass/6mm
air gap/5mm clear glass IGU (Insulated Glass Unit)*		 blue starblue starblue starhalf blue star red starred starred starred starhalf red star 54% 425% 3.30 0.461 5.0
Single glazed 3mm glass Solartite**
and 4.5mm Magnetite		 blue starblue starblue starblue starblue starhalf blue star red starred starred starred star 73% 38% 2.4 0.19 0.5

 

*WERS standard typical industry window
**Solartite is a range of high performance window film. The window tested above has Solartite’s low-e film.

Click here to view pdf version of Magnetite WERS test result.

Noise Reduction Technical Data and Results

Proven Results

Noise pollution is one the biggest problems faced in the cities today, particularly in a high-density living. Unwanted noise can be responsible for sleep loss and lack of concentration. This can lead to a deterioration of health through increased stress levels, headaches, high blood pressure and loss of hearing.

Noise penetrates windows through leaky seals or vibrations through the window structure. To reduce noise, a window should minimise air infiltration, hold enough weight to limit vibration and allow a large air cavity. This cavity, or air gap, is the key to secondary glazing.

Expert Advice:

CSIRO Research by John Davy shown an air cavity can effectively enhance sound insulation performance. The larger the air cavity the more noise the window system can reduce. Results show a wide air gap of 100-125mm will improve sound insulation by an average of 7dB(A) more than windows with a narrow gap of 8-13mm.

Window or Glass Door Type Total Glass Thickness (mm) Air Cavity Thickness (mm) Sound Insulation (dB)
Single Glaze 3mm 3 0 23
Single Glaze 6mm 6 0 27
Double Glaze Narrow Gap 9-12 8-13 31
Double Glaze Wide Gap 9-12 100-125 38

 

The human ear is less sensitive to low frequency sound. According to a study released by the CSIRO, the human ear needs a change of 3dB to detect a difference in noise levels and the human ear perceives a change of 10dB as a doubling or halving of the noise level.

If you double the thickness of glass in a window the noise level will decrease by 3dB the least amount possible to make a difference. If the glass is laminated there is no perceived difference in noise reduction.

National Acoustic Laboratory Testing:

Working with the principles of noise transfer, Magnetite® and Soundtite are designed for high performance, which is achieved by combining air tight seals with the ability to maximize an air cavity and the flexibility to vary glazing thickness to suit. Magnetite® is excellent at reducing general noise such as busy roads, commuter trains and noisy neighbours. Whereas, Soundtite works well to combat low frequencies noise such as garbage truck, freight trains or airplane during take-off and landing.

Test Code Material Tested Rw* Improvement
ATF 707 (test window) Aluminium sliding window, 3mm float glass with mohair seals 23 N/A
ATF 709 Test window, 100mm air gap and Magnetite System (4.5mm acrylic panel) 35 52%
ATF 1507 Test window, 100mm air gap and Magnetite System (10.0mm acrylic panel) 39 70%
ATF 817 Test window, 100mm air gap and Soundtite (6.38mm laminated glass) 41 78%

 

*The Weighted Sound Reduction Index (Rw) is a measure for sound insulation performance of a single building element such as windows. The higher the Rw rating, the better the sound insulation.