Double Glazing will Save Energy Costs.
Warmer in winter & cooler in summer.

Save on heating & cooling costs with secondary double glazed insulated windows
The highest quality secondary double glazing for window insulation to save energy costs

SoundProof Windows & Doors. Secondary glazed windows save energy costs



Our highly  energy efficient retrofitted thermal glazed windows help maintain your rooms temperature & the additional seals around the new windows or doors eliminate drafts & air leakage.

The best energy saving windows and doors Melbourne has to offer.

If you’re here because you want to know how to insulate windows or you’re simply looking for more energy-efficient windows, you should know that … up to 40% of all heat loss in a home or building is through the windows. Our secondary glazing thermally efficient windows or energy efficient windows can very effectively insulate windows & stop up-to two thirds the heat loss you are currently experiencing through your windows!

For insulating windows or for providing energy-efficient windows, secondary glazing is one of the most cost effective window insulation solutions available in Melbourne today. The manufacturing & installation costs are lower than traditional double glazing & the thermal effieciencies due to the design approach provide significant additional thermal & heating &/or cooling cost benefits over alternative options such as PVC or insulating films.

The advantages of Secondary Double Glazing include more than just reducing noisesound proofing or sound reduction. Secondary Double Glazing also reduces heat loss, saves on heating & cooling costs, has less condensation, eliminates drafts and will likely increase your property value.

Retrofitted double glazing has better insulating properties than traditional double glazing because there is a larger insulating air gap between the panes of glass. Also, as we completely seal around the frame of the new door or window there is never any gap beween the frame and the walls, unlike as sometimes is the case with traditional double glazing.

And because we do not reeplace the exisitng windows, you can have thermally & energy efficient windows for relatively little outlay particluarly as compared to traditional double glazed windows, which is then recovered over the years by lower fuel bills as a result of your energy efficient windows!

Studies by the Australian Glass and Glazing Association on new homes built by one of Victoria’s biggest home builders showed an average cost payback of glazing windows to be just over five years on average. Please note that payback periods will vary depending on the initial costs, the type & amount of heating &/or cooling and therefore cost of energy used.

Additional Window Seals = More Energy Efficient Windows

It is also important to remember that a window allowing airflow around it will be a poor insulator, no matter what materials are used and its construction. Windows that have moving sections are highly likely to have gaps between the moving frame (sash) and the window frame.

So to properly insulate windows, we completely seal the new retrofitted secondary double glazed window frame, so there will be no airflow around the window. This  dramatically improves the thermal insulation properties of the window, provding you much improved window heat insulation.

The lower the ‘U’ Value the more energy efficient are the windows

The standard method of measuring windows energy efficiency is via the rate of heat loss through a window, which is called a ‘U value‘. A window with a U value of 4.0 W/m²K will lose twice as much heat as one with a U value of 2.0 W/m²K. The lower the ‘U value’, the more energy efficient is your window & the less heat you will lose through your windows. The table below shows how our energy saving windows compare to unmodified windows & traditional double glazed windows where the windows are completely replaced:

Window Glazing Options Glass – Gap – Glass U value
Single glazing: 3mm – 0mm – 0mm 5.9 W/(m².k)
Double glazing: 3mm – 6mm – 3mm 3.4 W/(m².k)
Secondary double glazing: 6.38mm – 100mm – 6.38mm 1.9 W/(m².k)

The U values for our secondary double glazing as shown in the table above show that if you’re thinking about thermally efficient windows or want energy efficient windows or want to know  how to reduce heat loss or gain through windows, or how to insulate windows, secondary double glazing is the clear winner! The numbers prove it!

And when combined with Sound Proof Window’s unique draft proofing properties, means that we offer the market leading solution for reducing heat loss, as well as window heat insulation & maintaining cooling from air conditioning units in summer. So if you want to convert existing windows to  energy efficient windows then retrofiting secondary double glazing will not only provide you with the the most energy efficient windows you can buy, but you will save typically at least 40% as compared to installing traditional double glazing.


  • Luminous and solar characteristics of glazing: EN 410 (1998)
  • Determination of UV, light and total solar transmittance: ISO 9050 (1990)
  • Determination of the thermal transmittance: EN 673 (1997)

Light Factor

  • Transmittance LT 69%
  • Outdoor reflectance LRE 18%
  • Indoor reflectance 16%

UV Factor

  • UV Transmittance TUV 27%

Energy Factors CEN (EN410)

  • Transmittance TW 53%
  • Outdoor reflectance RE 17%
  • Absorption A1 11%
  • Absorption A2 20%
  • Solar factor g 0.69
  • Shading coefficient SC 0.79
  • Solar factor g DIN 67507 (m1) 0.68

What do our customers say?

Here are some comments from our happy customers who have noted the thermal insulation benefits of our retrofitted double glazing solutions … click for more details.

Secondary Double Glazing = Energy Efficient Winows

For existing windows, secondary double glazing is the most energy efficient & cost effective window insulation solution for thermally efficient windows, termally glazed windows or energy efficient windows. In this day and age, with the ever increasing cost of energy for heating & cooloing, when you’re thinking about double glazing vs single glazing, the numbers stack up clearly.

If you require more information about what the science says are the best thermally efficient or energy efficient windows on the market, or, if you want a no obligation, free, on-site quote for secondary double glazed windows, please call us on 1300 127 173 or use our Contact Form to send us a message & we will arrange a time to visit you for a free no-obligation on-site quote.

We will take the time to explain how it works and why retrofitted or secondary double glazing is the best double glazing option for energy efficient windows for homes & buildings with existing windows & doors in Melbourne.