Double Glazing vs Secondary Glazing for Old Adelaide Homes
Secondary glazing adds a slim second pane inside your existing window rather than replacing the glass, so the original window stays untouched. For old and heritage Adelaide homes it is often the smarter choice: it costs less than true double glazing (commonly $250 to $600 per window), preserves the original timber sashes and leadlight, and usually sidesteps heritage overlay approval because nothing on the outside changes. True double glazing performs a little better thermally and looks fully integrated, but it is dearer and can trigger overlay rules on a listed facade. For character homes in Unley, Norwood or Prospect, secondary glazing frequently wins on cost, heritage compliance and reversibility.
Key takeaways
- Secondary glazing adds an internal pane; true double glazing replaces the glass with a sealed unit.
- Secondary glazing is cheaper, roughly $250 to $600 per window versus $400 to $1,800 for double glazing.
- It preserves original sashes and leadlight, which matters for character and heritage homes.
- It usually avoids heritage overlay approval because the external appearance is unchanged.
- True double glazing performs slightly better and looks integrated, but costs more and can trigger overlay rules.
What secondary glazing is and how it differs
Secondary glazing fits an additional pane, usually in a slim aluminium or timber sub-frame, on the inside of your existing window. Your original single-glazed sash stays exactly as it is, and the new pane creates a captive air gap in front of it. That air gap is what delivers the insulation and noise reduction, the same principle as double glazing, achieved without touching the original glass.
True double glazing, by contrast, removes the single pane and fits a factory-sealed double-glazed unit, either into the existing frame (retrofit) or a new frame (full replacement). The sealed unit has argon or dry air and a spacer bar, and it becomes the window. The original glass is gone.
The key practical difference is that secondary glazing is additive and reversible, while double glazing changes the window itself. For a heritage sash with wavy old glass or a leadlight panel, that distinction decides whether you keep the original feature or lose it.
Cost, heritage rules and the character-home case
On cost, secondary glazing typically runs $250 to $600 per window, below retrofit double glazing and well below full replacement. For a character home with many windows, that gap adds up quickly across the whole house.
On heritage rules, secondary glazing has a real advantage. Because it sits inside and changes nothing about the external appearance, it generally does not need development approval under a heritage overlay, whereas altering the actual windows on a listed or contributory facade often does. Adelaide councils covering Unley, Norwood Payneham St Peters and Prospect have overlays that protect original streetscapes, and anything visible from the street can require consent. Always confirm with your council, but internal secondary glazing is the lower-friction path.
On performance, true double glazing edges ahead because its gap is sealed and gas-filled, while a secondary pane relies on a captive but not hermetically sealed air layer. In practice, for comfort and noise in a character home, secondary glazing delivers most of the benefit at lower cost and lower approval risk, which is why it is so often the right answer for old Adelaide homes.
Choosing between them for your home
Choose secondary glazing if keeping the original sashes, leadlight or wavy glass matters to you, if the window is on a heritage-protected facade, or if budget is the deciding factor. It is also ideal for noise, since a larger air gap between the secondary pane and the original often beats a narrow sealed unit for cutting low-frequency traffic rumble.
Choose true double glazing if the original windows are already gone or unremarkable, if you want the tightest thermal performance, or if you are renovating and replacing the windows anyway. On a non-heritage 1970s home, retrofit double glazing is usually the cleaner choice.
Many character-home owners end up combining approaches: secondary glazing on the protected street-facing windows to keep the look, and retrofit double glazing at the rear where appearance is not restricted. We connect you with vetted local specialists who understand Adelaide heritage overlays and will quote both options, so you can compare quotes and protect both your comfort and your home's character.
Ready to get real numbers? Compare 3 free quotes from vetted Adelaide specialists for double glazing.
Frequently asked questions
For comfort and noise it is close, and for low-frequency traffic noise a wide secondary air gap can even beat a narrow sealed unit. True double glazing performs slightly better thermally because its gap is sealed and gas-filled.
Usually not, because it is internal and changes nothing visible from the street. That is a major reason it suits heritage-overlay homes in Unley, Norwood and Prospect, though you should always confirm with your local council.
Commonly $250 to $600 per window, which is less than retrofit double glazing and well below full replacement. For a character home with many original windows, that saving across the house is significant.