Double glazed gets thrown around like it means one thing. It does not. There is thermal double glazing (designed to keep heat in in winter and out in summer) and there is acoustic double glazing (designed to block sound), and the two specifications are noticeably different. Pick the wrong one and you spend the money without solving the problem.
Thermal double glazing, what it actually is
An insulated glass unit (IGU) with two panes of standard float glass separated by a spacer bar, with dry air or argon gas trapped between them. Typical residential spec: 4 mm glass, 12 mm argon-filled gap, 4 mm glass. Total assembly 20 mm thick.
The insulating work is done by the gas gap. Argon conducts heat about a third slower than air, which is why it is used in almost every quality IGU. Add a Low-E coating to one face of the inner pane and the assembly reflects radiant heat back where it came from as well, cutting summer heat gain and winter heat loss further.
A standard 4-12-4 argon-filled IGU with Low-E gives a U-value of around 1.6 to 1.9 W/m2K. Compared to a single 4 mm pane at U 5.8, that is roughly a 3x improvement in thermal insulation.
Acoustic double glazing, what changes
An acoustic IGU keeps the two-pane structure but changes three things:
- Different pane thicknesses. Two identical panes resonate together at the same frequency, which is bad for sound reduction. Mixing pane thicknesses (say 6 mm on one side and 4 mm on the other) breaks the resonance and improves broad-band performance.
- Laminated glass on at least one face. The PVB interlayer inside laminated glass absorbs vibration. Acoustic-grade PVB is optimised specifically for sound damping.
- Wider gap. Where thermal IGUs are optimised for a 12 to 16 mm gap, acoustic IGUs benefit from a wider gap, typically 16 to 20 mm.
A typical acoustic spec we quote: 6.38 mm acoustic laminate plus 16 mm argon plus 4 mm float. Total assembly 26 mm thick, Rw around 40 dB, U-value around 1.8.
Where they overlap, and where they do not
Thermal IGUs give you some acoustic reduction, roughly Rw 28 to 32 dB, which is meaningfully better than single glazing (Rw about 25 dB). Acoustic IGUs give you some thermal benefit but they are heavier and thicker, which usually means the frame has to be upgraded to a larger extrusion.
Bottom line: if your primary problem is comfort (a west-facing room that overheats in summer, a room that is freezing in winter, an energy bill you want to cut), thermal is the right spend. If your primary problem is noise (aircraft, traffic, trains), acoustic is the right spend. If both, we quote a hybrid spec that leans toward whichever is more critical.
How to decide for your Penrith home
Three quick questions:
- What is your worst month for comfort? Summer (west-facing overheating), winter (cold bedrooms), or year-round?
- Can you hear neighbours, traffic, or aircraft from inside with the windows closed?
- What is the primary use of the room you are upgrading? Sleeping, working, watching TV, entertaining?
Answers to those three usually make the specification obvious. A west-facing bedroom under the flight path is a hybrid job (acoustic laminate plus Low-E). A north-facing living room with no noise problem is pure thermal. A south-facing study near a noisy road is pure acoustic.
The Low-E overlap
Low-E is a thermal upgrade. It does not affect acoustic performance either way. So a Low-E acoustic IGU is possible and gives you both benefits at a modest premium over base acoustic. If you can afford it, we recommend Low-E on any acoustic spec in west-facing or north-facing rooms because you are already replacing the glass.
Frame matters, and often does not get specified
The best IGU in the world will underperform in a leaky frame. Any upgrade project should include:
- New continuous seals at head, jambs and sill.
- Acoustic backer rod around the frame perimeter if acoustic performance is critical.
- A frame profile rated to handle the IGU weight without deflection over time.
Our standard aluminium window and door range covers frame profiles suitable for every glass upgrade we quote. See the full range on the Windows and Doors overview, and the awning window configurations which are our default for acoustic-critical rooms.
Cost comparison
For an 1800 x 1200 mm bedroom awning:
- Standard double glazed thermal: $900 to $1,300 supplied and installed.
- Thermal with Low-E: $1,100 to $1,500.
- Acoustic IGU: $1,400 to $2,000.
- Hybrid (acoustic laminate plus Low-E): $1,700 to $2,300.
These are indicative for Penrith metro. Custom sizes and colours push the numbers up. Retro-fit into an existing sash where possible drops them by roughly 30 percent.
Same-day quote
Photo of your existing window plus rough dimensions and the room’s primary problem, sent through the contact form, gets you a firm number back the same day during business hours.
