Choosing the glass
Glass makes up roughly 90% of a window, yet it is the most overlooked element. People focus on the frame material, when it is the glass that determines comfort, light, quiet and energy use. Here are the characteristics that really matter and how to choose the right glass.
The 4 characteristics that matter
- Thermal insulation (Ug, W/m²K): how much heat the glass loses.
- Acoustic insulation (Rw, dB): how much noise it blocks.
- Solar factor (SF/g): how much of the sun's heat it lets in.
- Light transmittance (LT): how much natural light it lets through.
Thermal insulation (Ug)
Thermal insulation is measured in W/m²K: it indicates how many Watts are lost per square metre for each degree of temperature difference. The lower the Ug value, the better.
A good double glazing (low-emissivity + argon gas) has a Ug of 1.0–1.1 W/m²K; a good triple glazing (two low-emissivity panes + argon) reaches 0.5–0.7 W/m²K.
| Type of glass | Ug (W/m²K) |
|---|---|
| Single pane | 5.8 |
| Insulated unit (double) | 2.7 |
| Double low-emissivity | 1.4 |
| Double low-emissivity + argon | 1.1 |
| Triple low-emissivity + argon | 0.6 |
Acoustic insulation (dB)
The higher the Rw value, the quieter the home. The choice should match the exposure: there's no need to fit the most sound-absorbing glass on the rear windows too.
| Context | Recommended glass |
|---|---|
| Quiet area | 36–37 dB |
| Slightly noisy area | 40–42 dB |
| Very noisy area (street-facing) | 44–48 dB |
Argon gas: +23% insulation
Filling the cavity with argon gas instead of air improves thermal insulation by about 23% (from ~1.3 to ~1.0 W/m²K on a double low-emissivity unit with a 16 mm cavity). It is non-toxic and costs little more: a performance-to-price ratio that should make it standard.
Spacer bar: Swisspacer “warm edge” only
The spacer bar runs along the perimeter of the insulated unit. The traditional aluminium one is conductive: it creates a thermal bridge and condensation at the edges. We use only Swisspacer warm-edge spacer bars, which cut heat loss by up to 60% and eliminate the thermal bridge.
Tip: don't accept proposals with aluminium spacer bars — they lose heat and guarantee condensation around the glass.
Double or triple glazing?
Balance always wins. If you have a poorly insulated wall, triple glazing achieves little: choose double. But if you plan external insulation or already have a good envelope, triple glazing is the right choice: more insulation, less noise, less condensation and more security.
Clear or extra-clear?
95% of glass has a slight green tint caused by iron. Extra-clear glass removes this impurity: more light (5–10% more), truer colours and superior looks. Recommended for balustrades, stairs and furniture, or in poorly lit rooms.
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