Glass: the most important element of your window
When we think about windows, we tend to focus on the profile (PVC, aluminium, wood) and forget that glass makes up 70-80% of the window's surface. It's through the glass that most thermal energy is lost (or gained).
Choosing the right glass can make an enormous difference to thermal insulation, acoustic insulation and your home's security. At Instal Tancaments, after over 25 years installing PVC windows in Girona, we've seen how good glazing transforms a home.
Types of window glass
1. Double glazing — The current standard
Double glazing consists of two panes of glass separated by an air or gas cavity.
Standard notation: 4/16/4 (4mm outer glass / 16mm cavity / 4mm inner glass)
Ug value: 2.7 W/m²K (air) / 2.5 W/m²K (argon)
Indicative price: from €40-60/m²
2. Low-emissivity glass (Low-E) — Most recommended
Low-E glass has an invisible metallic oxide coating that reflects interior heat back into the room. This is the type we most recommend for its performance-to-price ratio.
Typical notation: 4/20/6 Low-E
- The low-e coating reduces heat loss by radiation by 60-70%
- Ug value: 1.1 W/m²K — almost three times better than standard double glazing
- Not visually noticeable — the window looks the same
- Indicative price: from €55-80/m²
Our recommendation: for Girona's climate (climate zone C), Low-E 4/20/6 glass offers the best value for money.
3. Solar control glass (SC) — For south and west-facing
Solar control glass combines the low-e coating with a treatment that reduces solar radiation entry.
- Reduces solar heat entry by 40-60%
- Maintains brightness (visible light factor > 70%)
- Ug value: 1.1 W/m²K + solar factor g < 0.42
- Indicative price: from €70-100/m²
Watch how solar rays hit the glass and what percentage is reflected, absorbed and transmitted.
See how acoustic laminated glass reduces exterior noise down to comfort levels.
- Reduces exterior noise 30-40% more than standard double glazing
- Also provides security — if broken, fragments stick to the interlayer
- Acoustic insulation: up to 42-45 dB
- Indicative price: from €80-120/m²
5. Triple glazing — Maximum insulation
Triple glazing adds a third glass pane and a second cavity. It's the standard in Passivhaus construction.
- Ug value: 0.5-0.7 W/m²K — the best insulation possible
- Ideal for cold areas and maximum energy efficiency projects
- Greater weight — requires reinforced hardware
- Indicative price: from €100-150/m²
6. Safety glass — For ground floor and children
Safety glass can be toughened (breaks into small non-sharp fragments) or laminated (fragments stick to the interlayer).
- Required by regulations on accessible ground floors and glass doors
- Highly recommended with young children
- In second homes provides anti-burglary security
- Indicative price: €15-30/m² surcharge over standard glass
Glass comparison: insulation and price
| Glass type | Ug (W/m²K) | Acoustic (dB) | Price from (€/m²) | Ideal for |
|---|
| Standard double 4/16/4 | 2.7 | 30 | €40 | Minimum budget |
| Double Low-E 4/20/6 | 1.1 | 32 | €55 | Best all-round option |
| Double Low-E+SC 4/20/6 | 1.1 | 32 | €70 | South/west facing |
| Laminated acoustic 4+4/16/6 | 1.1 | 42 | €80 | Noisy areas |
| Triple 4/16/4/16/4 Low-E | 0.6 | 35 | €100 | Passivhaus, max insulation |
| Safety (toughened/laminated) | Varies | Varies | +€15 | Ground floor, children |
Which glass to choose? Our recommendation
- For most homes: double Low-E 4/20/6 — the best value for money
- South/west facing with lots of sun: add solar control — 4/20/6 Low-E SC
- Noisy street or tourist area: laminated acoustic — 4+4/16/6 Low-E
- Maximum efficiency or Passivhaus: triple glazing with argon
- Ground floor or with children: add safety glass
Try our price calculator to see how the price changes depending on the glass type you choose.
Is argon gas worth it?
Argon gas is an inert gas that replaces air in the double or triple glazing cavity.
- Improves Ug by 10-15% compared to air
- The additional cost is minimal (€10-15 per window)
- Our opinion: yes, it's worth it. The extra cost is insignificant for the improvement it provides
Frequently asked questions
Can you change just the glass without changing the window?
In some cases yes, if the window profile has sufficient rebate to accommodate thicker glass. But if your windows are old, it's usually better value to change the complete window.
How much do you save on heating with good glass?
Upgrading from single glass to double Low-E can reduce heat loss through windows by 60-70%. In an average home in Girona, this means savings of €200-400/year on heating.
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