Single, Double or Triple Glazing: How to Choose

Glazing accounts for 70 to 80 % of a window’s surface area, and it is therefore what determines the essential thermal, acoustic and light performance of the whole window unit. Between single glazing — now banned in new builds — low-E argon-filled double glazing that has become the RE2020 standard, and triple glazing reserved for high-performance homes, the choice comes down to a handful of indicators (Ug, Sw, g, Rw) that can seem obscure at first. This guide breaks down glazing technology, compares each family across 6 criteria, details gas filling and low-emissivity coating options, and gives you the decision rule for choosing the right glazing for south-facing, north-facing, street-side or garden-side openings.

Understanding glazing: much more than just glass

Modern glazing is not “just glass”. It is a technical assembly in which each layer plays a precise role: insulating, letting light through, filtering sun, damping noise, resisting impacts. On a 120 × 120 cm window, the glazed surface is 1.2 m² out of 1.44 m² total — the frame and sash cover only 15 to 25 % of the area, the rest is all glazing. Hence the importance of knowing what you are looking at.

Key indicators to know before ordering

Every glazing unit is characterised by a series of standardised coefficients which must appear on the manufacturer’s data sheet. Knowing how to read them means being able to compare two quotes or talk to a window supplier without being misled.

• Ug (Uglass, in W/m².K) — The thermal transmittance of the glazing alone. The lower it is, the better the glazing insulates. Single glazing: 5.8. Standard double: 2.8. Low-E argon double: 1.1. Triple low-E: 0.5 to 0.7.
• Uw (Uwindow, W/m².K) — Coefficient for the complete window unit (glazing + frame + spacer + thermal bridge). This is the regulatory value under RE2020. Always higher than Ug.
• Sw (or g for the glazing alone, from 0 to 1) — Solar factor. The proportion of solar energy that passes through the glazing. A Sw of 0.6 means 60 % of solar energy is transmitted — useful in winter, penalising in summer on an unshaded south facade.
• TL (Light Transmittance, from 0 to 1 or as %) — Proportion of visible light transmitted. A TL of 0.80 = 80 % of light passes through. Important for visual comfort and free solar gains in winter.
• Rw (in dB) — Sound reduction index. Standard double glazing achieves 30–32 dB. An asymmetric acoustic glazing unit 4/16/10 reaches 38–42 dB.
• Cl.A/B/C (impact resistance) — Safety classification per EN 12600. Mandatory in balustrades, recommended in low-level picture windows.

Single glazing: the relic you must not use in new builds

Single glazing is a single sheet of float glass, 3, 4, 6, 8 or 10 mm thick, with no air gap or treatment. Its Ug of 5.8 W/m².K makes it a thermal sieve: a 2 m² pane loses nearly 300 W on its own with 20 °C inside and 0 °C outside — equivalent to an average electric panel heater running continuously.

Where it is still found

• Unrefurbished older buildings — many pre-1980 homes still have original single glazing
• Unheated outbuildings — garage, workshop, garden shed (perfectly acceptable there)
• Roof glazing such as greenhouses or uninsulated verandas — horticulture, pergolas
• Inner doors, draught lobbies where some heat loss is accepted because a second heated window is behind

Why it is banned in new builds

RE2020 (French environmental regulation 2020) requires a maximum Uw of 1.3 W/m².K for windows in new residential buildings, which single glazing can never achieve regardless of the frame. In practice: you will no longer find any manufacturer offering a new window with single glazing for a dwelling. You only need to look into it if you are renovating an older building and need a like-for-like replacement — and even then, MaPrimeRénov’ grants will require you to upgrade to low-E double glazing as a minimum.

Low-E argon double glazing: today’s standard

Low-emissivity argon-filled double glazing (known in France as ITR or VIR) is the absolute standard for new residential builds in 2026. It is the default assembly for every window delivered in a new RE2020 home.

Typical composition 4/16/4 argon

• Outer pane: 4 mm clear float glass
• Warm-edge spacer: polymer or stainless steel profile, 16 mm wide, holding the two panes parallel and sealing the cavity
• Argon gas filling the space (90 % minimum — argon is 33 % less conductive than air)
• Low-E coating (low-emissivity film) sputter-deposited on face 3 (internal face of the inner pane, argon side) — nanometre-thin metallic oxide layer that reflects infrared radiation
• Inner pane: 4 mm clear float glass
• Butyl sealant + polysulphide or silicone sealant around the perimeter, ensuring gas-tightness for 20 to 30 years

The result: Ug 1.1 W/m².K (vs 5.8 for single), Sw 0.62, TL 0.80, Rw 32 dB. Performance that was top-of-the-range 15 years ago is now the entry-level option.

Useful variants

• 4/20/4 argon — 20 mm gas cavity instead of 16, marginal Ug gain (1.0 instead of 1.1)
• 4/16/4 krypton — Krypton instead of argon, Ug 0.9. More expensive (krypton costs 10× more than argon), useful on small panes where total thickness is constrained
• 4/16/6 or 6/16/4 (asymmetric) — Thicker glass on one side for better acoustics, Rw 36–38 dB
• Additional face 2 low-E coating — Double low-emissivity layer to reach Ug 0.9 without going triple
• Solar control glazing (e.g. Planitherm 4S, Cool-Lite) — Selective film filtering solar infrared, Sw drops to 0.35 — useful on south facade without an overhang

Triple glazing: when do you really need it?

Triple glazing adds a third central pane, creating two argon gas cavities (2 × 16 mm) and two low-E coatings (faces 2 and 5). The result: a Ug of 0.5 to 0.7 W/m².K — twice as good as low-E double and almost ten times better than single.

What it brings

• Exceptional thermal insulation — half the heat loss of double glazing
• Winter comfort: the internal glazing surface stays at 18–19 °C instead of 14–15 °C for double, eliminating the “cold wall” draught effect
• Slightly better acoustics (Rw 35 dB vs 32) — but an asymmetric acoustic double unit performs equally well for less money
• Compatible with Passivhaus and positive-energy homes — these labels require Uw < 0.85, achievable only with triple

What it costs (in the broadest sense)

Triple glazing is not just a better double — it is a technical choice with trade-offs. Before ordering, understand its limitations:

• Price: 180 to 320 €/m² of glazing vs 80–150 for low-E double, i.e. ×2 to ×2.5
• Weight: 30 kg/m² instead of 20 — reinforced hardware mandatory, sometimes impossible to fit on older lightweight frames
• Solar factor g = 0.50 instead of 0.62 — free solar gains reduced by 20 %, negative impact on south facade in winter (you heat more to compensate)
• TL = 0.72 instead of 0.80 — 10 % less light, rooms slightly darker
• Thickness of 44 mm — requires a deep frame (> 70 mm), limits profiles and retrofitting
• Questionable economic return in mainland France — the premium only pays back in very cold climates (mountain areas, north-east) or predominantly north-facing facades

Visual comparison of the three families

How low-E glazing works

ITR (enhanced thermal insulation) performance comes from three combined innovations:

1. The fill gas

Ordinary dry air has a thermal conductivity λ = 0.025 W/m.K. By filling the cavity with argon (λ = 0.018), you gain 30 %. Krypton (λ = 0.009) does even better but costs 10× more — reserved for thin cavities (8–10 mm) where the benefit per mm of thickness is highest. Xenon also exists (λ = 0.0055) but at an extreme price, used only in aerospace glazing.

The fill rate must be ≥ 90 % (measured at the factory, CEKAL certified). Gas leaks at 0.5 to 1 % per year through the seals: an argon-filled unit loses 20 to 30 % of its charge over 30 years — it remains effective but does age.

2. The low-emissivity coating (low-E)

A deposit of metallic oxide at nanometre thickness (< 100 nm) sputtered onto one of the internal faces of the glazing unit. Invisible to the eye, this coating reflects the infrared radiation emitted by warm bodies (your radiator, your body) instead of letting it escape outward. It blocks very little visible light: TL drops from 90 % (bare glass) to 80 % (low-E face 3), which remains very bright.

The coating is extremely fragile — it must stay sealed inside the gas cavity, never on an exposed outer face. That is why you cannot add a low-E coating to an existing unit without complete remanufacture.

3. The warm-edge spacer

The spacer bar separates the two panes and seals the gas cavity. Old-style aluminium spacers conduct heat like a motorway and create a peripheral thermal bridge: you often see condensation at the bottom of windows fitted with aluminium-spacered double glazing in deep winter. Warm-edge spacers (polymer + thin stainless steel strip) divide this thermal bridge by 3 to 5 and improve the Uw by 0.1 to 0.2 points. This is a recent development (2010s), standard today but not always included in budget units — worth checking.

Specialist glazing: safety, acoustic, self-cleaning

Beyond the thermal-light pairing, certain situations call for functional specialist glazing.

Safety glazing

• Toughened glass — heated to 650 °C then rapidly cooled. Impact resistance ×5, shatters into small non-cutting fragments. Mandatory in doors, low-level patio doors, transoms.
• Laminated glass (type 33.2, 44.2, 44.6) — two or three panes bonded by PVB interlayer film. Holds together after breakage, stays in place. Mandatory in balustrades, roof lights, cills below 1.00 m. Coded as fractions: 44.2 = two 4 mm panes + two PVB films; 55.4 = two 5 mm panes + 4 PVB films (thicker, stronger).
• Anti-intrusion glass — reinforced laminates (classes P1A to P8B per EN 356), resistant to hammer and crowbar. Recommended at ground-floor level.

Acoustic glazing

An asymmetric double unit with a thicker inner pane (4/16/10 or 6/16/10) and an acoustic PVB interlayer achieves Rw 38 to 42 dB, against 32 for a standard double unit. An audible gain of 6 to 10 dB — perceived noise halved to quartered. Justified on facades facing a busy road, railway line or airport.

For even higher performance, laminated acoustic glazing such as SGG Stadip Silence or equivalent (Saint-Gobain, Guardian, Pilkington UK) reaches 45–47 dB.

Self-cleaning glazing

A titanium oxide coating on face 1 (external) which, under UV light, breaks down organic soiling and makes the surface hydrophilic — rainwater sheets off in a film rather than droplets, carrying dirt away. Useful on hard-to-reach facades (high-level glazing, large picture windows). Extra cost: 20–40 €/m². Genuinely effective, though not miraculous — a half-yearly clean is still recommended.

Solar control glazing

For south or west facades with large glazed areas and no solar overhang, solar control glazing (Saint-Gobain Cool-Lite, Pilkington Suncool, Pilkington Activ Blue) selectively filters solar infrared radiation. Sw drops to 0.3–0.4, TL remains at 0.55–0.70. Summer overheating is avoided while good daylighting is maintained.

Which glazing for which situation?

The choice depends on three variables: orientation of the opening, local climate and noise environment. Here is the decision matrix to apply opening by opening.

Practical rules by room

Regulatory requirements

RE2020

RE2020 (French environmental regulation 2020) applies to all new construction since 2022. At window level it requires:

• Uw ≤ 1.3 W/m².K in new residential buildings (glazing + frame combined)
• Air permeability class A*3 minimum (frame-to-sash airtightness)

The glazing alone is not regulated in isolation — it is the combined Uw that counts — but to reach 1.3 you need a Ug ≤ 1.1 as a minimum. For more detail on the implications, see our guide understanding RE2020 in self-build.

Glazing standards

• EN 1279 — insulating glass units: airtightness, durability, performance
• EN 12600 — impact resistance classification (1B1 minimum in balustrades)
• EN 356 — resistance to manual attack (P1A to P8B)
• EN 12150 — toughened glass
• EN 14449 — laminated glass
• CEKAL — French certification for gas fill rate and durability (per-batch certificate, valid 10 years)

Glazing prices in 2026

Price ranges for 2026 for glazing only (to add to the window frame cost). Window suppliers invoice the complete unit, but the “glazing” element breaks down approximately as follows:

Budget for a standard new build

For a 110 m² home with 8 windows + 1 picture window + 1 French window = approximately 22 m² of total glazing, budget:

• Standard RE2020 low-E argon double: 1,800 to 3,300 € glazing premium (total window cost 5,500 to 11,000 €)
• Full triple glazing: 4,000 to 7,000 € glazing premium (total window cost 12,000 to 22,000 €)

Maintenance and service life

A well-manufactured argon double unit lasts 25 to 40 years. Beyond that, seals age, gas escapes and micro-condensation appears in the cavity (the sign that replacement is needed). Standard manufacturer warranty is 10 years (CEKAL certification), some manufacturers such as AGC or Saint-Gobain offer up to 15 years.

End-of-life signs

• Permanent misting between the two panes (not on the inside or outside surface, but inside the unit)
• Dust or crystals visible in the gas cavity
• Abnormally cold surface (finger on the inner pane in winter at -5 °C outside: below 13 °C = warning sign)

Replacement

When renovating, replacing the glazing alone (without changing the frame) is only possible on a compatible, correctly-sized existing frame. Otherwise, the complete window must be replaced. Budget 150–300 €/m² for replacement glazing fitted only.

Common mistakes to avoid

1. Installing triple glazing due south without considering Sw → you lose free winter solar gains and heat more as a result
2. Buying “double glazing” without specifying low-E and argon → you end up with 4/16/4 air, Ug 2.8, 1995-level performance
3. Forgetting the warm-edge spacer → peripheral thermal bridge, condensation at the bottom of the unit, Uw degraded by 0.1 to 0.2
4. Choosing thick glazing in a frame that is too shallow → the frame cracks, the unit does not fit, removal and refitting at your expense
5. Single glazing in a heated conservatory → summer overheating and winter heat loss make the room unusable
6. No toughened glass above a door transom → serious injury risk in the event of breakage, liability implications
7. Forgetting laminated glass in a balustrade → non-compliance with NF P01-012, likely non-acceptance
8. Missing CEKAL certification → unable to prove Ug and argon fill rate, grants refused
9. Confusing Ug and Uw → Uw (complete window) is always worse than Ug (glazing alone) by 0.2 to 0.5 points
10. Triple glazing on hardware rated for double → hinges wear out in 2 years, sashes drop

Useful links and reference manufacturers

• Saint-Gobain Glass — SGG Planitherm low-E range — European leader, comprehensive data sheets
• AGC Glass Europe — Energy N, Stopray range
• Pilkington UK — Optitherm, Suncool, Activ range
• Guardian Glass — ClimaGuard, SunGuard
• CEKAL — insulating glass unit certification — certified products database
• CSTB — Technical Approvals for glazing
• French Ministry of Ecological Transition — RE2020

Checklist before ordering your glazing

Further reading

• Before choosing your glazing, define your frame material with our guide choosing windows: PVC, aluminium or timber
• Once the glazing is chosen, move on to fitting a double-glazed window yourself
• To optimise the overall design, consider passive solar orientation — great glazing facing south without an overhang wastes bioclimatic potential
• Check the overall requirements of RE2020 in self-build
• Window sills and exterior thresholds are prepared in parallel — perfect glazing cannot compensate for a poorly-made sill