London · Q2 2026
Double Glazing in
London.
Double glazing specs — what you actually get
The sealed unit specs we fit as standard across all uPVC and aluminium windows. Stripped-down "starter" glass is not something we offer — even our entry spec is A+ rated.
| Property | Standard | Upgrade available |
|---|---|---|
| Unit thickness | 28 mm (4–20–4) | 36 mm triple (4–12–4–12–4) |
| Glass type | 4mm toughened float | Laminated / acoustic |
| Cavity gas | Argon 90% fill | Krypton |
| Low-E coating | Planitherm / Pilkington K | Solar-control SN62 |
| Spacer | Warm edge Super Spacer | — |
| U-value (glass) | 1.0 W/m²K | 0.6 W/m²K (triple) |
| U-value (whole window) | 1.2 W/m²K | 0.85 W/m²K (triple) |
| Energy rating | A+ | A++ |
| Acoustic (Rw) | 31 dB | 40 dB (laminated acoustic) |
| Guarantee | 15 years sealed unit | — |
Glass options by use case
Standard Low-E Argon-filled double glazing is the right spec for 80% of London homes. The other 20% need a specific glass upgrade — here’s what goes where.
| Scenario | Recommended glass | Premium |
|---|---|---|
| Typical semi / terrace | Standard A+ Low-E Argon | + £0 |
| West-facing summer overheating | Solar control (SN62 coating) | + 8–15% |
| Main road / flight path | Laminated acoustic (6.8mm laminated outer) | + 20–30% |
| Ground floor security | Laminated inner (6.8mm) | + 15–20% |
| Bathroom / privacy | Obscure level 3–5 | + 5–10% |
| Listed building (appearance) | Slim-line Planitherm with astragal bars | + 10–20% |
| Passivhaus / net-zero | Triple glazed with Krypton fill | + 35–50% |
Double vs triple glazing — when to upgrade
Triple glazing costs 35–50% more than double for a ~30% thermal improvement. It pays back over 15–20 years in typical London properties. Here’s when it’s worth it.
| Factor | Double glazing (standard) | Triple glazing |
|---|---|---|
| U-value (whole window) | 1.2 W/m²K | 0.85 W/m²K |
| Unit thickness | 28 mm | 36 mm |
| Weight per m² | ~20 kg | ~30 kg |
| Cost vs double | Baseline | + 35–50% |
| Heat loss reduction vs DG | — | ~30% less |
| Annual energy savings (3-bed semi) | — | £40–£90 |
| Payback period | — | 15–20 years |
| Best for | Most homes | New build, deep retrofit, acoustic + thermal |
Double glazing cost breakdown
Fitted prices in London, Q2 2026, for our standard A+ double glazing spec. Prices are per window including VAT, frame, glass, fitting, and FENSA self-certification.
| Window type | Frame | Low | High |
|---|---|---|---|
| Casement (1200 × 1200) | uPVC | £550 | £900 |
| Casement (1200 × 1200) | Aluminium | £900 | £1,500 |
| Flush casement | uPVC Heritage | £650 | £1,400 |
| Flush casement | Aluminium | £1,100 | £2,000 |
| Sliding sash | uPVC Liniar | £900 | £1,800 |
| Tilt & turn | uPVC | £700 | £1,500 |
| Tilt & turn | Aluminium Schüco | £1,100 | £2,200 |
| Bay window (3-piece) | uPVC | £1,800 | £3,500 |
| Bay window (5-piece) | uPVC | £2,500 | £4,500 |
| Whole house (8 windows) | uPVC mixed | £5,500 | £10,000 |
| Whole house (8 windows) | Aluminium | £8,500 | £18,000 |
Frequently asked
How much does double glazing cost in London in 2026?
Standard A+ double glazed windows in London cost £550–£1,200 per uPVC casement or £900–£1,800 per aluminium casement, fitted. A whole-house replacement of 8 windows runs £5,500–£10,000 in uPVC or £8,500–£18,000 in aluminium. Prices include VAT, FENSA self-certification, and 15-year sealed unit guarantee.
What U-value do A-rated double glazed windows have?
Our standard A+ double glazing achieves 1.2 W/m²K whole-window U-value with 28mm sealed units (4mm glass, 20mm Argon-filled cavity, Low-E coating, warm-edge spacer). Current UK Building Regs require maximum 1.4 W/m²K for replacement windows — our standard spec exceeds that by ~14%.
How long does double glazing last?
Modern double glazed sealed units last 20–25 years before the cavity gas dissipates and condensation can form between panes. Our sealed units come with a 15-year guarantee against misting and seal failure. uPVC frames last 25–30 years; aluminium 30–40 years.
Double glazing vs triple glazing — which is worth it?
Triple glazing costs 35–50% more than double for ~30% less heat loss. For a typical 3-bed London semi that’s £40–£90/year savings, paying back over 15–20 years. Worth it for: new-builds, deep retrofits aiming for net-zero, Passivhaus spec, or properties needing both acoustic and thermal upgrade. Not worth it for typical replacements.
What is A-rated and A+ rated glazing?
The Window Energy Rating (WER) is a UK standard from A++ (best) to E (worst). A+ windows have U-value 1.2 W/m²K or lower. A++ achieves 0.85 W/m²K (typically triple glazed). All windows we fit are A-rated as standard, A+ with any upgrade.
Does double glazing reduce noise?
Standard A+ double glazing achieves 31 dB noise reduction (Rw). Acoustic laminated double glazing (6.8mm laminated outer pane) hits 38–40 dB — enough for properties near main roads or flight paths. Triple glazing adds another 2–5 dB but the laminated upgrade is more cost-effective for acoustics alone.
Can old single-glazed windows be upgraded without full replacement?
In listed buildings where replacement isn’t permitted, secondary glazing (an independent inner pane added to the existing window) reaches U-value 1.8–2.2 W/m²K — not as good as full double glazing at 1.2 but avoids planning complications. For everything else, full replacement is the right answer.
What is Low-E glass?
Low-emissivity (Low-E) glass has a microscopic metallic coating on the inner-cavity surface that reflects heat back into the room in winter and blocks solar gain in summer. It’s standard on every window we fit (Saint-Gobain Planitherm or Pilkington K). Adds no visible tint.
Is Argon gas fill worth it?
Yes — and it’s standard on every sealed unit we fit. Argon (90% fill) between panes has lower thermal conductivity than air, improving U-value by ~15%. Zero cost difference vs air-filled units. Krypton gas is marginally better but 3–4x the cost and rarely justified.
How do I know if my double glazing has failed?
The three signs: (1) condensation or misting between panes (cavity seal gone), (2) cold spots near window edges in winter, (3) visible draughts from frame. Failed sealed units can usually be replaced without replacing the whole frame — our replacement-only service costs £180–£320 per unit depending on size.
