London · Q2 2026
Double vs Triple Glazing
The third pane changes five things
Triple glazing isn't just "double, but more". Adding a third pane changes the U-value, the acoustic rating, the weight, the cavity depth, and the payback economics. For most London projects in 2026, modern double glazing already delivers more than Building Regs requires. Triple glazing earns its premium in specific scenarios — Passivhaus, north-facing rooms, noisy roads, very large picture windows. Outside those, the spend is hard to justify on energy savings alone.
Spec comparison
Typical sealed unit construction for both, plus the performance numbers we test against on every Apex Glazing project.
| Spec | Modern Double | Triple |
|---|---|---|
| Unit construction | 4 mm – 16 mm – 4 mm | 4 mm – 12 mm – 4 mm – 12 mm – 4 mm |
| Total cavity | 24–28 mm | 36–44 mm |
| Cavity gas fill | Argon (90%+) | Argon or Krypton |
| Low-E coatings | 1 (soft-coat) | 2 (positions 2 + 5) |
| Centre-pane Ug | 1.0–1.2 W/m²K | 0.6–0.9 W/m²K |
| Whole-window Uw (typical) | 1.2–1.4 W/m²K | 0.8–0.9 W/m²K |
| Acoustic Rw (standard) | 30–32 dB | 36–38 dB |
| Acoustic Rw (laminated) | 38–40 dB | 42–44 dB |
| Weight per m² | ~22 kg | ~33 kg |
| Solar gain (G-value) | 0.50–0.62 | 0.40–0.55 |
| Inner-pane temp (winter, 0°C out) | ~14°C | ~18°C |
| Building Regs Part L compliance | Yes (Uw ≤ 1.4) | Yes (well under) |
Cost premium — London Q2 2026
Indicative London fitted prices showing the triple-glazing uplift on common Apex Glazing systems. Based on a single 1.2m × 1.2m casement opening.
| System | Double | Triple | Uplift |
|---|---|---|---|
| uPVC casement (mid-range) | £700 | £900 | +29% |
| Cortizo Cor 60 aluminium | £1,100 | £1,400 | +27% |
| Cortizo Cor 70 aluminium | £1,400 | £1,750 | +25% |
| Schüco AWS 70.HI | £1,650 | £2,050 | +24% |
| Schüco AWS 90.SI+ (Passivhaus) | Triple only | £2,800 | — |
| Cortizo Cor 4700 (Passivhaus) | Triple only | £2,400 | — |
When triple is worth it
If any of these apply to your project, the third pane earns its keep. Several apply to most Passivhaus and near-Passivhaus retrofits across London's eco-renovation belt (Hackney, Walthamstow, Brixton, parts of Wimbledon).
| Scenario | Why triple wins |
|---|---|
| Passivhaus or near-Passivhaus retrofit | Required by certification (Uw ≤ 0.8 W/m²K). Non-negotiable. |
| North-facing rooms with no solar gain | Lower G-value penalty doesn't matter; lower U-value matters a lot. |
| Properties on major roads (A4, A205, A406, North Circular) | Acoustic upgrade from 32 dB to 42–44 dB Rw is genuinely audible. |
| Properties under flight paths (Heathrow approach) | Combined with laminated outer pane, transforms night-time noise. |
| Large picture windows (over 2m × 2m) | Single largest source of heat loss in the building envelope. |
| North-facing kitchen with consistent condensation | Inner-pane temp rises from ~14°C to ~18°C, eliminating mould risk. |
| Heated to 21°C+ year-round (elderly residents, infants) | Indoor-outdoor delta is large; triple glazing reduces standing-near-window draught. |
| New-build EPC A target | Whole-house energy modelling typically requires triple to hit A. |
When double is enough
For a much larger share of London projects, modern double glazing with argon fill, soft-coat low-E and warm-edge spacers does the job. Don't let upselling pressure you into spec you don't need.
| Scenario | Why double is enough |
|---|---|
| Standard semi-detached upgrade from old double glazing | Modern double (Uw 1.2) is already 40% better than 2005-spec double (Uw 2.0). |
| South-facing or south-east rooms | Solar gain offsets thermal loss. Triple's lower G-value can hurt overall. |
| Quiet residential street, no major traffic | Acoustic upgrade is inaudible. Spend on glass area instead. |
| Decent existing thermal envelope (cavity-insulated walls, loft insulation) | Windows are no longer the weakest link; spending elsewhere wins. |
| Budget-led renovation | Modern double + insulation top-up + draught-proofing beats triple-only. |
| Conservation area heritage frames | Heritage frames often can't accept the 36–44mm cavity triple needs. |
| Buy-to-let or short-hold investment property | Payback period exceeds typical hold. Building Regs compliance is sufficient. |
The frame matters as much as the glass
A triple-glazed unit in a thermally-leaky frame underperforms a double-glazed unit in a Passivhaus-rated frame. When upgrading glass, upgrade the frame in lockstep — don't fit triple glazing into a 1990s aluminium frame and expect Passivhaus numbers.
| Pairing | Whole-window Uw | Verdict |
|---|---|---|
| Old uPVC frame + new triple glazing | ~1.6 W/m²K | Wasted spend on glass |
| Modern uPVC + double glazing (argon) | ~1.3 W/m²K | Building Regs compliant |
| Modern uPVC + triple glazing | ~0.95 W/m²K | Approaching near-Passivhaus |
| Cortizo Cor 70 + double glazing | ~1.2 W/m²K | Building Regs compliant |
| Cortizo Cor 70 + triple glazing | ~0.95 W/m²K | Near-Passivhaus |
| Schüco AWS 90.SI+ + triple glazing | ~0.79 W/m²K | Certified Passivhaus |
| Cortizo Cor 4700 + triple glazing | ~0.8 W/m²K | Certified Passivhaus |
Frequently asked
Is triple glazing worth it in London?
For most standard London semi-detached and terrace properties, no — modern double glazing (Ug 1.0–1.2 W/m²K) already meets Building Regs and the payback on triple glazing is typically 8–12 years. Triple glazing is worth it for: Passivhaus or near-Passivhaus retrofits, north-facing rooms with no solar gain, properties on major roads or under flight paths (acoustic upgrade), and large picture windows where the extra thermal mass justifies cost. For everything else, premium double glazing with argon fill and warm-edge spacers gets you 90% of the benefit at 70% of the cost.
What is the U-value of double vs triple glazing?
Modern double glazing (4-16-4 mm with argon fill, soft-coat low-E) achieves a centre-pane U-value of 1.0–1.2 W/m²K. Triple glazing (4-12-4-12-4 mm with argon or krypton fill, two low-E coatings) achieves 0.6–0.9 W/m²K — roughly 30–45% lower heat loss. Whole-window U-values depend on the frame: a Cortizo Cor 4700 frame with triple glazing hits Uw 0.9 W/m²K; a Schüco AWS 90.SI+ with triple glazing hits Uw 0.79 W/m²K (Passivhaus-certified).
How much extra does triple glazing cost?
In London (Q2 2026), triple glazing typically adds 20–30% to the per-window installed cost. A Cortizo Cor 70 double-glazed casement at £1,400–£2,200 fitted becomes £1,750–£2,800 with triple glazing. The premium covers the third pane, additional spacer bar, krypton or argon fill upgrade, and the heavier hinge and frame engineering needed to support the extra weight.
What's the acoustic difference — double vs triple?
Standard 4-16-4 mm double glazing rates around 30–32 dB Rw. Triple glazing 4-12-4-12-4 mm rates 36–38 dB Rw. Acoustic-spec asymmetric triple (6.4-12-4-12-8.8 mm laminated) reaches 42–44 dB Rw. For acoustic isolation specifically, an asymmetric laminated double glazing (often called 'sound-spec') outperforms standard symmetric triple — sometimes a cheaper double upgrade beats a triple upgrade for noise.
Does triple glazing reduce condensation?
Yes, significantly. With triple glazing the inner pane stays warmer because it's further from the cold outer pane, so internal humidity is much less likely to condense on it. In typical London winter conditions, double-glazed inner panes can sit at 12–15°C; triple-glazed inner panes sit at 17–19°C. Less condensation means less mould risk, especially in bathrooms, kitchens and north-facing bedrooms.
Is triple glazing heavier — does it need stronger frames?
Yes. Triple glazing is roughly 50% heavier than equivalent-size double glazing. Standard aluminium and uPVC casement frames handle it fine up to about 1.2m × 1.2m. Above that, hinges need upgrading and the system spec changes — Schüco AWS 70.HI handles triple glazing as standard but Cortizo Cor 60 requires reinforced hinges above 1.5m wide. Picture windows and tilt-and-turns above 1.5m × 1.8m typically move to a heavier-duty system like Cor 4700 or AWS 90.
What is the payback time for triple glazing?
For a typical London semi-detached upgrade from old single glazing, triple glazing pays back in 6–9 years against rising energy prices. Going from modern Building-Regs-compliant double glazing to triple glazing pays back in 8–12 years on energy savings alone — the comfort, acoustic and condensation benefits arrive immediately. For Passivhaus retrofits where triple glazing is mandatory, payback isn't really the right framing; it's part of the certification cost.
Can triple glazing fit existing window frames?
Usually no. Triple glazing needs a 36–44mm cavity to accommodate three panes plus two air gaps; standard double-glazing cavities are 24–28mm. Most existing aluminium and uPVC frames don't have enough rebate depth to take a triple-glazed unit, so a triple-glazing upgrade typically means a full window replacement rather than just a glass swap.
Triple glazing or secondary glazing for noise?
For acoustic performance specifically, secondary glazing (a second window installed inside the existing frame, with a 100mm+ air gap) usually beats triple glazing — 45–50 dB Rw is achievable. Secondary glazing also preserves listed and conservation-area frontages where new aluminium isn't permitted. Triple glazing wins on thermal performance and condensation; secondary glazing wins on acoustic and heritage compliance.
