FENSA-registered glazing experts. Made-to-measure sealed units, shipped UK-wide, backed by a 10-year warranty.
Triple-glazed sealed units — Scandinavian-spec thermal performance
U-value 0.8 W/m²K and below. Heat-pump-ready. Passive House territory. Triple-glazing isn't just "double-plus-one" — it's a different thermal class. The third pane and second cavity, krypton-filled with two low-E coatings, drop U-values to 0.5-0.8 W/m²K (compared to 1.2 for premium double), make low-temperature heat-pump heating viable without cold-spot draughts at the window line, and noticeably improve room acoustics into the bargain. Pane Relief manufactures 36mm and 44mm krypton-filled triple-glazed sealed units in standard, safety, acoustic, and conservation-slim builds. For the full thermal-strategy context see our triple-glazing technical guide.
Heat-pump install, eco-retrofit, Passive House
Free UK mainland delivery, 10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2), FENSA-registered installer recommendations in your postcode. Phone helpline (08:00-18:00 Mon-Fri) for spec sanity-checks — triple-glazed units are noticeably heavier than double, and frame structural rating matters. Lead time on triple-glazed builds: 10-14 working days.
Configure my unitPassive House, MMC, eco-retrofit contractor
Net 30 trade accounts, tiered volume discount, scheduled site delivery. UKCA-marked, BS EN 1279 compliance, BFRC A+/A++ rating, full Declaration of Performance and SAP/PHPP-ready U-value calculations on request. Bespoke supply agreements for Passive House, retrofit, and MMC contractors.
Trade pricing & bulk ordersWhich triple-glazed build do you need?
Five common triple-glazed sealed-unit configurations. Pick by build depth, gas fill, or application — each links to the relevant product or filter.
36mm argon
4-12-4-12-4 triple-glazed with argon fill and two low-E coatings. U-value around 0.8 W/m²K. Fits modern triple-rated UPVC frames.
44mm krypton
4-18-4-14-4 with krypton gas. U-value 0.5-0.6 W/m²K. The Passive House and Scandi-spec standard. Heat-pump-optimal.
Triple-glazed safety
Toughened or laminated inner pane (BS EN 12150 / 14449) for below-800mm or near-door locations. Standard or low-E build.
Acoustic triple
Asymmetric build with PVB acoustic interlayer on the outer or inner pane. Cuts environmental noise by 42-46 dB Rw.
Slim triple (conservation)
Specialist 28-32mm triple-glazed build for conservation retrofit where U < 1.0 W/m²K is needed in a shallow rebate. Bespoke quote.
Measure twice, order once
Triple-glazed units are significantly heavier (about 28-35 kg/m² vs 20 kg/m² for double). Frame rebate depth and hinge load-rating are real constraints — confirm both before ordering.
The 5-step measure
- Measure the visible glass width at top, middle, and bottom — use the smallest.
- Measure the visible glass height at left, middle, and right — use the smallest.
- Add 6mm to both dimensions for the sealed-unit size.
- Confirm the rebate accepts the unit thickness. 36mm and 44mm are very different — measure the rebate slot edge-on with vernier callipers. If your frame was built for 24mm or 28mm double-glazing, it won't accept triple.
- Check the frame manufacturer's hinge load-rating. Standard UPVC casement hinges are typically rated to 35-40 kg per sash — triple-glazed units in larger sashes can exceed that. Replace hinges if needed.
Pricing transparency
Prices on this collection are "From £X" — the smallest 36mm argon-filled triple-glazed unit at base spec. Krypton fill, A+/A++ coatings, safety (toughened or laminated), acoustic interlayers, conservation slim-profile triple, and oversized panels are priced live in the configurator.
See our triple-glazing technical guide for U-value comparison, payback maths, and frame-compatibility detail.
Triple glazing — common questions answered
Q: Is triple-glazing actually worth it on a typical UK retrofit?
Honest answer: usually not, unless one of three triggers applies. Trigger 1 — you're installing a heat pump: low flow temperatures (40-45 °C) need low-U-value glazing or you'll get cold draughts at the window line. Trigger 2 — Passive House or near-Passive build standard: the entire envelope spec is integrated and triple is non-negotiable. Trigger 3 — noisy site: triple-glazed acoustic builds outperform double significantly on environmental noise. For a standard gas-boiler-heated UK semi with cavity insulation, premium double (U-value 1.0-1.2) is usually the better economic call.
Q: What U-value should I expect from triple-glazing?
Range is 0.5 to 0.8 W/m²K depending on build. A 36mm argon-filled triple with two soft-coat low-E layers hits around 0.8. A 44mm krypton-filled triple with warm-edge spacers and high-performance low-E hits 0.5-0.6. Passive House Institute certification typically requires Uw (whole-window, glass + frame) of 0.8 or below — which needs a 44mm krypton triple in a Passive-certified frame. Full U-value calculations are surfaced in the configurator and supplied for SAP/PHPP submission on request.
Q: Will my existing frames take triple-glazed units?
Only if they were specced for it. Modern UPVC frames built post-2018 for SAP improvements often have 44mm rebates and load-rated hinges suitable for triple-glazed retrofit. Standard 24mm or 28mm frames don't — the rebate physically won't accept a 36mm or 44mm unit. Check the existing sealed-unit thickness with vernier callipers — if it's already 36mm or 44mm, you're fine. If it's 24mm or 28mm, you need new frames (or stay with double-glazing).
Q: Argon or krypton for triple-glazed?
Krypton is typically the right answer for triple, despite the higher cost. Reason: triple-glazed units have two narrower cavities (around 12-14mm each, vs one wider cavity in double), and krypton's higher density gives better convection suppression in narrow cavities. Argon-filled triple gets to U=0.8; krypton-filled gets to U=0.5-0.6 in the same physical envelope. If you're already paying the cost-premium for triple, the krypton uplift is typically a small percentage on top for a meaningful U-value drop.
Q: Is triple-glazing required by current UK Building Regs?
No. Approved Document L (Conservation of fuel and power) requires U-value 1.4 W/m²K or better for replacement glazing in existing dwellings and 1.6 W/m²K for new dwellings (effectively a low-E double-glazed minimum). Triple-glazing is voluntary above-and-beyond — driven by Passive House standards, EPC targeting (A-rated), or heat-pump pairing rather than Building Regs minimum.
Q: Do triple-glazed units block more light or look different?
Marginally — visible light transmittance drops from around 80% (double-glazed with one low-E) to around 70-72% (triple-glazed with two low-E). On a sunny day you won't notice; in a dim north-facing room you might. Modern soft-coat low-E coatings are colour-neutral; older hard-coat coatings could give a slight green-grey tint. Stack a sample over a white sheet before specifying for a large window or feature glazing.
Q: How much heavier is triple-glazed than double, in practice?
About 50-75% heavier per square metre — a 4-16-4 double-glazed unit weighs around 20 kg/m²; a 4-12-4-12-4 triple weighs 28-35 kg/m². For a small bathroom window (under 1m²) it's a non-issue. For a 1.5m×2m casement (3 m²) you're talking 100 kg of glass on the hinges — well above the rating of stock UPVC casement hinges. Heavy-duty hinges or restricted opening angles often become necessary. The configurator flags weight at point of order.
Q: What about acoustic performance — does triple beat double?
Yes — substantially. A standard 4-12-4-12-4 triple-glazed unit gives around 33-36 dB Rw, vs 27-30 dB for symmetric double. A dedicated triple-glazed acoustic build (asymmetric pane thicknesses + PVB acoustic interlayer) reaches 42-46 dB Rw — useful for flightpaths, busy roads, or rail lines. Triple is a meaningful acoustic upgrade if noise is part of the brief — see the acoustic glass guide.
Q: What's the warranty and lead time?
10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2 weathered durability), 5-year on low-E and solar-control coatings. Lead time on triple-glazed builds: 10-14 working days as standard (the extra spacer and second cavity fill takes longer than a comparable double). Acoustic triple and conservation slim-triple builds: 14-21 working days. Free phone sanity-check on spec, frame-compatibility, and weight before ordering: 0117 330 3057.
Related guides, collections, and specifications
Ready to spec a triple-glazed build?
Call the helpline on 0117 330 3057 (08:00-18:00 Mon-Fri), or request a quote. Trade accounts unlock live tier pricing and Net 30 terms.