FENSA-registered glazing experts. Made-to-measure sealed units, shipped UK-wide, backed by a 10-year warranty.
Ultra energy-efficient triple glazing — U≤0.6 W/m²K with the right stack
This is the premium tier of UK triple-glazing — the units that beat Passivhaus thermal minimums by a clear margin and target whole-window U-values around 0.7 W/m²K when paired with an aluminium-clad timber Passivhaus frame. Getting to U=0.6 or below on the centre-pane requires the full stack: dual low-E coating (sputtered silver on faces 2 and 5), pure krypton fill at ≥95% in both cavities, premium warm-edge spacer (Swisspacer Ultimate or Edgetech TriSeal Premium), and tight build tolerance from manufacture to glazing. Pane Relief manufactures these to PHI component-certified spec — for self-builders chasing the lowest possible heat-loss envelope, for retrofit projects targeting EnerPHit-Plus, and for any glazing budget where running cost dominates capital cost over the building's lifetime.
Beyond-Passivhaus or lifetime-cost driven
If you're building or retrofitting once and aiming to never replace the glass, this is where to spend. The capital uplift over standard A-rated double glazing is significant; the running-cost saving over 30 years more than recovers it. PHPP-ready coating data sheets, 10-year edge-seal warranty, drop-in to most certified Passivhaus frame brands. Free design-stage spec validation on the helpline.
Configure my ultra-tripleEnerPHit-Plus, architect, retrofit coordinator
Net 30 trade accounts, dedicated Passivhaus desk, PHPP component validation against your file before manufacture. BS EN 1279-5 DoP, krypton-fill certificate, coating data sheet, and UKCA/CE mark shipped on request. Bulk-quote portal for large self-build or institutional retrofit programmes. Bespoke shaped and oversize units to 3.2m x 1.6m.
Trade pricing & bulk ordersWhich ultra-efficient triple build do you need?
Five PHI-component-grade builds, plus a true U=0.5 quad option. All exceed Passivhaus minimums.
Ultra 44mm dual-low-E
Sputtered low-E on faces 2 and 5, 18mm x 2 krypton cavities, Swisspacer Ultimate. U=0.6 W/m²K. The collection default.
Premium 48mm triple
20mm x 2 krypton, 4mm low-E both inner faces. U=0.55 W/m²K. For cold-climate or north-facing exposed glazing.
Quad (4-pane) 50mm
Four panes, three krypton cavities, triple low-E coating. U=0.5 W/m²K. Niche product — heavy, expensive, exceptional.
Ultra + laminated safety
Ultra triple with 6.4mm or 8.8mm laminated inner pane for low-level critical-location compliance. U=0.6 maintained.
Ultra + acoustic
Ultra triple with 8.8mm Optiphon/Stadip Silence acoustic outer. U=0.6 W/m²K, Rw 44-48 dB. Urban Passivhaus default.
Standard PHI triple
Just need PHI-spec (U=0.7-0.8)? See the Passive House triple-glazing collection for the standard tier at lower price point.
What gets you below U=0.6 — the engineering details
A short explainer on why every component matters. Standard "triple glazing" without the full stack will only get to about U=0.9-1.0 — not where this collection sits.
The 5 elements of an ultra-low-U triple
- Dual sputtered low-E: soft-coat silver layer on face 2 AND face 5. Total emissivity around 0.025 per face — roughly halves the radiative heat-loss component of the unit.
- Pure krypton fill (≥95%): krypton's thermal conductivity is around 60% of argon's. Pane Relief uses certified pure krypton (not the cheaper krypton-argon blend) with gas-fill certificate on request.
- Cavity width tuning: krypton works best in 12-18mm cavities (gas convection optimum). 36mm overall = 14mm + 14mm; 44mm overall = 18mm + 18mm. Wider isn't always better — convection starts to undo the gas-conductivity gain past 20mm.
- Premium warm-edge spacer: Swisspacer Ultimate or Edgetech Super Spacer TriSeal Premium. Edge psi Ψg around 0.025-0.030 W/mK — best-in-class. Standard aluminium spacer would add 0.10 W/mK and destroy the rating.
- BS EN 1279-3 gas retention: tighter spec than standard CE/UKCA — gas loss <1% per year over 25 years. Critical for maintaining the U-value over the unit's design life.
Pricing & documentation
Prices on this collection are "From £X" at the smallest stock size with U=0.6 W/m²K dual-low-E krypton build. Custom sizes, U=0.55 premium builds, quad units, and acoustic upgrades priced live in the configurator. PHPP-ready data sheet and krypton-fill certificate shipped on request — no charge.
Ultra-efficient triple glazing — common questions answered
Q: Where does U=0.6 actually sit on the energy ladder?
For context: 1990s uncoated DG is around U=2.7-3.0. Modern A-rated DG with low-E argon: U=1.2-1.4. Standard PHI triple: U=0.7-0.8. This collection: U=0.5-0.6. Quad-pane experimental glazing: U=0.4. The thermal practical limit for sealed-unit technology is around U=0.3-0.4 before vacuum or aerogel glazing kicks in. U=0.6 is roughly four to five times better than uncoated DG.
Q: Is the U=0.5 quad-pane unit a real product or a science experiment?
It's a real product — manufactured to order, certified to BS EN 1279, and used in genuine Beyond-Passivhaus and PassivLab projects. It's also heavy (over 40 kg/m²), expensive (typically 2-2.5x the price per m² of a standard 44mm triple), and demands the right frame and installation. For 99% of UK projects the 44mm or 48mm triples are the right call. Quad makes sense for very cold microclimates, extreme passive-cooling-dependent designs, or where running cost over a 50-100 year horizon dominates the brief.
Q: How long does krypton stay in the cavity?
BS EN 1279-3 requires ≤1% gas loss per year — over 25 years that's a maximum 25% degradation in fill concentration. Pane Relief ultra-efficient units are built with high-spec primary and secondary seals (PIB + silicone) and tested in batch to BS EN 1279-3 weathered durability. In practice, modern units typically hold 92-95% of original krypton at 20 years. The U-value drift is small — typically 0.05 W/m²K over the life of the unit.
Q: Will the dual low-E coating make rooms feel dark?
Marginally less light than a single-coat unit. Visible light transmittance on a dual-low-E krypton triple lands around 70-74% — compared to 80% on a standard A-rated DG and 89% on uncoated single. In practice, the eye adapts within seconds and rooms feel only slightly less bright. Spectrally selective coatings preserve colour rendering (CRI >95) so colours look natural — not muddy.
Q: How does this compare to vacuum glazing or aerogel glazing?
Different technologies, different niches. Vacuum glazing (Pilkington Spacia, LandVac) achieves U=0.4-0.7 in just 6-8mm thickness — useful for heritage and listed-building retrofits where frame depth is limited. Higher capital cost, narrower size range, edge-seal failure mode is more brittle. Aerogel glazing is still semi-experimental — translucent rather than transparent. For new-build and standard EnerPHit, the dual-low-E krypton triple in this collection is the mainstream choice.
Q: Capital uplift vs A-rated DG — is it worth it?
For new-build aiming at Passivhaus or EnerPHit certification: yes, you can't get there without it. For straight retrofit driven by capital-cost minimisation: probably not — A-rated low-E argon DG already gives you 60% of the heat-loss reduction at 25-30% of the cost. The break-even depends on gas/electricity price trajectory and how long you'll own the building. Rough rule: if you'll own the building 20+ years and grid carbon costs continue trending up, ultra-triple pays back. If you'll move inside 10 years, A-rated DG is the rational choice.
Q: How heavy are these units?
A 44mm dual-low-E krypton triple at 4mm pane thickness weighs about 30-32 kg/m². A 48mm premium build: 33-36 kg/m². The U=0.5 quad unit: 40-44 kg/m². Frame weight ratings, hinge capacity, and installer handling guidance all need to be checked against these — most Passivhaus aluminium-clad timber frames are rated for 50+ kg/m² without issue, but legacy timber frames are usually not. Confirm before ordering.
Q: What's the longest lead time I should expect?
Ultra 44mm dual-low-E krypton: 14-21 working days. Premium 48mm: 21-28 working days. Quad U=0.5 unit: 28-42 working days (manufactured against firm order only). Acoustic ultra builds: 21-28 working days. Plan accordingly — these are not stock items, every unit is built to order against the certified krypton supply chain.
Related guides and specifications
Need spec advice for an ultra-low-U build?
Call the Passivhaus desk on 0117 330 3057 (08:00-18:00 Mon-Fri), or request a quote. Trade and Passivhaus consultancy accounts available.