The Passivhaus spec — without the bespoke German lead time. A 44mm premium triple-glazed unit (4mm / 16mm krypton + soft-coat low-E / 4mm / 16mm krypton + soft-coat low-E / 4mm) delivers a centre-pane U-value of 0.5 W/m²K and a whole-window U-value of 0.7-0.8 W/m²K in a thermally-broken frame — meeting the Passivhaus Institut's strict 0.8 W/m²K window requirement for cool-temperate climates. This is the spec the Scandinavian and German new-build market has used as a baseline for two decades. In the UK, it appears in Passivhaus retrofits (EnerPHit), Future Homes Standard pilot projects, and any deep-retrofit where fabric heat-loss is being driven below 15 kWh/m²·yr. It is the most thermally-efficient mainstream IGU available, and the spec heat-pump-led retrofits depend on to keep flow temperatures at 35-45°C. Why both krypton fills AND dual low-E coatings Each thermal layer compounds. Krypton at 16mm in this unit's wider cavity gives ~10% additional benefit over argon (the cavity is just shallow enough that krypton still outperforms). Soft-coat low-E on faces 3 and 5 — the inner surfaces of each cavity — reflects long-wave radiant heat back into the warm side of each cavity. The dual-coating strategy means each cavity does roughly half the work, instead of single-coating loading all the thermal performance onto one face. Technical specification Overall thickness 44mm Build-up 4mm clear / 16mm krypton / 4mm clear (Planitherm face 3) / 16mm krypton / 4mm clear (Planitherm face 5) Cavities 2 × 16mm krypton-filled (BS EN 1279-3 verified ≥90%) Spacer bars 2 × warm-edge composite, black low-conductivity U-value (centre-pane) 0.5 W/m²K U-value (whole window in thermally-broken alu/timber frame) 0.7-0.8 W/m²K g-value 0.50 (slightly lower than standard triple — dual coating trade) Light transmittance ~70% BFRC Window Energy Rating A++ (when fitted in a compliant Passivhaus frame) Weight ~30 kg/m² — confirm hinge / sash rating Standards BS EN 1279, BS EN 673, BS EN 410, PHI window certification compatible Where this unit is the right call Passivhaus and EnerPHit projects — Passivhaus Institut whole-window requirement is ≤ 0.8 W/m²K for cool-temperate climates. This unit delivers it in a standard frame. Heat-pump retrofits — ASHPs operate most efficiently at low flow temperatures (35-45°C). Premium triple cuts fabric heat loss enough that an ASHP can hold setpoint without bumping flow temperature into the high-COP penalty zone. Future Homes Standard pilot builds — the 2025+ FHS draft envelope targets whole-window U ≤ 0.8 W/m²K. This spec is the cleanest path. EPC band A targets — for landlords planning ahead of the proposed 2030 MEES B (or future C-ratchet), premium triple is the glazing spec that consistently scores band-A. North-facing principal rooms in deep-retrofit projects where every kWh of fabric heat loss matters and the install budget can absorb the premium. The whole-window thermal math, BFRC vs PHI certification, and a side-by-side payback analysis against A-rated double is on the triple glazing topical page. For Building Regs Approved Document L compliance only (not Passivhaus), the lower-cost 36mm Standard Triple Glazed Unit is the practical choice. Stock sizes and pricing Five UK-standard stock sizes below. Dispatch 10-14 working days (premium krypton + dual coating extends lead time vs standard triple). Custom sizes via the configurator — including Passivhaus-certified frames, oversized panes (>1500mm), and asymmetric panes for combined thermal-plus-acoustic stacks. Frame load note: at ~30 kg/m² this unit is materially heavier than double glazing. Hinge capacity, frame reinforcement, and sash-balance specifications need to be checked. For a 1500 × 1200 unit, that's roughly 54 kg — outside the capacity of many budget PVCu profiles. Confirm with your frame supplier before specifying. Certification and standards UKCA-marked, BS EN 1279 compliant. PHI-certified component manufacturers carry a Passivhaus stamp — request this batch stamp at order for Passivhaus project documentation. The dual Planitherm coatings carry Saint-Gobain's batch certification. Krypton retention is warranted to ≥80% of initial fill at 10 years. Frequently asked questions Is the premium over standard triple worth it? Depends on the energy strategy. For a heat-pump-led deep retrofit driving toward 15 kWh/m²·yr fabric demand: yes — the 0.3 W/m²K centre-pane reduction integrates over a heating season into measurable kWh savings. For Building Regs replacement on a 1980s extension: probably not — the standard triple does the regs job at ~70% of the cost. Will my frame take this unit? Modern 70-90mm thermally-broken aluminium and timber-aluminium composite frames are designed for 44-48mm units. Older 60mm PVCu and most 1990s aluminium will not accept it — you'd be replacing the whole window assembly, not just reglazing. Send a frame profile photo to our contact form for compatibility advice before ordering. Why is g-value lower than standard triple? Two soft-coat low-E layers vs one in a standard triple. Each coating reflects some short-wave solar plus most long-wave radiant. Two coatings reflect more solar — that's the price of the U-value improvement. For south-facing principal rooms in colder climates, the passive solar loss is real and worth modelling against the U-value win. Krypton retention over 25 years? Industry standard is
