{"product_id":"triple-glazed-conservation-krypton-slim-cavity-unit","title":"Triple Glazed Conservation Unit (Krypton, Slim Cavity)","description":"\n\u003cp class=\"pr-flagship__lede\"\u003e\u003cstrong\u003eTriple-glazed thermal performance in a conservation-friendly slim envelope\u003c\/strong\u003e. A 26mm triple-glazed sealed unit (4mm clear \/ 8mm krypton \/ 4mm clear with soft-coat low-E \/ 8mm krypton \/ 4mm clear with soft-coat low-E) delivers a centre-pane U-value of 0.9 W\/m²K in an overall depth that fits many heritage timber sash rebates where the standard 36mm triple cannot.\u003c\/p\u003e\n\n\u003cp\u003eThis is a niche product engineered for a specific intersection: heritage and conservation apertures where the conservation officer accepts slim double-glazing in principle, but the building physics ask for triple-pane performance — typically Passivhaus-EnerPHit retrofits in Grade II listed Victorian and Edwardian properties, or deep-retrofit projects in conservation-area townhouses where heritage joinery is being conserved alongside fabric-first energy upgrades.\u003c\/p\u003e\n\n\u003ch2\u003eWhy krypton, and why 8mm cavities\u003c\/h2\u003e\n\u003cp\u003eCavity gas performance is a function of cavity depth. In a 16mm cavity (standard 24mm DG), argon is optimal — krypton offers no further U-value benefit and costs five times more. Below 10mm, argon's convective performance degrades and krypton becomes the better insulator. At 8mm cavities (this unit), krypton is the only fill that delivers meaningful insulation: argon at 8mm gives ~1.4 W\/m²K centre-pane in a triple stack; krypton drops that to ~0.9.\u003c\/p\u003e\n\n\u003cp\u003eTwo 8mm krypton cavities at 26mm total overall is a precise engineering trade. Smaller cavities sacrifice convective insulation; larger cavities push the overall thickness beyond the conservation-aperture limit. 8mm is the cavity depth that the krypton-vs-argon curve crosses over and where slim-cavity edge-seal manufacturing yield is still acceptable.\u003c\/p\u003e\n\n\u003ch2\u003eTechnical specification\u003c\/h2\u003e\n\u003ctable class=\"pr-spec-table\"\u003e\n  \u003ctr\u003e\n\u003cth\u003eOverall thickness\u003c\/th\u003e\n\u003ctd\u003e26mm (nominal — tolerance ±0.5mm)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eBuild-up\u003c\/th\u003e\n\u003ctd\u003e4mm clear \/ 8mm krypton \/ 4mm clear (Planitherm face 3) \/ 8mm krypton \/ 4mm clear (Planitherm face 5)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eCavities\u003c\/th\u003e\n\u003ctd\u003e2 × 8mm krypton-filled (BS EN 1279-3 verified ≥90%)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eSpacer bars\u003c\/th\u003e\n\u003ctd\u003e2 × warm-edge slim composite (typ. 6mm)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eU-value (centre-pane)\u003c\/th\u003e\n\u003ctd\u003e0.9 W\/m²K\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eU-value (whole window, heritage timber sash)\u003c\/th\u003e\n\u003ctd\u003e1.4-1.6 W\/m²K depending on frame condition\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eg-value\u003c\/th\u003e\n\u003ctd\u003e0.52\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eLight transmittance\u003c\/th\u003e\n\u003ctd\u003e~71%\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eSightline \/ cavity-edge appearance\u003c\/th\u003e\n\u003ctd\u003e~22-24mm visible — wider than slim DG, narrower than standard triple\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eWeight\u003c\/th\u003e\n\u003ctd\u003e~30 kg\/m² — confirm sash-cord \/ pulley load before specifying for original sashes\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eStandards\u003c\/th\u003e\n\u003ctd\u003eBS EN 1279 (parts 1-6), BS EN 673, Historic England slim-DG guidance compatible (case-by-case)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eWhere this unit is the right call\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eListed-building EnerPHit retrofits\u003c\/strong\u003e — Passivhaus-Institut retrofit standard wants whole-window U ≤ 1.05 W\/m²K. This unit gets close in a heritage sash; the alternative (full sash replacement to modern frame) is rarely consented.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eConservation-area deep retrofit\u003c\/strong\u003e — particularly Article 4 direction areas in inner London, Bath, Edinburgh, Brighton, where sightlines are protected but EPC targets force fabric upgrade.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eEdwardian and late-Victorian timber sashes\u003c\/strong\u003e with original glazing rebates 24-28mm deep — too shallow for standard triple, too valuable thermally for slim DG to suffice.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eListed-building heat-pump retrofits\u003c\/strong\u003e — ASHPs work best at low flow temperatures (35-45°C), which requires lower fabric heat loss than slim DG alone provides.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eProperty-specific officer-approved alternatives to secondary glazing\u003c\/strong\u003e — where the conservation officer has rejected secondary glazing on sightline or maintenance-access grounds.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eFor shallower 14mm conservation apertures, the \u003ca href=\"\/products\/14mm-slim-krypton-conservation-double-glazed-unit\"\u003e\u003cstrong\u003e14mm Slim Krypton Double Glazed Unit (Conservation) flagship\u003c\/strong\u003e\u003c\/a\u003e is the appropriate spec. For modern apertures where 36mm triple fits without conservation constraints, the \u003ca href=\"\/products\/36mm-standard-triple-glazed-unit\"\u003e\u003cstrong\u003e36mm Standard Triple Glazed Unit\u003c\/strong\u003e\u003c\/a\u003e is dramatically cheaper. This 26mm slim-triple is specifically for the heritage-aperture-plus-deep-retrofit intersection.\u003c\/p\u003e\n\n\u003ch2\u003eStock sizes and pricing\u003c\/h2\u003e\n\u003cp\u003eFive UK-standard stock sizes below — all sized to fit common heritage sash apertures. Dispatch 21-28 working days (slim-cavity krypton-filled triple is the most specialist build in the range — manufacturing yield is lower, lead time longer). Custom sizes — including narrow-tall sash proportions (3:1 height-to-width), arched-top apertures, and bespoke sightline matching for officer approvals — are priced via the \u003ca href=\"\/pages\/configure\"\u003e\u003cstrong\u003eonline glass configurator\u003c\/strong\u003e\u003c\/a\u003e.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eNote on listed-building consent:\u003c\/strong\u003e conservation officer acceptance of slim triple is more property-specific than acceptance of slim double. The case is strongest when (a) the existing glazing has failed beyond viable repair, (b) the slim-triple sightline can be matched within 3-4mm of the original, and (c) the property's energy performance is a stated planning consideration (e.g., MEES enforcement risk for a listed-building landlord). Pre-submission consultation with the conservation officer is essential. We supply a technical evidence pack on request.\u003c\/p\u003e\n\n\u003ch2\u003eCertification and standards\u003c\/h2\u003e\n\u003cp\u003eUKCA-marked, BS EN 1279 compliant across all six parts. Krypton gas fills (both cavities) verified per BS EN 1279-3 at initial fill ≥90% with annual loss \u0026lt;1% under EN-1279-2 accelerated weathering. Slim-cavity construction adds an additional hydrostatic-pressure-cycle stamp per batch. PHI-component certification is available for EnerPHit projects — request at order.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently asked questions\u003c\/h2\u003e\n\u003ch3\u003eHow is this different from the 14mm slim-DG conservation unit?\u003c\/h3\u003e\n\u003cp\u003eDifferent aperture, different physics. The 14mm slim DG fits original Georgian \/ early-Victorian sashes (8-14mm rebates); the 26mm slim triple needs at least a 28mm rebate, which is typical of Edwardian and very-late-Victorian timber sashes, or sashes that have been previously rebated-out. The slim triple is a deeper thermal upgrade — U=0.9 vs U=1.6 — but at significantly higher cost and longer lead time.\u003c\/p\u003e\n\n\u003ch3\u003eWill my sash take a 30 kg\/m² unit?\u003c\/h3\u003e\n\u003cp\u003eSash-cord and balance-pulley systems are the limiting factor on original timber sashes. A 600 × 1200 mm unit at this weight is ~22 kg per pane — within most original sash balance-weight specifications. A 1500 × 1200 mm unit at 54 kg often exceeds original counterweight capacity and may need a sash-spring conversion or steel-balance retrofit. Confirm with your joiner before ordering.\u003c\/p\u003e\n\n\u003ch3\u003eConservation officer evidence — what do I need?\u003c\/h3\u003e\n\u003cp\u003eTypically: (1) photographs of the existing glazing showing failure mode, (2) elevations showing the slim-triple sightline overlaid on the original, (3) BS EN 1279 Declaration of Performance, (4) krypton fill certificate, (5) a SAP \/ RdSAP report showing the projected EPC improvement. We supply items 3-4 directly; items 1-2-5 are the homeowner \/ architect's responsibility. Pre-submission consultation is recommended.\u003c\/p\u003e\n\n\u003ch3\u003eWhat's the cost premium vs slim DG?\u003c\/h3\u003e\n\u003cp\u003eApproximately 60-80% more, depending on size. Triple-pane krypton-filled construction at slim cavities is the most specialist build in mainstream IGU manufacturing — yields are lower, edge-seal tolerances tighter, and only a handful of UK manufacturers can produce this spec at scale. For most heritage applications, slim DG remains the cost-optimal choice; this unit is for projects where deep-retrofit thermals are the explicit goal.\u003c\/p\u003e\n\n\u003ch3\u003eKrypton retention — 25-year outlook?\u003c\/h3\u003e\n\u003cp\u003eIndustry standard is \u0026lt;1% per year under EN-1279-2 accelerated weathering, in both cavities independently. Over 25 years that's ~22% loss per cavity — at 78% krypton + 22% air, centre-pane U-value rises from 0.9 to ~1.05 W\/m²K. Edge-seal failure typically arrives first (15-25 years) and is the dominant failure mode rather than gas diffusion.\u003c\/p\u003e\n\n\u003ch3\u003eCan it be heat-soaked \/ toughened?\u003c\/h3\u003e\n\u003cp\u003eOuter faces can be toughened on order — adds Class 1(C)1 impact rating if needed for critical-location heritage glazing (e.g., low-level sashes within 800mm of floor). The inner laminated pane option (for overhead heritage glazing, rare but specified for some chapel\/ecclesiastical work) is also configurable.\u003c\/p\u003e\n\n\u003ch3\u003eWarranty?\u003c\/h3\u003e\n\u003cp\u003e10 years on edge-seal integrity (BS EN 1279-2). 10 years on krypton retention to ≥80% of initial fill, per cavity. 5 years on each Planitherm coating. Heritage installations are warranted on the same terms — installation must be by a competent joiner familiar with sash counterbalance systems and conservation-grade glazing methods.\u003c\/p\u003e\n","brand":"Pane Relief","offers":[{"title":"600 × 400 mm","offer_id":61853953818954,"sku":"TG-CONSKR-600x400","price":54.0,"currency_code":"GBP","in_stock":true},{"title":"800 × 600 mm","offer_id":61853953851722,"sku":"TG-CONSKR-800x600","price":108.0,"currency_code":"GBP","in_stock":true},{"title":"1000 × 800 mm","offer_id":61853953884490,"sku":"TG-CONSKR-1000x800","price":179.0,"currency_code":"GBP","in_stock":true},{"title":"1200 × 1000 mm","offer_id":61853953917258,"sku":"TG-CONSKR-1200x1000","price":268.0,"currency_code":"GBP","in_stock":true},{"title":"1500 × 1200 mm","offer_id":61853953950026,"sku":"TG-CONSKR-1500x1200","price":402.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0895\/3515\/2458\/files\/triple-glazed-insulated-glass-unit-igu-cutaway_5ee617f9-b89f-46fb-bb72-b185f90de41d.webp?v=1779018548","url":"https:\/\/panerelief.co.uk\/products\/triple-glazed-conservation-krypton-slim-cavity-unit","provider":"Pane Relief","version":"1.0","type":"link"}