{"product_id":"28mm-triple-glazed-slim-rebate-retrofit-unit","title":"28mm Triple Glazed Unit (Slim Rebate Retrofit)","description":"\n\u003cp class=\"pr-flagship__lede\"\u003e\u003cstrong\u003eTriple-glazing performance in a 28mm-rebate frame\u003c\/strong\u003e. A 28mm triple-glazed sealed unit (3mm clear \/ 8mm argon \/ 3mm clear with planitherm soft-coat \/ 8mm argon \/ 3mm clear) gives the thermal envelope of a triple-pane build without forcing a frame swap. The 28mm overall thickness drops straight into the same rebate that originally housed a 28mm double-glazed unit — the most common UK replacement scenario for early-2000s PVCu, aluminium, and timber casements.\u003c\/p\u003e\n\n\u003cp\u003eMost homeowners assume triple glazing requires a 36mm or 44mm rebate (the standard for new-build triple), which means tearing out the frame. The slim-rebate triple build solves that constraint: thinner panes (3mm not 4mm), narrower cavities (8mm not 16-20mm), and argon-not-krypton keeps the price below specialist territory. The trade-off is U-value: ~1.0 W\/m²K centre-pane vs ~0.7 W\/m²K for a full-fat 44mm krypton triple. Still meaningfully better than any 28mm double-glazed unit.\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\u003e28mm\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eBuild-up\u003c\/th\u003e\n\u003ctd\u003e3mm clear \/ 8mm argon \/ 3mm clear with Planitherm Total+ soft-coat (face 3) \/ 8mm argon \/ 3mm clear with Planitherm Total+ soft-coat (face 5)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eGas fill\u003c\/th\u003e\n\u003ctd\u003e90% argon, both cavities (BS EN 1279-3)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eSpacer bar\u003c\/th\u003e\n\u003ctd\u003eWarm-edge composite, black — twin spacers\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eU-value (centre-pane)\u003c\/th\u003e\n\u003ctd\u003e1.0 W\/m²K\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eU-value (whole window, PVCu frame)\u003c\/th\u003e\n\u003ctd\u003e~1.3 W\/m²K\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eg-value\u003c\/th\u003e\n\u003ctd\u003e0.50\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eLight transmittance\u003c\/th\u003e\n\u003ctd\u003e~71% (twin Low-E coatings reduce LT vs single-coat)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eBFRC Window Energy Rating\u003c\/th\u003e\n\u003ctd\u003eA (in compliant frame)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eSound reduction (Rw)\u003c\/th\u003e\n\u003ctd\u003e~33 dB (twin cavities give modest acoustic uplift over double)\u003c\/td\u003e\n\u003c\/tr\u003e\n  \u003ctr\u003e\n\u003cth\u003eStandards\u003c\/th\u003e\n\u003ctd\u003eBS EN 1279, BS EN 673 (U-value), BS EN 410 (light\/solar), BS EN 12758 (acoustic)\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\u003e2002-2015 PVCu casements with 28mm-rebated sashes\u003c\/strong\u003e — the dominant UK replacement-window vintage. The rebate accepts 28mm overall; full-fat triple won't fit without re-rebating or full frame replacement.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAluminium curtain-walling and aluminium casements with 28mm rebates\u003c\/strong\u003e — commercial \/ shop-front retrofits where frame replacement is uneconomic but Building Regs Part L compliance is required.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eListed buildings with conservation-officer-mandated 28mm rebate retention\u003c\/strong\u003e — where the original sash sightline must be preserved and Krypton-slim alternatives don't deliver enough thermal performance.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eApproved Document L1B replacement compliance\u003c\/strong\u003e where a 28mm Low-E double won't quite hit the target — the triple build buys 0.1-0.2 W\/m²K headroom for borderline cases.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eProperty re-mortgage \/ EPC upgrade prep\u003c\/strong\u003e — A-rated WER on a 28mm-rebate frame lifts the building's energy band without the disruption of full frame replacement.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eFor frames rebated for 32mm units, the \u003ca href=\"\/products\/32mm-triple-glazed-mid-thickness-retrofit-unit\"\u003e\u003cstrong\u003e32mm Triple Glazed Mid-Thickness Retrofit\u003c\/strong\u003e\u003c\/a\u003e sits in the middle of the cavity-depth \/ cost \/ U-value tradeoff. For new-build or full frame replacement projects, the \u003ca href=\"\/products\/36mm-standard-triple-glazed-unit\"\u003e\u003cstrong\u003e36mm Standard Triple Glazed Unit\u003c\/strong\u003e\u003c\/a\u003e and \u003ca href=\"\/products\/44mm-premium-triple-glazed-krypton-low-e-unit\"\u003e\u003cstrong\u003e44mm Premium Triple Krypton\u003c\/strong\u003e\u003c\/a\u003e options give better thermals. The full \u003ca href=\"\/pages\/triple-glazing\"\u003e\u003cstrong\u003etriple-glazing topical page\u003c\/strong\u003e\u003c\/a\u003e covers the cavity-depth decision tree.\u003c\/p\u003e\n\n\u003ch2\u003eStock sizes and pricing\u003c\/h2\u003e\n\u003cp\u003eFive UK-standard stock sizes are listed below. Custom rectangular sizes and shaped variants are priced via the \u003ca href=\"\/pages\/configure\"\u003e\u003cstrong\u003eonline glass configurator\u003c\/strong\u003e\u003c\/a\u003e. Dispatch is 10-14 working days from order (twin sealed-unit assembly + dual low-E coatings add 3-5 days vs standard double).\u003c\/p\u003e\n\n\u003ch2\u003eCertification and standards\u003c\/h2\u003e\n\u003cp\u003eEvery unit ships with: UKCA mark, BS EN 1279 Declaration of Performance, dual-cavity argon-fill certificate, low-E coating identification on both surfaces, and a Letter of Conformance referencing BS EN 673 (U-value), BS EN 410 (light\/solar), and BS EN 12758 (acoustic). For Approved Document L sign-off, the supplied U-value certificate is sufficient evidence.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently asked questions\u003c\/h2\u003e\n\u003ch3\u003eWill this really fit a 28mm rebate?\u003c\/h3\u003e\n\u003cp\u003eYes — that's the entire design intent. The overall thickness is 28mm ± 0.5mm (BS EN 1279-1 tolerance). Confirm your existing unit reads 28mm overall with calipers at the rebate after carefully removing the inner bead. If your existing unit is 24mm overall, the rebate may be 24mm — in which case the 28mm slim-rebate triple needs a 4mm rebate deepening (achievable via beading swap in PVCu, harder in aluminium).\u003c\/p\u003e\n\n\u003ch3\u003eWhy not just go full 36mm triple?\u003c\/h3\u003e\n\u003cp\u003eA 36mm triple requires a 36mm rebate. Most pre-2015 UK replacement frames are rebated for 28mm. Retrofitting full-fat triple means tearing out the frame — typically £400-600 per opening for PVCu replacement, plus disruption. The 28mm slim-rebate build buys 80-85% of the thermal performance for 5-10% of the disruption cost.\u003c\/p\u003e\n\n\u003ch3\u003eHow much better than a 28mm Low-E double?\u003c\/h3\u003e\n\u003cp\u003eU-value: 28mm triple = 1.0 W\/m²K centre-pane vs 28mm Low-E double = 1.1 W\/m²K. Marginal on paper, but the triple delivers the third pane's radiant-heat-reflection more reliably across temperature differentials. In a -5°C external \/ +20°C internal test, the triple's internal pane surface temperature is ~17°C vs the double's ~14°C — meaningful for condensation-prone bedrooms and bathrooms.\u003c\/p\u003e\n\n\u003ch3\u003eAcoustic performance?\u003c\/h3\u003e\n\u003cp\u003eRw ~33 dB — modest 3 dB uplift over a 28mm Low-E double (Rw ~30 dB). The twin cavity helps with low-frequency rumble (HGVs, washing machines through walls), but for serious acoustic problems the \u003ca href=\"\/products\/triple-glazed-acoustic-unit-44db-rw\"\u003eTriple Glazed Acoustic Unit (44 dB Rw)\u003c\/a\u003e with PVB interlayer is the right call. See \u003ca href=\"\/pages\/acoustic-glass\"\u003eacoustic glass topical page\u003c\/a\u003e.\u003c\/p\u003e\n\n\u003ch3\u003eLead time?\u003c\/h3\u003e\n\u003cp\u003e10-14 working days. The twin sealed-unit assembly adds 3-5 days over a standard double, and the dual low-E coating runs are scheduled in batches by the float-glass coating supplier. Shaped or non-stock sizes add another 5-7 days.\u003c\/p\u003e\n\n\u003ch3\u003eWarranty?\u003c\/h3\u003e\n\u003cp\u003e10 years on edge-seal integrity (BS EN 1279-2 accelerated-weathering tested). 10 years on argon retention to ≥80% of initial fill across both cavities. 10 years on low-E coating integrity. Transit damage covered 14 days from delivery.\u003c\/p\u003e\n\n\u003ch3\u003eCan it be specified shaped (arched, raked)?\u003c\/h3\u003e\n\u003cp\u003eYes — see the \u003ca href=\"\/products\/shaped-triple-glazed-unit-arched-raked-circular\"\u003eShaped Triple Glazed Unit (Custom Cut)\u003c\/a\u003e flagship for the bespoke template flow. Shaped triple in a 28mm rebate is uncommon but achievable on simple geometric cuts (arched-top, raked-top); circular and elliptical inserts at 28mm overall are at the edge of manufacturing yield.\u003c\/p\u003e\n","brand":"Pane Relief","offers":[{"title":"600 × 400 mm","offer_id":61855201165642,"sku":"TG28-SLIMRB-600x400","price":45.0,"currency_code":"GBP","in_stock":true},{"title":"800 × 600 mm","offer_id":61855201198410,"sku":"TG28-SLIMRB-800x600","price":88.0,"currency_code":"GBP","in_stock":true},{"title":"1000 × 800 mm","offer_id":61855201231178,"sku":"TG28-SLIMRB-1000x800","price":147.0,"currency_code":"GBP","in_stock":true},{"title":"1200 × 1000 mm","offer_id":61855201263946,"sku":"TG28-SLIMRB-1200x1000","price":220.0,"currency_code":"GBP","in_stock":true},{"title":"1500 × 1200 mm","offer_id":61855201296714,"sku":"TG28-SLIMRB-1500x1200","price":330.0,"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_ea9c6496-98e7-4ec7-b71f-b022fe747835.webp?v=1779039918","url":"https:\/\/panerelief.co.uk\/products\/28mm-triple-glazed-slim-rebate-retrofit-unit","provider":"Pane Relief","version":"1.0","type":"link"}