The default replacement sealed unit for UK homes. A 24mm clear double-glazed unit (4mm clear / 16mm argon-filled cavity / 4mm clear) is the workhorse of British replacement glazing — fitted to the majority of post-2002 PVCu, aluminium, and timber frames, and the unit most failed (misted, blown, condensation-streaked) units in pre-2015 stock are being replaced with. This flagship is built on Pilkington-grade 4mm float glass, a 16mm warm-edge spacer, and a 90% argon fill (factory-tested at 92-95% on initial fill, with 1% per annum loss assumed under BS EN 1279-2). Krypton fill is available as a custom-configure option for slim-cavity variants — for 24mm symmetric units, argon delivers the better cost-per-watt envelope. Technical specification Overall thickness 24mm Build-up 4mm clear float / 16mm cavity / 4mm clear float Gas fill 90% argon (BS EN 1279-3 compliant) Spacer bar Warm-edge composite (Edgetech Super Spacer or equivalent) U-value (centre-pane) 1.4 W/m²K g-value (solar transmittance) 0.72 Light transmittance (LT) ~80% Standards BS EN 1279 (parts 1, 2, 3, 5, 6) Manufactured UK, FENSA-registered supply chain Where this unit is the right call Like-for-like replacement of a failed (misted/blown) post-2002 unit where the frame is sound and the existing rebate accepts a 24mm unit. Internal partitions, porches, and unheated outbuildings where U-value isn't critical and 80% light transmittance matters. Listed-building consents that permit DG where the unit must read as a clear single-pane sightline (24mm clear hides cavity from most viewing angles better than tinted/coated alternatives). Bay windows, dormer cheeks, and small-aperture casements where the 600 × 400 stock size lands without trimming. For applications where U-value is the priority (Building Regs Approved Document L compliance, new-build, A-rated specification), the 28mm Low-E A-Rated variant is the recommended upgrade — same form factor, U-value 1.1 W/m²K, planitherm soft-coat. For acoustic applications (railway lines, flight paths, A-roads), the acoustic glass topical page walks the Rw / dB-reduction math and links to the laminated alternatives. Stock sizes and pricing Five UK-standard stock sizes are listed below. Each is dispatched 5-7 working days from order via our FENSA-registered manufacturing partners. Custom sizes — including shaped, tinted, low-E, toughened, and acoustic variants — are priced via the online glass configurator with the same per-m² rate as the stock units (no custom-size premium). Trade accounts: log in to your account to see your tiered pricing — volume discount applies at 5+ units per order. Certification and standards Every unit ships with a CE/UKCA mark referencing BS EN 1279, a unique IGU stamp inside the cavity (visible at edge), and a Declaration of Performance available on request. Argon fill is tested per BS EN 1279-3 (initial fill ≥85%, annual loss
