Frequently Asked Questions

CSU sealed units are air-filled as standard; argon fill (minimum 90% concentration) is an optional upgrade. Argon has 34% lower thermal conductivity than air, improving insulation by ~15%. Krypton available on request for slim-cavity applications. See our argon gas guide for the full comparison.

We recommend Swisspacer Ultimate (conductivity 0.19 W/mK, Psi 0.030) or Super Spacer TriSeal (0.17 W/mK, Psi 0.028). These eliminate edge condensation, improve U-value by 0.1-0.2 W/m²K, and can improve Window Energy Rating by one full band. Available in all widths 6-24mm. Full detail in our warm edge spacer guide. Spacer systems and unit components are sourced mainly from Thermoseal Group and DGS.

Standard line: 3210 × 2500mm. Jumbo line: 6000 × 3210mm — the largest standard sealed unit available in the UK. Maximum size depends on glass type, thickness and total weight. See our jumbo units page or contact us for specific confirmation.

Our standard recommendation is 28mm (4-20-4): 4mm outer pane, 20mm argon-filled cavity, 4mm inner pane with Pilkington Optitherm S3 soft coat Low-E, Swisspacer Ultimate warm edge spacer. Centre-pane U-value: 0.9 W/m²K. This exceeds Building Regulations Part L by 36%. Full range on our standard DGU page.

Pilkington (Optitherm S3, K Glass S, Suncool, Activ, Optiwhite, Optiphon), Saint-Gobain (Planitherm Total+, Ultra N, Cool-Lite, Bioclean, Stadip, Stadip Silence, Diamant, Parsol, Contraflam), Guardian (ClimaGuard Premium2, SunGuard), AGC (iplus, Lacobel T, Stopray, Clearvision). See our full glass types range.

Yes. Our integral blind range covers Venetian, pleated and blackout systems with cord, magnetic-slider, motorised and solar-powered controls — ask our team which system suits your unit sizes.

Toughened is 4-5× stronger and breaks into small granules (safety glass). Laminated stays intact after breakage (post-break barrier). Toughened is required in doors/low-level/bathrooms. Laminated is MANDATORY for overhead glazing, balustrades, walk-on glass and barriers. For maximum safety, use toughened laminated (both benefits).

Yes. E30 to EI60 classifications. Products: Pyroguard (E30/E60), Pilkington Pyrostop (EI30), Pilkington Pyrodur (EW30), SGG Contraflam (EI30-EI60). Fire glass must be installed in tested, approved framing systems and cannot be cut or modified on site. See our fire-rated glass page.

Yes. Any non-rectangular shape: arches, circles, triangles, trapezoids, rakes, pentagons, octagons, radius corners, bespoke. Minimum curve radius 150mm. Provide a full-size template, dimensioned drawing, or DXF/CAD file. 5-7 day lead time (10+ for complex shapes). See our shaped units page.

5-year guarantee against seal failure and internal condensation on all sealed units. 5-year warranty on integral blind systems. 2-year on external blind components.

Internal condensation (between panes) indicates the unit seal has failed — moisture has entered the cavity, and the unit should be replaced. External condensation (on the outside face) is normal and actually proves the Low-E coating is working — it reflects heat so effectively that the external surface stays cold.