BS EN 1279 (Parts 1–6)Approved Document L (Conservation of Fuel & Power)CIBSE Guide AReviewed Technical Specification
Insulating Glass Units (Double & Triple IGUs)
Hermetically sealed multi-pane glazing assemblies engineered for thermal transmittance control and condensation prevention.
Engineering Definition: An assembly consisting of at least two panes of glass separated by one or more hermetically sealed cavities containing argon or krypton gas and dehydrated with molecular sieve desiccant (BS EN 1279).
Material Construction Matrix
28mm High-Performance Insulating Glass Unit (IGU)
Thermal Transmittance:1.1 W/m²K
Acoustic Reduction:Rw 32 dB
Explode Layers
1
Outer Pane (Surface #1 & #2)(6mm Low-Iron Toughened)
6.0mm
2
Warm-Edge Spacer & Hermetic Seal(Composite Polymer & Butyl)
16.0mm
3
Argon Gas Cavity 90%(Noble Gas Fill)
16.0mm
4
Inner Pane (Surface #3 & #4)(6mm Toughened Low-E Soft Coat)
6.0mm
Physical & Mechanical Performance Characteristics
Safety Class:Determined by individual glass plies (inner/outer toughened or laminated)
Bending Strength:Shares wind load between plies via cavity pressure transfer; calculated per EN 16612
Thermal Shock Resistance:Low-E soft coats absorb solar energy; toughening required if thermal stress exceeds 40K
Fracture Behaviour:Depends on selected plies; safety glass required on inner or outer depending on impact zone
Typical U-Value (Ug):1.0 to 1.2 W/m²K (Double Glazed 28mm Argon + Soft Coat Low-E); 0.5 to 0.7 W/m²K (Triple Glazed 44mm Krypton)
Acoustic Reduction (Rw):Rw 31 dB (standard 4-16-4) up to Rw 46 dB (dissimilar thicknesses + acoustic laminated pane)
Max Sheet Dimension:Up to 3210mm × 6000mm (stepped or structural silicone glazed)
Density & Mass:2.50 kg/m² per total combined mm glass thickness (excluding spacer/gas weight)
Key Architectural Advantages
- •Regulatory compliance: meets and exceeds Approved Document L commercial non-domestic U-value targets
- •Substantial reduction in commercial HVAC heating and cooling operating expenditure
- •Elimination of internal cold downdraughts and perimeter surface condensation
Critical Engineering Constraints
- •Seals can fail prematurely if drainage paths in commercial window rebate are blocked (standing water degrades secondary seal)
- •Altitude barometric changes between factory and installation site can cause pillowing or dishing unless capillary breather tubes are fitted and sealed on site
- •Stepped units for structural silicone facades require UV-resistant secondary silicone seal (polyurethane cannot be exposed to direct sunlight)
Fabrication & Edge Processing Tolerances
Cut After Toughening:PROHIBITED (Catastrophic Fracture)
Heat Soak Testing (HST):Recommended to BS EN 14179
Units cannot be modified after perimeter sealant cure. Any breather tubes must be pinched and soldered at final elevation.
Architectural Specifier Checklist
Verify these technical criteria prior to contract documentation:
1Specify spacer type: warm-edge spacer bar (psi value ~0.035 W/mK) over standard aluminium spacer (psi ~0.075 W/mK).
2Identify coating surface location: Surface #2 (inner face of outer pane) for solar control; Surface #3 (outer face of inner pane) for passive heat retention.
3Check if structural glazing (SSG) is utilised: requires silicone secondary seal compliant with ETAG 002.
Frequent Commercial Applications
Network Procurement Routing
BuyGlass.co
Commercial cut-to-size glass manufacturing, direct supply, and transactional quoting platform.
Recommended Action: Calculate whole-window U-value and obtain commercial sealed unit supply quotations.
Proceed to BuyGlass.coReviewed by: Facade Thermal Specialist, BuyGlass Editorial Panel
Last Standard Verification: 2026-10-30