Eurocode 10: IGU Design, Stability, Detailing, and Worked Examples

Insulating Glass Unit Design

IGUs experience internal cavity pressure changes from three sources, treated as additional actions in EN 19100:

• Altitude difference (permanent action): Δp_H = 0.012 kPa/m · (H − H_production)
• Temperature difference (variable action): Δp_T = 0.034 kPa/K · (T − T_production)
• Meteorological pressure change (variable action): Δp_p = p_a − p_production

Combination factors for cavity pressure: ψ_cp,0 = 0.3, ψ_cp,1 = 0.3, ψ_cp,2 = 0.0.

BAM-Approach (new in EN 19100)

The BAM-Approach (Betti’s Analytical Method), developed by Galuppi et al. (2020), uses Green’s functions for accurate load sharing between IGU panes. It is introduced as Annex C of prEN 19100-2 and provides a more rigorous alternative to the traditional simplified method. The EN version extends the formulas from double to triple IGUs as well.

IGU load sharing: simplified method

For rectangular double IGUs under distributed loading, the load distribution between panes is governed by the insulating unit factor φ:

The stiffness partition for each pane is δ₁ = d₁³ / (d₁³ + d₂³) and δ₂ = d₂³ / (d₁³ + d₂³). The effective loading on each pane combines external loads, stiffness partition, and internal climatic pressure through the insulating unit factor. For IGUs with laminated glass panes, both “with composite effect” and “without composite effect” cases must be considered, because the stiffer the glass plate, the higher the internal pressure it attracts.

Recommended climatic values (NDPs)

Parameter	EN 19100 Recommended
Altitude change ΔH	+600 m
Meteorological pressure Δpmet	2 kPa
Temperature difference ΔT	+20 K

In-Plane Loading and Stability

Part 3 of EN 19100 covers glass elements loaded primarily in-plane: beams, fins, columns, and shear panels. These require stability analysis because glass elements are typically slender.

Imperfection values for stability design

Buckling Type	e0,length	e0,installation
Flexural + plate buckling	l0 / 333	hs / 2
Lateral torsional buckling	l0 / 450	hs / 2
Shear buckling	l0 / 1000	hs / 5

Second-order analysis is required when the elastic critical load ratio α_cr = M_cr / M_Ed < 10. Effective stiffness formulas (EI_z,eff and GI_T,eff) account for interlayer shear coupling in the stability analysis of laminated glass beams.

Deflection Limits

EN 19100 introduces three deformation classes, depending on what the deflection affects:

Class	Load Combination	Purpose	Example
1-SLS	Frequent	Aesthetical	Canopy drainage, IGU pillowing
2-SLS	Characteristic	Integrity / functionality	Ponding, airtightness, edge seal damage
3-ULS	Fundamental	Safety	Glass floor slipping from supports

Recommended deflection limits (Class 2-SLS)

Element	Support Condition	Limit
Glass component, all edges	Continuously supported	Centre: L/50
Glass component, 2–3 edges	Continuously supported	Free edge: L/100
Point-fixed glass	—	Centre: L/50, Free edge: L/100
Glass floor, all edges	Continuously supported	Centre: L/200
IGU, all edges	Continuously supported	Centre: L/50
IGU, point-fixed	—	Centre: L/150
Balustrade	Clamped at bottom	Gap max 50 mm between elements at 1 m height

Construction Rules and Detailing

The JRC guidance document and CEN/TS 19100 establish fundamental construction rules that apply to all glass structures, regardless of the design level:

• Glass-steel contact and glass-glass contact must be avoided. Hard contact creates stress concentrations that can initiate fracture. All contact surfaces must use intermediate layers (mortar, polymeric pads, neoprene).
• Glass panels must be fixed without excessive constraint. Over-constraining glass creates locked-in stresses that reduce the effective design resistance and can cause spontaneous breakage under thermal loads.
• Support materials must be durable for the expected service life. Degradation of gaskets, sealants, or setting blocks can lead to glass-to-metal contact over time.
• Humidity drying near laminated glass edges must be enabled. Trapped moisture at the interlayer edge accelerates delamination and reduces long-term bond strength.
• Thermal stresses must be considered where relevant heat absorption is present: partial shading, coatings, spandrel panels, proximity to heating devices. In some countries (France, Belgium) thermal stress is a formal load case; in Germany it is managed by specifying toughened glass where thermal risk exists.

Balustrades and Barrier Glazing

Barrier glazing is one of the most common applications where all four limit states (LSS-3) come into play. The revised DIN 18008-4 (2023) provides a useful reference for how barrier glazing is classified, and EN 19100 Part 2 formalises this through the FLS/PFLS framework.

Category classification (per DIN 18008-4)

Category A: The glass element solely carries the barrier loads.

• A1: Glass clamped at the bottom edge (cantilevering)
• A2: Glass fixed with point fixings or combinations of linear and point support (new in revision)
• A3: Glass spanning between supports (e.g., between posts)

Category B: Individual glass elements are connected by a continuous handrail. If one glass panel fails, the handrail redistributes the barrier load to adjacent panels. The revision removes the previous restriction to bottom-clamped cantilevering only; all combinations of linear and point support are now permitted.

Category C: Infill glazing only. The glass does not carry the barrier load; it merely fills the space between structural elements.

Breakage scenarios for barriers

The breakage scenario depends on edge protection:

• With sufficient edge protection: Only the inner glass ply (facing the traffic side) is assumed broken.
• Without edge protection: Both outer layers are assumed broken and are excluded from the calculation entirely.

Under EN 19100, these scenarios are formalised as FLS (impact during fracture) and PFLS (residual capacity after fracture) verifications, with reduced loading applied for the post-fracture check. The LSS assignment determines exactly which checks are required for each category and consequence class.

Worked Design Examples

The following examples are from the 2025 JRC Workshop presentation by Feldmann, Kasper, and Laurs:

Example 1: Insulating Glass Unit (CC1, LSS-0)

• Geometry: 1000 × 1250 mm, annealed float 8 | 16 | 8 mm
• Loading: Wind + climatic loads (BAM-Approach for cavity pressure)
• ULS check: σ_Ed = 11.24 MPa < f_g,d = 16.31 MPa → PASS
• SLS check: w = 3.14 mm < L/50 = 20 mm → PASS

Example 2: Glass Parapet (CC2, LSS-3)

• Geometry: 1500 × 1000 mm, TTG laminated 4 | 0.76 | 8 | 0.76 | 4 mm
• Loading: Barrier load h_k = 1.5 kN/m
• Three modelling levels compared:
  • Level 1 (no shear): σ = 112.5 MPa
  • Level 2 (EET): σ = 53.96 MPa
  • Level 3 (FEM): σ = 35.16 MPa
• ULS check: 80.94 < 103 MPa → PASS
• SLS check: 64 > 50 mm → FAILS (needs stiffer interlayer)
• PFLS check: With one pane fractured: 56.25 < 103 MPa → PASS

This example shows the dramatic difference between modelling levels: Level 1 predicts more than three times the stress of Level 3. It also demonstrates that SLS (deflection) can be the governing criterion even when ULS passes comfortably.

Example 3: Glass Fin (CC2, LSS-3)

• Geometry: 300 × 3000 mm, HSG 10 | 1.52 | 10 mm, fork bearings
• Loading: Wind w_k = 1.5 kN/m²
• Issue: Lateral torsional buckling is relevant (α_cr = 1.76 < 10)
• Method: FE analysis with imperfections (e₀ = 12.66 mm)
• Result: σ = 28.49 MPa < f_g,d = 40.83 MPa → PASS
• PFLS: Accounts for broken ply expansion affecting residual stiffness

References

1. Feldmann, M. et al. (2023). “The new CEN/TS 19100: Design of glass structures.” Glass Structures & Engineering, 8:317–337. doi:10.1007/s40940-023-00219-y (Open Access)
2. Feldmann, M., Kasper, R. & Laurs, M. (2025). “EN 19100 Design of Glass Structures: Key changes and benefits through design examples.” JRC Workshop “The Second Generation Eurocodes”, 5 June 2025.
3. Feldmann, M., Kasper, R. et al. (2014). “Guidance for European Structural Design of Glass Components.” JRC EUR 26439 EN. Free PDF from EU Publications Office
4. Kuntsche, J., Schuster, M. & Schneider, J. (2019). “Engineering design of laminated safety glass considering the shear coupling: a review.” Glass Structures & Engineering, 4:209–228. doi:10.1007/s40940-019-00097-3
5. Siebert, G. (2025). “Benefits of revised German code for glass design.” Glass Structures & Engineering, 10:5. doi:10.1007/s40940-024-00286-9 (Open Access)
6. Galuppi, L. & Royer-Carfagni, G. (2014). “Enhanced effective thickness of multi-layered laminated glass.” Composites Part B, 64:202–213. doi:10.1016/j.compositesb.2014.04.018
7. Galuppi, L. et al. (2020). “BAM approach for IGU cavity pressure calculation.” Based on Betti’s Analytical Method using Green’s functions.
8. CEN/TS 19100-1:2021 — Design of glass structures — Part 1: Basis of design and materials.
9. CEN/TS 19100-2:2021 — Design of glass structures — Part 2: Out-of-plane loaded glass components.
10. CEN/TS 19100-3:2021 — Design of glass structures — Part 3: In-plane loaded glass components.