EN 16612 Annex D Stiffness Families & EN 16613:2025 — Explained
Two Standards, Different Jobs
Designing laminated glass in Europe involves two related but distinct standards. They are routinely conflated; getting them straight matters because they are now updated on different schedules and increasingly cite each other rather than duplicating content.
| Standard | What it does | Where the 12 load cases / stiffness families live |
|---|---|---|
| EN 16612:2019 — Glass in building — Determination of the lateral load resistance of glass panes by calculation | Calculation method (effective-thickness, ω shear-coupling) | Annex D — 12 standard load cases, families 0/1/2, ω tables |
| EN 16613:2025 — Glass in building — Laminated glass and laminated safety glass — Determination of interlayer viscoelastic properties | Test method for measuring G(t, T) | Not here. EN 16613 produces the property data that feeds the EN 16612 Annex D classification. |
What changed in EN 16613:2025: The 2025 revision is scoped strictly to property determination. The load scenarios and stiffness families that some readers remember from earlier drafts of EN 16613 are not in the 2025 standard — they belong to EN 16612:2019, Annex D. The preferred test geometry has also moved from ISO 6721-4 (tensile vibration) to ISO 6721-10 (parallel-plate oscillatory rheometer).
The 12 Standard Loading Conditions (EN 16612:2019 Annex D)
Annex D of EN 16612:2019 defines the following load cases. Each pairs a representative duration with a representative temperature for one design scenario. Engineers check the interlayer's shear modulus at every relevant case before choosing a stiffness family.
| # | Condition | Duration | Temperature | Category |
|---|---|---|---|---|
| 1 | Wind gust | 3 s | 35°C | Wind |
| 2 | Wind gust (cold) | 3 s | -20°C | Wind |
| 3 | Wind storm | 10 min | 35°C | Wind |
| 4 | Wind storm (cold) | 10 min | -20°C | Wind |
| 5 | Balustrade (no crowds) | 30 s | 30°C | Balustrade |
| 6 | Balustrade (crowds) | 5 min | 30°C | Balustrade |
| 7 | Maintenance load | 30 min | 40°C | Imposed |
| 8 | Snow (3 weeks) | 3 w | 0°C | Snow |
| 9 | Snow (5 days) | 5 d | 20°C | Snow |
| 10 | Climatic (6 hours) | 6 h | 40°C | Climatic |
| 11 | Climatic (12 hours) | 12 h | 60°C | Climatic |
| 12 | Permanent load | 50 yr | 60°C | Permanent |
Why these specific conditions?
Each case is a worst-case combination of duration and temperature for its loading category. Wind gusts are checked at 35°C (summer, when interlayers are softest under short loads) and at −20°C (winter, when glass is more brittle). Permanent loads are checked at 60°C because roof-mounted or sun-exposed glass can reach high temperatures over decades of service. The two balustrade cases distinguish handrail loading without crowds (30 s) from sustained crowd loading (5 min).
Stiffness Family Classification
Annex D groups interlayer materials into stiffness families based on their shear modulus at the 12 standard conditions. A material belongs to a given family if its stiffness meets or exceeds the family threshold at every relevant condition. The family then maps to a tabulated shear-coupling coefficient ω (between 0 = layered limit and 1 = monolithic limit) used in the effective-thickness calculation.
Family 0 vs. Family 1 vs. Family 2
- Family 0: No shear transfer assumed. The interlayer is treated as having negligible stiffness (ω = 0, layered limit). Conservative fallback when no characterisation data are available.
- Family 1: Partial shear transfer under short-term and medium-term loading (wind, balustrade, snow). Meaningful structural contribution for these scenarios.
- Family 2: Significant shear transfer across all loading conditions including long-term (climatic, permanent). Only the stiffest interlayers (typically ionomer products such as SentryGlas / SentryGlas Xtra) qualify.
Design Implications
The stiffness family determines how the laminated glass element is modelled in structural calculations per EN 16612:
- Family 0 interlayers require designing the glass as a layered system (no coupling between plies). This results in thicker glass and higher cost.
- Family 1 interlayers allow the engineer to account for partial composite action under wind and imposed loads, reducing glass thickness requirements for these load cases. However, permanent and climatic loads must still be checked without interlayer contribution.
- Family 2 interlayers provide composite action even under long-term loading. This enables the thinnest glass solutions and is essential for applications like structural glass beams, fins, and heavily loaded facades.
Cost impact: Moving from Family 0 to Family 1 can reduce glass thickness by 20–30% for wind-governed designs. Moving to Family 2 enables applications that are structurally impossible with lower-family interlayers.
Common Interlayer Performance
Indicative shear modulus values for common interlayers at three representative Annex D conditions. They illustrate the range of stiffness behaviour; verify against the relevant manufacturer datasheet for design use.
| Material | Wind gust (3 s, 35°C) | Maintenance (30 min, 40°C) | Permanent (50 yr, 60°C) | Typical Family |
|---|---|---|---|---|
| Trosifol Clear | 0.5 MPa | 0.2 MPa | 0.06 MPa | 0 |
| Trosifol Extra Stiff | 5.8 MPa | 0.6 MPa | 0.16 MPa | 0–1 |
| Saflex Structural | ~5 MPa | ~0.5 MPa | ~0.2 MPa | 0–1 |
| SentryGlas | 102 MPa | 11.4 MPa | 0.74 MPa | 2 |
| EVA | 4.2 MPa | 2.4 MPa | 0.88 MPa | 0–1 |
The difference between Trosifol Clear (~0.5 MPa) and SentryGlas (~102 MPa) under a wind gust represents a factor of 200 in interlayer stiffness. This difference translates directly into dramatically different structural behaviour of the laminated glass.
Practical Workflow
For a practising engineer, the typical workflow is:
- Identify the governing loading conditions for your application (e.g., a facade in Northern Europe: conditions 1–4, 8–9, 10–12).
- Obtain the interlayer shear modulus at each relevant condition. Use manufacturer datasheets, the declared stiffness-family classification, or characterisation data measured per EN 16613:2025 (ISO 6721-10).
- Calculate the effective thickness of the laminated glass per EN 16612, using the shear modulus (or the ω from the declared family) to determine coupling between glass plies.
- Verify that stresses and deflections meet the requirements of EN 16612 for each loading condition.
Instant EN 16612 Annex D Lookup
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