What Annex C Addresses
An insulating glass unit is not a collection of independent panes. Changes in external pressure, pane deformation and cavity conditions interact. Annex C provides the basis used by VitraLab to determine how the applied state is shared between the panes and sealed cavities of a rectangular DGU or TGU.
DGU and TGU System Definition
A DGU contains two panes and one cavity. A TGU contains three panes and two cavities. VitraLab defines every pane independently, including monolithic or laminated build-up, while retaining the complete pane-cavity sequence for the system calculation.
Mechanical Actions
Wind, barrier, maintenance and accidental actions can be applied through the EC10 workflow. The implemented connection evaluates the Annex C pressure interaction and passes the resulting pane-specific action to the reviewed structural-response route. ULS and SLS results are then assessed for each pane rather than assuming one pane always governs.
Cavity Reference Conditions
The sealing absolute pressure, sealing temperature and cavity width form part of the IGU reference state. These inputs remain editable because manufacturing, altitude and project conditions can differ. Both TGU cavities use the reported sealing reference while retaining their individual cavity widths.
Altitude and Barometric Pressure
An optional installation-altitude or pressure state represents a difference between sealing pressure and installation ambient pressure. VitraLab reports the resulting cavity and pane response as a standalone Annex C engineering-review state rather than mixing it silently into ordinary mechanical-action combinations.
Cavity Temperature States
Optional cavity-temperature input represents the difference between sealing and in-service cavity temperature. The resulting pressure change and pane response are reported separately. Project-specific temperatures must consider location, solar exposure, shading, ventilation and the specified IGU construction.
Laminated Panes Within an IGU
Any DGU or TGU pane can be monolithic or laminated. A laminated pane retains its action-specific equivalent thickness and shear-coupling basis when its structural response is evaluated. The IGU calculation does not replace the laminated-glass material and duration review.
Pane-Specific ULS and SLS Results
VitraLab reports the characteristic pane response, factored design actions, ULS stress utilization and SLS deflection ratio for the calculated combinations. The governing pane can differ between actions and limit states, so every pane result remains visible in the screen output and PDF report.
Current Rectangular-IGU Boundary
The current implementation covers the reviewed rectangular DGU and TGU Annex C calculation boundary through the validated scope recorded by VitraLab. Unsupported later provisions, other geometries and cases outside the implemented assumptions are not presented as calculated coverage.
Engineering Review and Draft Status
The 2024 prEN 19100-2 document is a draft submitted for enquiry and may change before publication. Engineers must verify cavity dimensions, sealing data, installation conditions, temperatures, loads, supports, glass build-ups, product information and every reported review note against the project requirements.
Frequently Asked Questions
What does Annex C calculate for an IGU?
Within the implemented rectangular-IGU scope, Annex C is used to evaluate the interaction between pane deformation, sealed cavity pressure and the applied pressure or environmental state.
Does VitraLab support both DGU and TGU?
Yes. The current EC10 workflow supports two-pane DGU and three-pane TGU systems with one or two sealed cavities respectively.
Are altitude and temperature effects combined with wind automatically?
No. The current public workflow reports optional altitude, pressure and cavity-temperature states separately as Annex C engineering-review states.
Can a laminated pane be used in a DGU or TGU?
Yes. Each pane can be defined independently as monolithic or laminated. Laminated panes retain the applicable action-specific equivalent-thickness and coupling basis.
Why are results reported for every pane?
Cavity interaction and pane stiffness affect load distribution. The governing pane can therefore change between actions, ULS resistance checks and SLS deflection checks.
Is the Annex C implementation based on a final standard?
No. It is based on the reviewed 2024 draft of prEN 19100-2 within VitraLab's validated implementation boundary. The output requires engineering review and does not establish compliance with a final adopted Eurocode.