Fully Tempered Glass in Spandrel Applications

Assessing Residual Strength After Inner Light Has Shattered



Photo of Stéphane Hoffman, PE

Stéphane Hoffman, PE

Vice President Facade Engineering

Morrison Hershfield


Photo of Lawrence D. Carbary

Lawrence D. Carbary

Dow Corning Corporation




Recent years have seen an increase in the use of insulated glazing units (IGUs) in spandrel applications to visually blend the appearance between the vision and spandrel glass. There have been instances of glass breakage attributed to thermal stress for this type of design. A recent study indicates that IGUs in spandrel applications see higher thermal stresses than with traditional single glazed spandrels and that venting the spandrel cavity does little to minimize this increase in the thermal stress. Recent research supports the theory that the increased in thermal stress is leading to breakage of the inner light due to the lowered strength of heat strengthened ceramic opacified glass.

In response to this phenomenon considerations are being given to using fully tempered glass for the inner light when using a ceramic frit opacifier. This raises interesting questions regarding the performance of the glazing in the event of a failure of the inner light. While fully tempered lights have a long history of use in IGUs for safety reasons, it is not uncommon for these to have the occasional incidence of spontaneous breakage. However, in vision glazing units, these failures are readily apparent and promptly addressed. In spandrel applications, the failure of a fully tempered inner light may go unnoticed. This raises questions as to how much residual strength a unit with a shattered inner light would have to resist wind loads. The result of testing of structurally glazed IGUs with a fully tempered inner light that has been shattered demonstrated the residual strength was sufficient to resist an initial application design wind loads. The results provide guidance to designers considering the use of fully tempered glass in spandrel applications.


Recent years have seen an increase in the use of insulated glazing units (IGUs) in spandrel applications to visually blend the appearance between the vision and spandrel glass. As a

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There have been several recent instances of spontaneous glass breakage in insulated glazing units in spandrel applications with both sealed and vented spandrel cavities. The failure typically manifest itself in

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To test the performance of a spandrel IGU with a shattered fully tempered inner light, three identical insulated glazing units were subjected to a pressure test in accordance with ASTM

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The measurement for all three units were comparable both before and after the inner light was shattered (Table 1).

Sample #


Displacement in mm


1/2 span H



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Conclusion and Future Work

The testing demonstrated that the silicone structural insulating glass sealant was able to retain the outer light of glass in place despite the fact that the bond was now effected

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Rights and Permissions

ASTM (2016): “Standard practice for determining the load resistance of glass in buildings.” ASTM E 1300-16, West Conshohocken, PA.

EN 1863-2 (2004): “Glass in building – Heat strengthened soda lime silicate glass – Part 2: Evaluation of conformity/Product Standard” BSI, Brussels.

EN 12150-1 (2015): “Glass in building – Thermally toughened soda lime silicate safety glass” BSI, Brussels.

Krampe, P. (2014); The strength of enamelled glass. In Challenging Glass 4 & COST Action TU0905 Final Conference; Louter, C., Ed.; Taylor & Francis: London, p. 691.

Maniatis, I., and Elstner, M. (2016); Investigation on the mechanical strength of enamelled glass. In Glass Structures & Engineering; Springer: Switzerland, Vol. 1, Issue 1, p. 277.

Mognato, E., and Barbieri, A. (2013); The breakage of glass – Thermal shock and nickel sulfide inclusion. In COST Action TU0905, Mid-term Conference on Structural Glass; Mocibob, D. Louter, C., Ed.; CRC Press: Boca Raton, p. 155.

Natividad, K., Morse, S.M., and Norville, H.S. (In Press). “Tests of heat treated glass with full coverage ceramic frit.” J. of Architectural Engineering, ASCE.

Schwartz, J., Roppel, P., Norris, N. and Hoffman, S. (2017); Quantifying the Benefit of Venting Glazing Spandrels to Reduce Glass Breakage and Control Moisture, 15th Canadian Conference on Building Science and Technology.