Can you substitute spacers for insulating glass units (IGU)?

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The question of whether or not an installer can substitute the spacer that separates the outer from the inner glazing on an insulating glass unit is common in the industry and has far-reaching implications.  Our research (subject to independent verification is as follows):

  • ASTM E-1996-17 section A1.9.2 (referenced in the 7th Edition Florida Building Code (2020) and IBC-18) states:

“If the conditions in are met, a change in spacer type, shape, or dimension is allowed automatically”.

  • ASTM E-1996-17 A1.8.1.3 states

    “Substitutions for insulating glass shall only be made for systems with the impact resistant glazing structurally adhered to the frame or sash glazing leg or bed in the same manner and position as originally tested and approved”

  • In Florida (a reasonable level standard of care), 61G20-3.005(1)(d) allows for equivalency to be determined by a professional engineer
  • Also in Florida however, 61G20-3.005(1)(e) states that rational engineering cannot be used in lieu of a standard test.
  • ASTM E1996-14a requires one additional test whereas ASTM E1996-17 does not.

The question was proposed to the State of Florida via a declaratory statement by Al-Farooq Corporation (DS 2019-001).  It was concluded that the substitution is permitted as long as the standard is certified by an approved entity as meeting or exceeding the performance of the standard referenced by code.  Additionally when the question was proposed to TDI (December 2020 by this firm with client), this conclusion was also confirmed.

IGU Spacer Example
An example of a spacer in a structurally glazed impact insulating glass unit (IGU) – compliments Oldcastle Building Envelope Reliance StormMax Wet Glazed  Aluminum Curtainwall System (Large Missile Impact)

This leaves certain conclusions to be made for consideration by the evaluating design professional:

  1. This standard applies to impact units only where cyclical pressure is to be applied (non-impact would generally be approved with a comparable spacer approved by the evaluating design professional).  Wind Zone 4 of the code map would not be covered nor the High Velocity Zone section of Florida (Broward & Dade Counties and below).
  2. The system must be proven to be structurally glazed- That is the outer lite must be fully structurally adhered to a structural component of the frame
  3. In areas where ASTM E1996-14 applies, an additional test would be required unless the AJH permits the use of a more recent standard.


The evaluating / certifying design professional has final say in the approval of a spacer substitution. Documentation regarding both the certified and replaced spacers would be required to make the determination of substitution which should be based on the relative compressive nature of each material to permit/restrict the glazing lites to move & dislodge during cyclical events, especially after the glazing is hit & broken by a large missile.  Imagine a piece of laminated glass being broken and flexing in the thousands of cycles that is experienced during a category 5 event.  If the tested assembly had one spacer that held and it’s replaced with a weaker spacer and the system is not structurally glazed, movement and dislodgement could occur and lead to a breach in the building envelope & cascading damage to a partially enclosed building to ultimate catastrophic failure.  If the non-impact lite were to break and become dislodged and the spacer had more give, that would also contribute to excessive deformation during a cyclical event and failure.  The evaluating design professional is cautioned to carefully consider the worst-case scenario they are designing for with all required factors of safety.

Questions or comments with the above or the use of spacers in your product?  Contact Us do discuss. We’re experts in the field of commercial glazing.

Last Update: December 28, 2020  

December 28, 2020  Codes & Standards  
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