Staying Within the Lines: Updated Guidelines Ensure IGUs Give Their Best Performance
By Amy Becker
Not unlike a homeowner investing in the long term, fabrication of insulating glass units (IGUs) within acceptable dimensional tolerances is an investment in long-term performance and their associated benefits. Supporting fabricators’ abilities to dial this in, the Fenestration and Glazing Industry Alliance’s (FGIA’s) Dimensional Tolerances Task Group is hard at work updating IGMA TB-1200, Guidelines for IG Dimensional Tolerances.
Because a perfectly fabricated IGU is difficult to achieve, certain levels of slight shifting can be tolerated with no compromise in performance. However, it is essential that these expertly determined dimensions are honored during fabrication. In the event that tolerances stray too far, the IGU runs the risk of possible problems, such as water infiltration and absorbing excess glazing stress.
The consequences of exceeding these tolerances can be serious. A “little off” can mean that, instead of a product performing as designed, it doesn’t have the necessary space to move in relation to the frame and other components, and there can be glass contact, incorrect pressure, and other issues. Many of these things could mean the integrity of the glass is now compromised and spell trouble down the road.
IGMA TB-1200 Updates
Originally released in 2016, this document has been updated to read more like a set of guidance and guidelines as opposed to mandatory requirements. Small changes include a streamlined introduction, a succinct scope, and updated language in the tables. Generally speaking, the document addresses the installation of insulating glass as double and triple IGUs, taking into account the glass thickness, spacer thickness, and sealant application. It also recommends focusing on glazing cavity size, allowable edge seal pressure, setting block type, allowable minimum edge seal system, and sightline design requirements as the IGU glazing system is being designed.
In the section on Measurement Technique, a recommendation has been added that all measurements be taken with the same device. In addition, that device should offer adequate precision, resolution, and repeatability for a given tolerance to ensure the most accuracy. For example, the document recommends a ruler or tape measure to determine an IGU’s height, width, and diagonal value. For the unit’s thickness and edge alignment, a caliper or micrometer is recommended.
As noted, the new document updates tables of tolerance values for annealed lites, heat-treated lites, and laminate/glass lites. The guideline also includes tables for thickness and size tolerances for nominal monolithic glass, pattern glass lites, and wire glass lites. Another table covers laminate thickness designations for monolithic, patterned and wired, and heat-treated glass tolerances. For IGUs with one or more lites of laminated glass, a table is provided for the longest individual lite width and height and the maximum IGU squareness tolerance.
As with all FGIA guidelines, this document taps the collective expertise of IGU fabricators, material suppliers, designers, and consultants. Informed by their experiences with IGUs, these tolerance values have been established. Fabricators and specifiers can also reference IGU manufacturer dimensional tolerance guidelines for individual products to supplement this guidance.
Amy Becker is a glass products specialist for the Fenestration and Glazing Industry Alliance (FGIA).
abecker@fgiaonline.org
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