WHAT GLAZING CONTRACTORS NEED TO KNOW ABOUT ARCHITECTURAL GLASS AESTHETICS AND THERMAL PERFORMANCE

Read Glass Magazine’s Glazier Bulletin “Architectural Glass Design Assist” What glazing contractors need to know about architectural glass aesthetics and thermal performance, written by Gary McQueen, Architectural Design Manager for J.E. Berkowitz.

Architectural Glass Design Assist

What glazing contractors need to know about architectural glass aesthetics and thermal performance

By Gary McQueen

McQueen is architectural design manager for JE Berkowitz LP, jeberkowitz.com. He can be reached at 800/257-7827 or gmcqueen@jeberkowitz.com.

JEB 3Seal warm-edge structural silicone spacer introduces a unique t-shaped design and acrylic adhesive (a third seal) that mitigates PIB migration. Additionally, 3Seal is robotically applied with hot-injected PIB primary seal, delivering a straight sightline, suited for two-side structurally glazed, four-side structurally glazed and cold-form bent insulating glass unit installations. 3Seal warm-edge silicone spacer increases sightline temperatures, which directly impacts total system U-value.

As design-assist agreements become more prevalent, glazing contractors must recommend architectural glass products that meet stringent aesthetic and thermal performance requirements early in a project’s design phase. As part of this process, educated owners and architects expect the glazing contractor to deliver high-quality finished products that not only look great, but also meet evolving energy codes.

In order to do so, glazing contractors should be well-versed in the aesthetic and thermal concerns of specific architectural glass products, and know when to consult a quality architectural glass fabricator for assistance. Below are several aspects of architectural glass specification that are of great importance to today’s glazing contractor.

Aesthetics

IG sightline

The insulating glass unit sightline, the imaginary line separating the IGU edge from the vision area, running along the top/interior surface of the spacer, is a major aesthetic concern for many architects and façade consultants. Over time, design and wind loads may force the polyisobutylene primary seal, which never cures, into the insulating unit’s vision area, an occurrence known as PIB migration. There is no ASTM standard for PIB migration, but rather a Glass Association of North America bulletin highlighting general sightline tolerances. Glazing contractors should be aware of advancements in spacer and edge seal technology that answer the common sightline concerns of architects and consultants.

Quality controls

Two commonly specified quality controls for heat-treated architectural glass are bow & warp and roller wave distortion.

• Bow & warp is any curve, bend or other deviation from the flatness of glass. High-quality architectural glass fabricators have state-of-the-art tempering ovens, machinery, digital photography technology, and ISO-9001 quality control procedures in place to meet much tighter tolerances than what is currently considered industry standard. As a result, glazing contractors should recommend the architect specify bow & warp at a maximum of half of the ASTM C 1048 Standard for ¼-inch thick monolithic float glass.
• Roller wave distortion is a repetitive wave-like departure from flat glass. Glazing contractors should insist the architect specify roller wave distortion targets not exceed .003 inch as measured peak to valley at the center of glass, and .008 inch at the leading and trailing edge of the lite of glass. There is no ASTM standard for roller wave distortion, but rather an industry recommendation.

There are a number of other aesthetic requirements and quality control procedures that should be specified to ensure high-quality architectural glass for the project, and glazing contractors should consult with a high-quality architectural glass fabricator to determine the best products and procedures.

Thermal performance

From a thermal performance standpoint, project teams must identify high-performing products that help meet tighter energy codes targeting lower total U-values and solar heat gain coefficients.  For example, next generation triple-silver low-emissivity coatings, both neutral and reflective, drive lower solar heat gain, and can help a project meet SHGC requirements for specific elevations or total wall performance.

Glazing contractors should also be aware of the products that reduce center of glass U-value as well as total U-value (framing system + insulating spacer + glass makeup).  As an example, room-side or pyrolytic low-E coatings are typically fabricated on surface No. 4 of a double-glazed insulating unit, and can reduce center of glass U-values by as much as .04 or .05.

Understanding evolving architectural glass aesthetic and thermal requirements can help glazing contractors make valuable recommendations during the design-assist process.  It is important glazing contractors consult with an architectural glass fabricator to address potential aesthetic and performance concerns as early as possible.