Glazing Instructions

Glazing instructions are intended to assist the design professional in developing glass support systems that will minimize the possibility of glass breakage due to thermal and mechanical stresses, and to prevent premature failure of insulating and laminated glass products. Any violations, intentional or unintentional, of the Oldcastle Glass® glazing instructions will automatically void the warranty.

Cautions

1. The Oldcastle Glass® Insulating Glass (IG) warranty will be void under any of the following circumstances: if the unit is sitting in water or is installed in a glazing pocket that holds water; if the unit has not been stored and/or installed according to the Oldcastle Glass® glazing instructions; if the unit is installed in high-moisture environments (including, but not limited to, swimming pool enclosures and greenhouses); if solar-absorbing film, shades, blinds, or any foreign material are used on or near the surface of a unit, unless the product and the system details are reviewed by Oldcastle Glass® in writing; or if the unit is installed in high-vibration environments. Units installed in sloped glazing are not warranted unless glazing details are reviewed by Oldcastle Glass® in writing. Unit defectiveness caused by glass breakage or other damage is not warranted.
2. Oldcastle Glass® products cannot be used in any stopless glazing system (i.e., 2- or 4-sided structural silicone glazing) unless Oldcastle Glass® has given a prior written review of the glazing details. Failure to obtain a written review voids all Oldcastle Glass® warranties.
3. A determination of the compatibility between Oldcastle Glass® products and any other glazing system component (i.e., sealants, gaskets, tapes, setting blocks, metal finishes, etc.) is not the responsibility of Oldcastle Glass®. Failure of any Oldcastle Glass® product due to incompatibility with any other product voids all Oldcastle Glass® warranties. Acetoxy silicone used with neutralcure silicone IG units voids all Oldcastle Glass® warranties unless Oldcastle Glass® Technical Services preapproves the glazing details in writing. Incompatibility can occur between certain types of neoprene (including setting blocks and gaskets) and silicone sealed IG units under certain conditions. Setting blocks used in stopless glazing systems must be compatible with the Oldcastle Glass® insulating glass sealants. Sealant/gasket compatibility is not the responsibility of Oldcastle Glass®; seal failure due to any sealant/gasket incompatibility problems voids all Oldcastle Glass® warranties.
4. Installation of units without all sides being structurally supported (i.e., butt-glazed without interior mullion support) voids all warranties unless Oldcastle Glass® has given a prior written review of the glazing details.
5. Do NOT use razor blades or broad knife blades of any kind to clean glass. Oldcastle Glass® is not responsible for scratches or damage caused by glass cleaners and other construction tradesmen. The following glazing instructions are intended to assist the design professional and installer. Additional glazing recommendations and guidelines, provided by GANA, AAMA and IGMA, must also be followed.

Glass Handling

Care must be exercised in the handling and the glazing of glass to prevent damage to the glass edge. The glass must not contact the framing members during glazing. A rolling block should always be used when rotating glass to avoid corner damage. Glass must be protected from weld splatter, and blasting and other impact damage. Alkali or fluorinated materials released from concrete or masonry during rainstorms can stain or etch glass. Weathering steel releases oxides while aging, which can result in stained glass if proper periodic cleaning is not done. Solutions used to restore or neutralize masonry surfaces can attack first-surface pyrolytic, reflective coated glass.

Glass Storage

Glass should be kept on a lean of 5-7° from vertical using broad, sturdy uprights. Never store glass in sunlight without using an opaque cover to protect it. Glass should be stored in a dry, clean and cool location where the temperature is above the dew point. Circulation of dry, cool air is required especially after periods of high humidity and cyclic temperatures. If glass must be stored outdoors, use tarps or plastic coverings to protect it from getting wet, and vent periodically to prevent moisture accumulation. Repeated wetting and drying of glass surfaces can result in staining or etching of the glass.

Glazing Frames

Frames must be square, in plane, free of any internal obstructions and structurally adequate.

• Diagonal differences–1/8" maximum
• Plumbness deviation–1/16" per 6' maximum
• Corner joint misalignment–1/32" maximum
• Sill deflection–1/8" maximum (when a unit is on setting blocks at quarter points).
• Maximum allowable wind load deflection = unit's long dimension in inches divided by 175 or 3/4", whichever is less.
• Expansion joints must be located between glazed openings.
• Two-span vertical mullions should have the dead load (fixed) anchor located at their midpoint. Three-span vertical mullions should never be used.
• Horizontal expansion joints should not be further apart than 20 feet or every 4 lites of glass, whichever is less. Expansion should be from the center toward both ends, to minimize joint movements and thereby reduce stresses on sealants and connectors.

Edge and Face Clearance, and Bite

The glazing system must have adequate edge and face clearance to cushion the glass, thermally isolate the glass and framing members and prevent glass-to-metal contact. Adequate bite is required to provide a proper seal against air and water infiltration; however, excessive bite will increase thermal breakage. Refer to the chart for proper clearance and bite values.

Setting Blocks

Glass should be set on 2 identical setting blocks with a Shore A Durometer hardness of 85 ± 5. They should be an equal distance from the centerline of the glass at the sill quarter points, but not less than 6" from the corner edge. Each block should be sized to provide 0.1" of length per square foot of glass area, but not less than 4" of length. The setting block should be 1/16" less than full-channel width. The height should provide the recommended nominal bite and minimum edge clearance for the glass. When a lock-strip gasket glazing system is used, each setting block should be sized to provide 0.4" of length per square foot of glass area, but not less than 6" of length. The lock-strip gasket manufacturer should recommend the height of the blocks.

Weep Systems

The glazing system must be designed to prevent the accumulation of moisture in the glazing channels for prolonged periods. This applies to dry, wet and lock-strip glazing. Oldcastle Glass® recommends 3 weep holes, 3/8" in diameter or equivalent, per sill–one at the center point of the span and one each, 4" inboard of the unit corners. For a door and window wraparound gasket, provide sufficient weep holes to prevent retention of water at the unit edges.

Antiwalk Blocks

These blocks of 30 to 40 Durometer neoprene or silicone must be used in dry gasket glazing, one per jamb. Blocks are to be 4" high, 1" wide and of a thickness to allow a 1/8" clearance between the block and unit edge. Glazing sealants must not fill the edge clearance voids.

Structural Gasket Glazing (Lock-Strip Glazing)

This system must have a continuous wet sealant applied as a cap bead to the exterior glazing leg.

Wedge Gasket Glazing

The wedge must be inserted starting at the midpoint of the unit's width and height. Wedging should never be started at a unit's corners.

Pressure Wall Gaskets

These gaskets must apply their sealing pressure onto the glass uniformly, 1/8" to 9/16" from the unit's edge of not more than 10 pounds per linear inch and not less than 4 pounds per linear inch. Torque-controlled wrenches are required to achieve uniform bolt tightening. Tighten bolts at the quarter points of the sill, then the quarter points of the head, then quarter points of jambs, and then the remaining bolts.

Typical Face and Edge Clearance and Bite

Capillary Breather Tubes

These are recommended for use with IG units that experience an elevation difference of 2,500 ft. or more in transportation or installation. Tubes must be sealed immediately upon arrival at the destination by crimping them tightly in two places. The capillary tube should be installed at the vertical dimension of the unit, with the crimped end pointed downward along the vertical edge.

Glazing and Caulking

Compounds containing plasticizing oils or solvents may not be compatible with a unit's edge seal. (Compatibility must be verified.)

Glazing Sealants

Structural gaskets and pressure gaskets must remain resilient for the unit's warranty period.

High-Risk Installations

Thermal Stresses

Thermally induced edge stresses are usually the result of the warmer center portion of a glass lite being exposed to solar energy wanting to expand more than the cooler edges. The rate at which the glass absorbs energy is dependent on its type, size, thickness and shape and how it is isolated from the framing system. Other factors are building orientation, interior shading devices, exterior shading patterns, heating register location, etc. Tempering or heat-strengthening increases glass edge strength and decreases the chances for thermal breakage. The following conditions must be taken into account when considering the effects of thermal stresses:

1. Interior Heat Traps These situations occur when there is inadequate air circulation to properly remove heat from behind the glass. Spandrel areas are a good example of glass that must be tempered or heat-strengthened to offset the rise in temperature. In vision areas, air movement must not be restricted. Suspended ceilings must be well to the room side to allow natural convection. Or the head area should include vents that provide a minimum of one square inch of ventilation for each inch of glass width. Or the glass should be heat-strengthened or tempered.
2. Interior Shading Draperies, venetian blinds or other interior shading devices must be hung with space to permit natural air movement over the room side of the glass. The following criteria must be met to avoid formation of a heat trap:
   • Minimum of 1-1/2" of clearance required, top and bottom, or one side and bottom, between the shading device and surrounding construction.
   • Minimum of 2" clearance between the glass and the shading device.
   • Heat/cooling outlets must be to the room side of the shading device, with airflow directed away from the glass.
   • Use mechanical stops to prevent complete closure of blinds to 60% of closed position. Heat-strengthening or tempering of the glass may be necessary to offset the effects of a lack of adequate ventilation.
3. Exterior Shading Shadows cast by overhangs, surrounding structures, trees and shrubbery can create shading patterns on the glass, creating thermal edge stress. Maximum stress occurs when 25% or less of the area of a lite is shaded and the shade includes more than 25% of the perimeter. Generally, horizontal, vertical and diagonal shading patterns are not as critical as shading that combines several patterns. Double diagonal shading is generally the most critical pattern. See the sketches (below) of typical shading patterns that are labeled "Acceptable Shading", "Marginal Shading" and "Harmful Shading". It is recommended that Oldcastle Glass® Technical Services review designs to determine whether heat-treating is required. (See the following page for information.)

Exterior Shading Patterns

Acceptable Shading: More than 50% of the glass area is in shade.

Marginal Shading: More than 25% of the glass area is in shade.

Harmful Shading: Less than 25% of the glass area is in shade and more than 25% of the perimeter glass is in shade.

Technical Services

Oldcastle Glass® offers a wide variety of technical services, including a review of glazing details, glass thickness versus wind load recommendations, glass deflection analysis, thermal stress analysis, glass performance information and glass breakage analysis.

Thermal Stress Breakage

Thermal stress in glass is usually caused by the temperature differences between the covered edges and the center portion of the glass. Thermal stress in the glass increases as the center-of-glass and edge temperature differences increase. The probability for glass breakage increases as the thermal stress increases.

It is advisable to perform a project-specific thermal stress analysis for each project where thermal stress breakage is a concern. Many factors, besides the glass type, must be considered in a thermal stress analysis. These include, but are not limited to, the window frame material and color; glass shading from overhangs and balconies that create unusual shading patterns across the glass surfaces; blinds and window treatments; air and heating vents; blowing on the glass; glass size; as well as the direction and elevation of the sun.

Thermal stress breakage of annealed glass will occur when the thermal stress exceeds the glass edge strength. Tempering or heat-strengthening will normally prevent glass breakage due to thermal stress.

The more heat-absorbing the glass is, the higher the thermal stress will be. Tints and reflective glasses have higher solar absorption and are therefore more susceptible to thermal stress breakage.