General guidelines for handling and storage glass

The document include in this section are designed to help avoid problems in order to storage and handling on site, in factory and customers premises. They can be included with every project to avoid serious damage to glass that may result from improper handling or storage procedures.

Contact to Millet’s technical service customer & Sales representative for additional recommendations and cautions.

According to GANA, Glazing Manual, IGMA, Insulating Glass Manufacturing Quality Procedure (TM-4000-02) proper suggestion procedures for general guidelines for handling and storage glass.


MILLET Glass Industry offers these recommendations for handling and storage as a General Guide only. It is the responsibility of the user of this Guidelines to ensure that glass is selected and installed by competent professionals in compliance with all relevant laws, rules, regulations, standards and other requirements.

MILLET makes no warranty or representation and assumes no liability or responsibility in connection with any information contained in this Guidelines. MILLET assumes no liability or responsibility in connection with any modifications to or adaptations of this Guidelines by any user, purchaser or other party, or in connection with the use or misuse of any information contained in this Guideline, this General Guidelines is intended to be voluntary and not binding. MILLET does not “approve” or “endorse” any products, services or methods mentioned herein. This General Guidelines should not be referenced in any way which would imply such approval or endorsement.

Drawings contained herein are not to scale.

Handling and storage

Storage of glass in factory and customers premises

Types of storage

There are a number of different types of storage racking available, each type designed for either the size of glass, the type of warehouse, the method of handling available or the volume of glass needing to be stored or handled. Whether the method of storage used are wall racks, end caps, toast racks, glass supporting frames, A frames or pallets, there are specific guidelines for each type to ensure safe and appropriate storage which should be discussed with the manufacturer or distributor of the storage racks prior to installation. Please contact our sales office should you require more information.

Storage of glass on site

Whilst each site will be different and the areas to focus on possibly unique, there are a number of potentially hazardous areas which need to be considered. These include, but are not limited to:

• The suitability of the ground to safely store and protect the glass with suitable racking.

• Sufficient access and space to safely unload maneuver and store the glass.

• The ability to provide dry storage conditions out of direct sunlight; this is applicable to all types of glass but especially tinted or toned glass which absorbs a high % of the heat.

• The need to protect the glass from accidental damage or site contamination caused by other materials and building practices which may induce breakage or damage to the glass such as welding, sandblasting, floor sanding etc.

• Protection from freak weather conditions, such as high winds.


Handling of glass

Glass is a potentially dangerous material, particularly if handled incorrectly. It is imperative that suitable training must be given to all employees who handle glass either in the warehouse or on site to ensure that they can best protect themselves and those around them. This applies to all types of glass, of any size.

Whilst mechanical means of moving the glass should be initially investigated and adopted, it is recognized that this is not always possible. If the glass has to be moved manually, the load associated with the glass must be able to be suitably managed by the number of people moving the glass, with any physical restrictions relating to the people involved being noted and managed accordingly. This may be achieved through the use of straps or slings, webbing lifts, suction pads or glass carriers.

Whilst the size and the thickness of a particular piece of glass will determine the number of people required to lift the glass, a number of key factors apply regardless:

• Correct PPE is being used at all times.

• The condition of the glass must be checked, in particular checking for any venting or glass runs present.

• Ensure that there is plenty of space available to maneuver, that any potential obstacles have either been noted and/or moved and that the pathway is dry.

• The destination of the glass has been prepared with appropriately prepared racking or storage in place.

• A safe lifting posture should always be adopted.


When lifting the glass, ensure that it is kept as upright as possible without any flexing of the glass taking place.  Upon the delivery of the glass check marks and labels on the crate, pack or glass to ensure compliance with the specification.

The edges and corners of glass and double-glazed units are especially vulnerable during handling, storage and installation. Inspect the cut edges of the glass for excessive flaws such as shells or feathers that can compromise the strength and mechanical performance of the glass.

Check all surfaces for any signs of mechanical damage or etching. Particular care is necessary as edge or surface damage may cause subsequent unexpected failure.

Glass that is not stored safely can present considerable risk of injury.



Store panels on edge at an angle of 5° to 7° from the vertical, with sufficient lateral support to prevent bowing, in a clean dry, ventilated place, avoiding direct sunshine and other sources of heat. Set the glass panes on strips of wood or other soft material, to avoid contact with hard materials such as metal, stone or concrete. Avoid contact with alkaline materials such as lime and cement.
Delivery, handling and site storage methods must be agreed for each site. Any form of factory applied protection, such as cork pads or shrink-wrapping, must not be removed until the glass is ready for installation.

When the packaging has been removed, the glass must be covered to prevent the ingress of dust and grit that may cause subsequent scratching.

Glass is not normally considered corrodible by contact with water providing it is allowed to dry properly.

However, if water is allowed to remain in contact with the glass for extended periods it can become alkaline and will attack the glass surface. If not stored properly water can penetrate between panes of stacked glass by capillary action; this moisture is then trapped between the panes and will tend not to dry naturally, eventually “welding” the glass sheets together.

If any moisture or condensation is apparent between the panes of stacked glass, separate immediately and dry thoroughly, otherwise permanent staining may result. Re-stack in a more suitable location in accordance with the advice provided above and the recommendations of GANA


The insulating and energy saving characteristics of Insulating Glass Units (IGU’s) are well documented, however their handling and installation require careful consideration, over and above those glazing methods often used for single glazed products.

IGU’s can be manufactured in varying forms with a variety of seals and spacer materials. It is vital that these materials are compatible with glazing sealants and setting blocks used, and are glazed in such a manner to ensure they deliver the performance benefits over the life of the windows in which they feature.

The airspace within an IGU is a hermetically sealed cavity (i.e. it is sealed away from outside atmosphere and environment). The perimeter seal of an IGU is the only protection the air space has against outside environmental factors. Framing systems which cater to single glazed window construction may need some modification to ensure that IGU’s are glazed in a way to allow maximum protection of these seals.

Moisture exposure is recognized as a major risk as well as non-compatible sealants and setting blocks.

Glazing systems for IGU’s can be defined into two types, drained and non drained. Glazing recommendations for both will differ.

Please read carefully and follow these basic steps before installation to ensure the IGU’s that you install are both covered by our lengthy warranty (10 years), and given the best environment to survive the life of the window itself.

 A vital reference for all installers of IGU’s should also be made to the current standard for Insulated Glass Units (ASTM E 2190), IGMA Recommended Practices for Vertical Field Glazing of Organically Sealed Insulating Glass Units Manual, Flat Glass Marketing Association Manual, GANA’s instructions regarding installation and/or maintenance of the unit, including written proof of routine maintenance (consult Glass Association of North America Glazing Manual);


In summary the essence of recommendations revolves around the following 3 principles:
1. Keep the edge seal away from water and water vapor
2. Ensure the compatibility of glazing materials (Silicones/rubbers/setting blocks)
3. Protect the edge seal from Sunlight

“The life span of IGU’s may be significantly reduced if they are installed incorrectly. In addition, manufacturer’s warranties against seal failure may be invalidated if the insulating glass unit is installed incorrectly. Therefore, it is important to ensure the glazing system is suitable.”


1. Stack on edge in a vertical position at 90° to its base support, which is inclined at 5 to 7 degrees, with cushioning between floor and edges.
2. Do not stack more than six (6) deep without intermediate support for each stack.
3. Store in a dry environment away from direct sunlight. Prolonged exposure to dampness may affect IGU seals and lead to product breakdown.
4. Do not cover with plastic, as condensation may damage edge seals.
5. Never store or transport horizontally.
6. Carefully remove all labels after glazing. Large dark colored labels can be a source of heat absorption and give cause for thermal risk when used in conjunction with annealed components.
7. Do not damage edges in any way before or during installation. Even minor local shelling may increase risk of glass breakage.
8. Never attempt to nip or grind edges, as this can damage the seals and lead to glass breakage.
9. Damaged IGU’s must not be glazed.
10. Protect IGU’s during building works. Guard against contact with wet cement or other alkaline materials released during rain from concrete or masonry, as this can cause staining.
11. If glazing in high altitude locations, units may require pressure equalization tubes (also known as capillary tubes). This must be noted on the purchase order. Please contact our sales office should you require more information.




1. Frames, beads and fixings must be adequate to support and restrain IGU’s, withstand wind loadings, IGU weight and building movements: • Ensure all glass framing members are plumb and square.

• Width of the frame rebate must be sufficient to accommodate the thickness of the IGU, plus face clearance plus bead.

• Never force units into the frame.

• Ensure glazing rebates and drainage weep holes are free from debris and obstructions.

• Glazing surfaces must be free of moisture, oil, dirt, grease and other contaminant material o Screws, bolts or other obstructions must not protrude into the glazing channel.



1. IGU’s must have adequate edge clearance for the full thickness of the unit:

• Setting blocks must allow drainage to pass to weep holes.

• Any point loading must be prevented.

• Edge cover should be a minimum of 12mm.


Sealing and Drainage

1. In the case of un-drained systems, all external junctions of glass and frame must be effectively sealed against penetration of weather: • Glazing materials must achieve watertight glazing seals over the life of the warranty period.

• Water / moisture cannot be allowed to enter inside the glazing, as it will enter into the seal construction as water vapor and reduce the life-time of the sealed airspace.

2. In the case of drained systems: • Install IGU’s so that lodgment of water in the frame is prevented in the proximity of the edge, as prolonged contact with moisture may lead to seal failure.

• Ensure rebates are well drained with a minimum of 2 weep holes per sill, each 7mm x 3mm at maximum 500mm centers and can operate over the life of the warranty period.

• Ensure there are no nails or similar material within the rebate.

• Timber or concrete frames, where in contact with glazing compounds, must be completely sealed with an appropriate sealer.

3. A list of compatible glazing sealants for both polysulfide and structural silicone sealants are separately available and should be checked for compatibility



1. Protect polysulphide IGU edge seals from UV rays (commonly found in natural sunlight), which may break down the compounds contained within the seals. Where edge seals are exposed, it is crucial to specify structural silicone seals which are designed to withstand this UV exposure in external conditions.

2. Do not expose IGUs to chemical fumes or gases other than those present in normal clean atmospheric air, or to radiation of any type other than normal sunlight.



Important summary note:

All units are covered by our warranty against manufacturing defects (listed separately).

Should any IGU panels exhibit traces of internal moisture or break-down, an investigation must be made as to the cause. In the case of drained systems, any traces of moisture need a clear path to drain away and will need to be demonstrated.

In the case of un-drained systems (more common with timber windows) upon removal of glazing beads and seals, internal glazing pockets and materials need to be free of any moisture or traces of moisture. In respect to glazing recommendations for non-drained systems we confirm and re-enforce the need for systems to prevent any chance of moisture from entering inside the glazing system for the term of the warranty.

Any IGU installed outside the above guidelines, allowing secondary seals to have prolonged exposure directly to moisture or moisture vapor, will not be covered by the product warranty.


Design Review

The design professional(s) (architect, engineer, specifier) is responsible for selecting glass suitable for its intended application. Among other design criteria, the following items should be considered during the design review:

• Loading requirements, glass strength and thickness, and thermal stresses.

• Thermal performance requirements for glass and framing (U-factor, condensation resistant factor (CRF), etc.).

• Design of edge seal for structurally glazed IG units.

• Material compatibility.

• Acoustical considerations.

• Daylighting, glare and occupant-comfort considerations.

• Temperature extremes to which the wall will be exposed.

• Location and type of exterior shading and its effect on the glass.

• Location of interior shading devices, heating and cooling outlets, blind or drapery pockets, and ventilation grilles that will affect thermal stress of the glass..




 Proposed location and type of fire safing between stories.


 Location, type and thickness of spandrel glass insulation and vapor barriers.

Drip ledge at head of all glass to minimize glass staining from adjacent building materials run-off, e.g. alkaline materials such as concrete or mortar.

 • Weather tightness, including flashings, primary and secondary seals, and weep systems.

 • The nominal position of the structure at the points where anchors will attach is dependent upon the following:

 • Deflection under construction-applied loads, i.e., material stockpiling, equipment, material handling devices, etc.

 • Deflection under dead, live, wind and thermal loads. This is especially important where cantilevered floor slabs and structural materials subject to creep deflection are involved.

 • Differential movements from floor slab to floor slab.

 • Seismic load, drift, and movement requirements.

 • Building sway and twist.

 • Construction tolerances relating to the skeletal or support structure and mullion anchor points.

 • Movement of the building at isolation and expansion joints.

 • Consideration of the surface of materials in spandrel areas and other locations where wash-off onto the glass may cause staining, tenacious residue or chemical attack.

 • Safety-glazing, fire-rating and other requirements of the applicable building codes.

 • Americans with Disabilities Act accessibility requirements.

 • Blast-hazard mitigation.

 • Windborne debris -resistance requirements.



A. Anchors and Expansion Joints:

1. Mullion vertical expansion joints should not apply loads on the glass due to movement of the structure or the framing system.

2. Wind-load anchors must allow for free vertical expansion of the mullions without causing additional stress on the mullion, mullion connectors or anchors. Slip pads are best for this purpose; oil and grease will lose their lubricating qualities over the long term.

3. Twin-span mullions should have the dead-load anchor located as close as possible to their midpoint, thus equalizing upward and downward expansion and contraction.

4. Generally, horizontal expansion joints should be no further apart than 20 feet (6 m). Expansion should be from the center toward both ends to minimize joint movements and thereby reduce stresses on sealants and connectors.



A. Deflection of Framing:

1. Under design load, for mullions that support glass, deflection of those mullions in the direction perpendicular to the plane of the wall must satisfy code requirements, but should not exceed length of span divided by 175 (L/175) for the glass edges to be considered firmly supported. If deflection allowed by L/175 is considered excessive for specific applications, the design professional may specify less deflection.


2. Under dead load, for horizontal framing members which support glass, deflection of those members in the direction parallel to the plane of the wall should not exceed an amount which will reduce the glass bite below 75 percent of the design dimension nor an amount which would infringe upon necessary glazing clearances below. Deflection should also be limited in this direction to provide at least 1/8 inch (3 mm) minimum clearance between the member and the top of the fixed glazed panel, glass or other fixed part immediately below. The clearance between the member and an operable window or door below should be at least 1/16 inch (1.5 mm).

3. Twisting (rotation) of the horizontals due to the weight of the glass should not exceed 1o, measured between ends and center of each span.


B. Erection Tolerances:

1. Within any rectangular opening there should be no more than 1/8 inch (3 mm) difference in the measured length of the diagonals.

2. Maximum variation of mullions from plumb or horizontals from level should not exceed +/-1/8 inch (3 mm) in 12 feet (3.6 m) or +/-1/4 inch (6 mm) in any single run.

3. Framing systems which are designed to have the glazing legs of the horizontal and vertical members in the same plane should have a maximum out-of-plane offset of 1/32 inch (0.8 mm) at the frame corners to avoid unequal stresses on the glass.

4. Some framing systems have a designed offset at the corner joinery and employ two thicknesses of glazing material to compensate for the offset. It is important that the dimensional tolerances of the framing offset and the glass and glazing material be determined and stated. The uncontrolled accumulation of the plus or minus tolerances may cause unequal stresses on the glass.

5. To assure that the stated tolerances for items 3 and 4 above are not exceeded in the erected framing, a simple, low-cost set of go/no-go gauges can generally be made for use by the framing erector.


C. Adjacent Work by Others:

1. Walls, column covers, knee-walls and similar construction should not be attached directly to the metal framing in a manner that will impede expansion, contraction and deflection of metal framing or add an undesigned weight to the anchors. Flexible connections can be designed to accomplish the desired purpose.

2. Attachments should never be to the wet area of a system.


D. Drainage:

1. A weep system must be adequate to drain all infiltrated water quickly. The edges of insulating laminated or wired glass, or glass opacified with an adhered polyester film or silicone coating, should not be exposed to water or moisture vapor for an extended period of time. Extended exposure to water or moisture vapor may lead to seal failure of the insulating glass unit, delamination of the laminated glass, glass-clad polycarbonate or laminated plastics, rusting of the wired glass, delamination of the opacifier film and contribute to potential attack on the coated glass surface.


2. The specific size and location of weep holes and/or weep slots vary with different glazing applications. The drainage system must ensure that water does not puddle as a result of deflection of the horizontal/sill member or blockage of water flow. The size and location of weeps must be planned to allow for prompt drainage. Good glazing practice for drainage provides a minimum of one 5/16 inch (8 mm) hole located at the center of the horizontal/sill member and/or one 5/16 inch (8 mm) diameter hole, or equivalent slot, near each end. Some glazing systems require one weep hole or slot on each end only, due to air infiltration concerns. Use of holes less than 5/16 inch (8 mm) in diameter can result in capillary action and prevent proper drainage. The glazing system supplier and glass fabricator should be consulted for specific recommendations on system drainage.

3. Some framing systems utilize the vertical mullions as downspouts to drain all infiltrated water to the lowest point before weeping it to the exterior. When these framing systems are used on multi-story applications, the system manufacturer should approve the application. The system should provide water drainage to the exterior at a minimum of one location per length of the vertical mullion. It is important that water not be allowed to accumulate on the top of, or run down, the edges of insulating, laminated or wired glass in these systems. Proper application and utilization of water deflectors is required to prevent water settling on glass units. Such conditions will lead to product failure as discussed above.


4. In order to reduce the potential for leakage, whenever possible, it is best to avoid fastener penetration through the horizontal base of any water- diverting element, including glazing pockets and flashings.


E. Glass Clearance, Blocking and Bite:

1. Glass, cushioned by resilient materials, must be free to “float in the opening” (i.e., it should have adequate clearance around all edges and laterally) so it does not directly touch the framing system. See table below for typical clearances. Large lites of heat-treated glass and laminated glazing materials may require extra face clearance due to edge bow and warp (See ASTM C 1048, C 1172 and C 1349 for tolerances).



Table 1: Recommended Minimum

Face & Edge Clearance & Glazing Bite


2. Glass should be set on two identical neoprene, EPDM, silicone or other compatible elastomeric setting blocks having a Shore A Durometer hardness of 85+/- 5. The preferred location is at the quarter points of the sill supporting frame. In some cases it may be necessary and/or acceptable to move the setting blocks equally toward the corners of the lite as far as the one-eighth points. Locating the setting blocks less than six inches from the corner of the glass may introduce additional stresses to the glass and to insulating glass seals. Please contact our sales office should you require more information. See figures bellow. Also refer to paragraph A. Deflection of Framing, on page 9.



3. The proper sizing and design of the setting blocks assures full bearing of the glass on it, yet allows water passage to the weep holes. Width of setting blocks should be at least 1/8 inch (3 mm) wider than the glass thickness. For settings in lock-strip gaskets, excessive width may reduce the designed lip seal pressure; consult gasket supplier for proper setting block width. Lead setting blocks should not be used.



4. Edge blocking, or anti-walk blocking as it is frequently called, should be used on all dry glazed systems to limit lateral movement of the glass caused by horizontal expansion/contraction, building sway and creep deflection. Lack of edge blocking can permit glass-to-framing contact on one edge and deglazing on the opposite edge. The first can cause glass edge damage or breakage; the latter can permit air and water infiltration as well as changing the glazing design from four-sided to three-sided support. Side blocking positioned within the top third and bottom third (measured vertically) is recommended for narrow, tall lites.


Edge blocking should be made of neoprene, EPDM, silicone or other compatible elastomeric material. Hardness should be per manufacturer’s recommendation, usually having a 50 - 70 Shore A durometer. Blocks should be a minimum 4 inches (100 mm) long, placed in the vertical channel and sized to allow a nominal 1/8 inch (3 mm) clearance between the edge of the glass and block.



5. Edge blocking is also used to accommodate substantial building sway and/or seismic movement. Under these situations, it is important that the anticipated sway or seismic movement be identified early in the design process. This is necessary to properly design the height of the glazing legs and the bite of the glass. The allowance for movement, retainment and cushioning necessitates increased edge clearance and bite.



6. Glass must be free to “float” (move) within the glazing pocket without touching the framing while, at the same time, maintaining adequate bite under the most adverse design conditions. The web of the framing is often cushioned near all four corners to prevent glass edge-to-framing contact, yet allowing the necessary clear space for the anticipated movement.


7. For wet glazed and structural silicone glazed systems edge blocking may not be required. Consult the window/wall system manufacturer for recommendations.


8. The designer should be aware that if glass bite is greater than typical as shown in Figure below and Table 1: Recommended Minimum Face & Edge Clearance & Glazing Bite, it may lead to high thermal-edge stresses, and the glass may require heat-treatment.



9. Glass is held in the glazing system by stops, which are sufficiently deep to retain the glass under expected loads, deflections or movements, and to cover the edge seal (sight line) of a sealed insulating glass unit.


10. Figures bellow cover the special conditions required for doors, casement, and vertically pivoted and horizontally pivoted windows. Some insulating glass fabricators may modify or void their warranty when insulating glass is “cross-blocked” as in Figure bellow (Blocking for Horizontally Pivoted Windows).

Edge blocking for casement windows and doors is a common practice and can be acceptable as long as the glass edges are not excessively loaded. Excessive pressure on the glass edge can lead to glass breakage or seal failure due to pressure points and mechanical bending stresses imposed upon the glass due to frame movement during operation. Excessive pressure on the glass edge can also impair the sealant performance if the pressure is such that the glass movement occurs in a magnitude sufficient to shear or distort the sealants. An allowable load on the edge of insulating glass being used for casement windows and doors would be that at each block the load applied shall be less than 1/2 of the total glass weight of the insulating glass unit. The design of the frames for casement windows and doors should be such that the frame is supporting the glass and the glass is not supporting the frame. The use of blocking prevents impact of the glass edges against the frame during movement of the frame supporting the glass and keeps the glass properly positioned within the glazing system. Blocking size and position for insulating glass units should follow the guidelines shown in lasted Figures


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