Council: GPC - Glass Products Council

The following chart lists the industry standards and specifications that apply to glass used in windows, doors, skylights and architectural glazing applications. It is intended for reference and guidance only and should not be used to assess the suitability of specific installed glass/glazing. Concerns regarding specific glass characteristics should be evaluated by a professional having expertise in the glass/glazing field using the appropriate specification(s).

Glass Inspection for the Homeowner provides guidance addressing the general criteria and requirements for inspecting glass/glazing installed in windows, doors and glazed assemblies.

The glass industry has developed consensus standards/specifications that address quality aspects of various types of glass used in windows, doors and skylights. These standards are very comprehensive and typically written for manufacturers who have expertise in applying them. The standards are also very specific to a given glass type. These types include raw flat (annealed) glass, heat-treated glass (ex. tempered), coated glass (ex. low-E), laminated glass and IGUs. Unfortunately, the methods of inspection and the blemish or issue criteria are not always the same for each type of glass.

In most cases, a homeowner will have a window, door or skylight that contains an IGU that is comprised of two or more panes of flat glass. Typically, this glass will also have some type of low-E coating. If there is a safety concern or a code requirement for safety glazing, the window may also contain tempered or laminated glass. With a combination of all these glass types in one window, door or skylight, sorting out the appropriate criteria to the respective standard is at best a complicated, if not confusing, endeavor. How then is a homeowner to know whether an issue or blemish is a legitimate concern?

The following is a general guideline offered to simplify the inspection of glass issues for the homeowner. This is not necessarily a definitive guide covering all glass related concerns; that’s the job of the industry standards. Rather, this guideline is a check for a homeowner to flag whether an issue merits consideration for replacement.

Home Inspection Directions

1. Thoroughly clean the glass on both sides with glass cleaner.
2. Stand 10 feet away, directly in front of the glass (90° to the surface).
3. The glass should be illuminated with daylight, but not direct sun.
4. If an issue or blemish is readily apparent, measure the size of the blemish.
5. Contact the manufacturer if the blemish is noticeable and is outside the following limits.

Blemishes

Other Issues

Types of Glass

Glass is used to provide light and allow a view from either side to the other side. It can be clear, coated, tinted and insulating. Several types of glass may be used in windows, doors and skylights throughout North America. Standards concerning the manufacture of basic glass are covered in other documents. Below are definitions for common glass types.

Annealed

“Annealed glass” is basic glass manufactured using the standard float glass process. All glass made for windows, doors and skylights in North America is manufactured by the annealed process. This is also known as annealed glass unless it is subsequently heat treated.

Heat-Treated: Tempered and Heat Strengthened

“Heat-treated glass” is glass that has been pre-stressed by heating followed by sudden cooling to give it two to four times the strength of ordinary annealed glass. There are two main types of heat-treated glass: heat- strengthened and tempered glass. Tempered glass is also known as toughened glass. When it breaks, it breaks into small pieces. Tempered glass may be used as a safety glazing product; however, heat-strengthened or annealed glass may not be used as a safety glazing product without laminating.

Laminated

Certification mark for laminated glass example

“Laminated glass” is an assembly consisting of two or more layers of one of the above glass types with an interlayer material bonded between. In many cases, laminated glass may be used as a safety glazing product, provided it meets applicable requirements. Laminated safety glass will have an etch or mark similar to that shown below, indicating compliance to ANSI Z97.1.

Wired

“Wired glass” is glass that includes an embedded wire mesh. It is primarily used in fire-rated products and is not to be used as a safety glazing product. Its use has diminished greatly in residential buildings, and it is not recommended for use in areas where the potential exists for human impact.

Insulating Glass Unit (IGU)

An insulating glass unit or IGU is two or more panes of glass spaced apart and sealed to form a single assembly with an air- or gas-filled (such as argon) cavity between panes. IGUs are manufactured with a variety of glass types and thicknesses. Heat strengthened, tempered or laminated glass may also be used as part of the construction. Most IGUs are manufactured with the same thickness of glass used on all panes, but other product types and special applications such as sound control, overhead glass or security may necessitate the panes being of different types and/or thicknesses.

Surfaces of a double pane IGU (image courtesy of IGMA)

For ease of description, the surfaces of a double pane IGU are numbered according to the following convention: surface 1 (surface facing outside), surface 2 (inside surface of outside pane), surface 3 (outside surface of inside pane) and surface 4 (room side surface). Applying the same numbering sequence to a triple pane IGU results in surfaces 1 through 6, a four-pane IGU results in surfaces 1 through 8.

Glass panes in an IGU are separated by a “spacer” that maintains the gap between the panes. Historically, spacers have typically been made of aluminum. To reduce heat transfer through the edge of the IGU and increase overall thermal performance and condensation resistance, a spacer constructed of materials that are less thermally conductive may be beneficial.

Example of an IGU spacer containing desiccant

Typically, spacers contain desiccant to remove moisture within the IGU cavity. Desiccants lower the moisture dew point within the cavity, which reduces the potential for the formation of condensation inside the IGU.

The construction of an IGU is based on the edge seal system (sealant, desiccant and spacer) used to hold the IGU together and to seal to its supporting elements. The edge seal system serves five principle functions:

1. Maintain gap between the panes
2. Remove moisture from between the panes to limit internal condensation
3. Prevent moisture from penetrating space
4. Retain gas fills within the space
5. Maintain seal around the IG perimeter

Use of Tinted Glass

While clear glass is the most common glass component of IGUs, tinted glass may be used to reduce glare, reduce solar heat gain or as an architectural feature. The most common tints used are bronze, gray and green. The degree of tint depends on both the composition and thickness of the glass pane. Tinted glass is usually placed on the outboard pane of the IGU. It may require heat treatment to reduce potential stress and breakage due to absorbed heat.

Use of Applied Films

Glass performance can be altered through the use of films applied to one or more surfaces of glass or the IGU.

Films that are applied after the glass is installed (“aftermarket” products) are typically made of polyester and, in some cases, may give the glass a reflective appearance or a one-way mirror effect. These films may be intended to reduce fading of fabrics on furniture, improve sound insulation, improve glare control or, in some instances, improve safety in case of glass breakage. However, there are usually unknown or unintended side effects that can reduce the product’s performance in other ways, shorten its useful life and negatively affect appearance.

Aftermarket applied film standards do not exist at this time and use of these films may void warranties provided by the window, door, skylight or IGU manufacturer. Before applying such films, homeowners are advised to read the care and maintenance instructions along with the warranty of the film and the window, door, skylight or IGU manufacturer.

Low-E Glass Coatings

Another use of films or coatings in IGU technologies is low-E glass. There are two types of low-E coatings available: “hard coat” or pyrolytic and “soft coat” or sputtered. 

Low-E glass has one or more metal coatings applied to the glass, used to reflect thermal radiation or inhibit its transmission thus reducing heat transfer through the glass. There are many different low-E coatings, each one tuned to allow for certain spectrums of light and energy to pass through them thus providing different thermal performances to meet the needs of different climates.

An alternative IGU construction incorporates low-E plastic films that are suspended within the IGU. Instead of internal glass panes, these films are suspended through attachment to the spacer system. They offer the opportunity to incorporate high-performance low-E coatings without the additional weight and overall thickness typical of traditional triple pane or four pane IGUs. Visual irregularities may occur if the plastic film becomes wrinkled or disengaged from the spacer system. There are no industry standard specifications for this type of construction and the product manufacturer should be contacted to address any concerns.

AAMA GDSG-1, Glass Design for Sloped Glazing
Outlines design considerations necessary for choosing the proper glass for non-residential skylight and sloped glazing applications and describes the minimum requirements for sloped glazing as specified in the major building codes.
Purchase Document

AAMA GAG-1, Glass and Glazing
This guide is intended to better acquaint those in the construction industry with glass manufacturing processes, glass types and strengths, wind load resistance, breakage behavior, and other mechanical and structural issues.
Purchase Document

AAMA IPCB, Standard Practice for the Installation of Windows and Doors in Commercial Building
Purchase Document

AAMA 2400, Standard Practice for Installation of Windows with a Mounting Flange in Stud Frame Construction
Purchase Document

AAMA 2410, Standard Practice for Installation of Windows with an Exterior Flush Fin Over an Existing Window Frame
Purchase Document

FMA/AAMA 100, Standard Practice for the Installation of Windows with Flanges or Mounting Fins in Wood Frame Construction
Purchase Document

AAMA 1607, Installation Guidelines for Unit Skylights
Purchase Document 

AAMA CWG-1, Installation of Aluminum Curtain Walls
Purchase Document

AAMA TIR-A1, Sound Control for Fenestration Products
Purchase Document