This is a photograph taken after a 2007 southern California wildfire in the Lake Arrowhead area. The outer pane broke under radiant exposure from a neighbor’s house that had ignited and was ultimately destroyed. The window was dual pane with a vinyl frame. Both panes contained (regular) annealed glass.

Tests conducted at the University of California, and in Australia, have shown that under simulated wildland fire exposures, glass is the most vulnerable part of the window. A consumer could be largely ‘indifferent’ to frame type, and could therefore select based on other criteria (i.e., cost, energy, etc.).

Based on these tests, and others, Chapter 7A of the California Building Code allows use of any framing material. Glass in a window can comply by any one of the following ways:

The first two options for compliance (minimum dual pane with tempered glass, and glass block) are prescriptive. The California Energy Code has resulted in dual pane windows being the norm in new construction. Currently, building code requires tempered glass for windows in or immediately adjacent to doors, and in windows that are 18” or less from a floor. Chapter 7A requires one of the panes in all dual pane windows to be tempered.

The third option requires testing in a vertical furnace following a specified time-temperature regime. This test results in a largely radiant exposure. After 20 minutes, the exposure temperature would be about 1300 degrees F.

The fourth option (passing SFM standard test 12-7A-2) is a fire penetration test. During this test, a window is subjected to a flame impingement exposure.

A tempered ‘bug’ is shown in the upper left corner of the glass in this window. Incorporation tempered glass in the window is the most common way that window manufacturers are complying to Chapter 7A.

Windows that incorporate tempered glass will definitely cost more than those with annealed glass. Tempering requires an additional step in the glass making process.

The added cost will depend on:

  1. How common is the window opening (if common, then increase will be less)?
  2. Will the manufacturer decide to only provide dual-pane tempered? If yes, then increase will likely be more.

Depending on these factors, the reported added cost has been 15% and higher.

This is a photograph of a vertical furnace used to evaluate the fire performance of walls, and is used to give them their ‘hour’ rating (e.g., a 1-hour wall, a 2-hr wall). Although this designation has been used by code officials to specify wall construction (siding performance / compliance) in some wildland urban interface areas, it is predominately used to minimize fire spread from floor-to-floor and room-to-room in a single family home, unit-to-unit in multi-family construction, and home-to-home in urban fires.

Chapter 7A doesn’t currently rely on the fire resistance ratings (e.g., a one-hour wall) for siding compliance, but the [20-minute exposure] fire resistance rating test is one way for windows and doors to comply.

This is the time-temperature curve specified in ASTM E-119. This curve would also be used in the 20-minute window and door tests. The furnace temperature at the end of 20-minutes would be about 1300 degrees F.

This is a photograph of the window test assembly specified in SFM Standard 12-7A-2. The wall in the plane of the window, and the side walls are clad with gypsum wall board. A gas diffusion burner that provides the flame impingement exposure to the window is placed at the base of the wall. The burner is on for eight minutes.

In order for the window to comply, burn through the window or framing material (into what would the living space of the house) cannot occur.

An example from a SFM 12-7A-2 test showing failure by fire penetrating the window by igniting and burning through the frame material.

An example of failure by fire penetrating the window by fire breaking the glass in the window.

For most exterior building components, a current list of products that comply to Chapter 7A provisions are found in the WUI Products Handbook (click on ‘NEW PRODUCTS HANDBOOK’).

The WUI Products Handbook is published on-line by the Office of the State Fire Marshal as a pdf document. It is updated regularly.

A fee must be paid to OSFM to have a product included in this handbook. Manufacturers are not required to include their compliant products in this, or any, publication. However, this is an easy way to show compliance. Manufacturers wishing to have their product included in this book must have their product tested at an OSFM approved fire laboratory. The test report, prepared by the fire laboratory, must be submitted to OSFM for review and approval.

This is a page from the WUI Products Handbook . Information under ‘Exterior Windows (SFM 12-7A-2)’ says ‘None’, indicating no manufacturers of windows have included their product in this Handbook. To date, all window manufacturers have chosen to comply prescriptively to the Chapter 7A requirements by incorporating tempered glass in their windows.

Currently only manufacturers that comply via a performance requirement can have their products included in this Handbook.