Wildland-Urban Interface Demonstration Building - Windows

Wildland-Urban Interface Demonstration Building
Roofing & Gutters Vents Eaves & Soffits Windows Siding Near-home

Research has shown that the glass is the most vulnerable part of a window. This is a vinyl window, with a dual pane insulated glass unit (IGU) that has tempered glass. Note that the trim surrounding this window is fiber cement trim.

Although research has shown the glass is the most important part of the window, it has also shown that an unreinforced horizontal separator in single- or double-hung vinyl windows can deform. Embers and flame can enter through the resulting gap that develops between the separator and the glass. If the separator is reinforced with a metal bar, this deformation won't develop.

This is an example of a metal enforced horizontal separator in a vinyl window (photo courtesy of Ply Gem Windows, West Sacramento, CA).

The etching shown in the corner of this window indicates that the glass has been tempered. Each piece of tempered glass will have this marking (called a “bug”).

This vertical slider is a wood window with a vinyl skin on the outside (exterior). Vinyl and metal clad wood windows reduce the needed maintenance on wood windows. Performance under wildfire scenarios is more a function of glass - this window has tempered glass. Higher performance glass is available, but at a higher cost. During wildfires, windows should be closed to reduce the potential for ember entry into the living space of the home or building.

A window with a single pane of annealed (non-tempered) glass breaks at a radiant exposure of about 10 kilowatts (kW) per square meter (m2). Two panes of annealed glass (in a dual pane insulated glass unit) will break at about 25 kW/m2. One layer of tempered glass will break at about 45 kW/m2. As a reference, human skin would burn at a radiant exposure of about 4 kW/m2. Materials ignite at exposures of 10 to 20 kW/m2. Ignition is a function of level of exposure and exposure time. Materials ignite quicker at higher radiant exposure levels.

Glass breakage data compiled from the Ignition Handbook (by V. Babrauskas) overlaid on radiant heat flux data, measured by Jack Cohen during a crown fire research project in the Northwest Territories in Canada. Glass breakage will depend on the radiant energy exposure level, and the exposure time. During this fire, the 45 KW/m2 level wasn't maintained long enough to break the glass.

Wildland-Urban Interface Demonstration Building
Roofing & Gutters Vents Eaves & Soffits Windows Siding Near-home