Windows are one of the weakest parts of building with regard to fire safety. When a fire arrives, windows usually fail before the building ignites. Broken windows then provide a path for fire to reach the interior of the building and burn the building from the inside.
Over 90% of homes lost to wildfire are caused by embers. They enter through open windows and through vents. If embers enter the house through broken windows the results could be catastrophic. But, the jet mister and automatic control valve protect the house. They were developed to safeguard the window glass from breaking, and to prevent the embers from entering the house through a broken window.
One study reports that 2 out of 3 homes destroyed by fire were destroyed by wind-dispersed burning embers or from glowing embers. Flying embers can destroy a home up to a mile from the wildfire.
Studies show that 10 to 20 minutes of window protection is usually sufficient to allow a house to survive most fires.
A window that is exposed to flames may break after only 1, 2 or 3 minutes of exposure to intense heat or to flames.
Single pane windows, and even single pane tempered glass windows, are highly vulnerable to breakage when exposed to wildfire conditions.
The extreme heat of a wildfire causes window glass to breaks. The temperature differences between the glass of a protected window and that of an unprotected window is significant. Windows protected by a jet mister remain cooled by the water mist.
Large windows exposed to fire break easily. They have a larger perimeter as compared to smaller windows. Window cracks develop and propagate inward which make larger windows more vulnerable to ember entry. Because large windows are heavier, there is just too much weight to keep the fractured glass in place. So protect your large windows with jet misters.
Tempered glass is 4 times stronger than regular glass, and is more resistant to heat. Yet an extended wildfire can break through even tempered glass windows.
The best plan is to use duel pane windows with at least one pane of tempered glass. Window screens and low-e glass are more expensive than regular windows, but they may help. shutters or shades are the best protection from wildfire.
Bowditch et al (2006) reported that laminated glass did not perform any better than annealed glass against radiant heat exposure.
McArther (1991) tested wood and aluminum framed windows and reported that the glass was the most vulnerable component of the window. During one test, the window frame failed, allowing the glass to fall out.
PVC frames are easily deformed when exposed to heat. Gaps can easily form, and then the glass pane falls out. PVC covered aluminum frames are very resilient to heat, and so these are a good choice.
Resources for window studies in firestorms are the University of California Homeowner’s Wildfire Mitigation Guide, and the manual called Fire-Safe Marin.
embershielding@gmail.com