If the glass in a window breaks during a wildfire, fire can easily enter a home. Similarly, if a window frame ignites, it is possible that fire could burn through the frame material, and ignite other material inside a home.

ID Question Example
W1 Does the home have single pane windows? Tempered window:
  An older home will likely have single pane windows. However, single pane windows can also be tempered, which affords even better protection than windows with dual pane annealed glass. Tempered glass is stronger than 'regular' annealed glass, and will provide additional protection during a wildfire (but your window will have to be closed in order to benefit from the tempered glass). Building codes already require tempered glass in some locations (for safety reasons), so some newer windows may already have tempered glass. For example, in newer construction, windows that come within 18 inches of the floor must have tempered glass. Sliding glass doors, and other doors with windows, and windows immediately adjacent to doors, will have tempered glass. A small etched label will be present in the corner of a piece of glass in a window if it is tempered. Since it is small, it may be too small to read.

W2 Is the window or window frame in poor condition (e.g., window can't be closed, frame is warped)? Warped frame:
  Burning embers could land on a window sill, or as is shown in this photo, the sill at an entry door. The embers could then ignite debris, or ignite the decayed trim. Decayed wood (shown in this photo) ignites as a lower temperature than that required for sound wood, so is more vulnerable to an ember exposure.
W3 Are there any man-made fuels within 3' of the windows? Man-made fuels:
  Man-made fuels include construction materials, newspaper or trash, coir or wood doormats, arbor or trellis, propane tanks, combustible lawn furniture, firewood pile, gas-powered vehicle, carport or detached garage, gas-powered lawn tools, flammable bins or cans, outbuildings, and other structures.
W4 Is there any vegetation within 6' of the windows? Vegetation near window:
  Not all plants are strictly ‘good’ or ‘bad’. The size, location, structure, and condition of vegetation determine its risk to a home. Plants closer to a home are a greater risk to a structure. Any plants near a house should be pruned, regularly watered (preferably by being on a drip irrigation system) and any dead material removed, including at vegetative debris at the soil level. Along with these precautions, don’t use bark or other combustible natural materials as plant bedding. Embers can land in this, smolder, and later go into flaming combustion. In addition, the smaller the better, especially close to combustible siding, under a window, or inside a corner. Better yet, consider using noncombustible ground cover next to combustible siding or near windows, regardless of siding type.

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