Certainly, if your house is covered with something flammable, like a wood shake roof, then an ember just settling on your roof can start a fire. However, those roofs are rare or illegal in wildfire-prone areas around here but sometimes they are a concern. Many of the very old homes burned down in the terrible Oakland Hills fire in Oakland, California were covered with wood shake shingles. My roof is concrete tile. Many others are that orange-ish barrel-shaped clay tile that you see so often in California.

But, once your roof is taken care of, it's those embers drifting up under the eaves or inside the attic that will most likely burn your house down.

Direct radiant heat is also an ignition source once homes in dense neighborhoods start to burn. Unlike the more isolated homes where you can have hundreds of feet of defensible space between your house and anything flammable, your neighbor's burning house could be mere feet away from yours.