exactly...  many of the homes in last years Ventura fire were burning ON THE INSIDE first, spreading outward.  I lived there most of my life and have been witness to numerous fires.  They start on the roofs first, nearly 100% of the time.  Look at this video and tell me if it makes sense.  Look at the firefighters not engaging ANY of the structures.  Do you know how long it takes for a house to burn down from an ember or two?  It's takes a long time to even get started, perhaps as much as 30 minutes before large flames are seen.