none of the roofs are rated to carry that. All the planted crops, except trees, are killed. All trees less than a few meters die, naturally. You can't plow it. Most plants won't grow in it. Cars won't run for very long when it's in the air and nobody's digging a car out of a few meters of ash without patience, and if you did there's no where to drive it where you won't get bogged down in soft crunchy ash. The ash is suffused with toxic gases, some of which precipitate as acids. When it rains it kills all the life in all the rivers, and the silt changes the course of major rivers and minor streams. When it gets to the Atlantic and the Gulf it kills almost all of the fish in the ocean. It interferes with cell phone reception, TV and radio. A few meters of ash is enough to clog every hydro power plant, every nuclear power plant in the country. It blocks all the railways and all the highways of course, and that's how we move food around. And if you're not directly affected but you don't like America, that would be a fine day to attack.