Table 9.15.3.4
Minimum column pad in Canada is .4 square meters (620 sq. in.), unless engineering is provided and I have not had anyone go that route, even engineers designs for their own homes (they have a tendency to go a little overboard). I've only seen 18" concrete tubes used in commercial construction. Even there, we see them on large formed footings. When I say I've never seen someone use a sonotube without a column pad under it, I mean anywhere. Commercial, residential, it doesn't matter. I've never seen it.
Most people will use a 8-10" dia. tube for a residential deck here to reduce the cost of concrete.