US roofs are commonly built to deal with snow loads of ~50 pounds per square foot. I don't think it's gonna be a big deal to support tile using the same techniques (it would just need to be accounted for).
50 lbs/ft2 is pretty much the upper limit in the continental US. Most of the Midwest is around 20lb. Maine and Alaska go significantly higher. Pretty much the entire South is 10lb or less.
I've lived various places in the US. With the exception of one older house, the roof trusses were a joke: so-called 2x4's (really much thinner than that), widely spaced, held together with a few nails and little or no cross-bracing. They might theoretically hold up to the weights listed, but I sure wouldn't stand under them during a test.
Where I am now, in Europe, the roof trusses are roughly 6"x10" laminated timber. That will hold a snow load.
I was talking about the techniques being up to the task. What you observed in houses not built to handle higher loads doesn't really inform that question.
Snow doesn't matter. Rafters designed for a cheap roof plus snow need to be stronger to support slate or tile plus snow. It's a static addition to whatever else.
I've lived various places in the US. With the exception of one older house, the roof trusses were a joke: so-called 2x4's (really much thinner than that), widely spaced, held together with a few nails and little or no cross-bracing. They might theoretically hold up to the weights listed, but I sure wouldn't stand under them during a test.
Where I am now, in Europe, the roof trusses are roughly 6"x10" laminated timber. That will hold a snow load.