I’ve never seen slate roofs in California, so not sure if these are to code here. We looked at metal and other materials, but the problem is the weight is different, so now you are engaging an engineer to evaluate structure, submitting plans, dealing with code updates. Or just new asphalt shingles every 15-20 years. The payoff isn’t there and folks don’t tend to keep houses for generations, unlike in the UK.
I think you may be overestimating the extent to which UK houses are held for "generations.
Because if you're trying to use building materials that the local contractors are not familiar with, you're going to have a bad time.
In order to have a better roof, you probably must have a better entire house under it also.
Where I live in Europe, roofs are usually ceramic shingles, which should easily last 50-100 years or more.
Of course, the down side of higher quality building standards is cost. Building a houses here costs a minimum of half-a-million, and quickly hits a million...
A tar roof has an unavoidable time limit on the whole thing.
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.
It sounds odd to my ear to matter-of-factly state that the US is deprived due to being capital-poor.
I mean, I'm not disputing anything specific, but where do middle-class people have better access to consumer finance than the US?
If you'd asked me what single fact represents American homeowners to people interested in economics around the world, I would've guessed it's the access to 30-year fixed rate mortgages.
As far as I know this is a deliberate policy in the US, that has not been emulated by those envious of the American economy, but why I haven't a clue.
In Europe a lot of the government fiscal crises were a result of small countries having to backstop giant cross border banks that happened to be headquartered there, and there is little appetite for tighter fiscal union.