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Wikipedia says that semi-detached is the official term even in US English

It's certainly possible that it's an official term in some government administration office somewhere, but, if it's not clear from this thread, it's definitely not in common colloquial use.

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it's perfectly possible to demolish one of a pair of semi-detached houses.

I cannot imagine such a situation in the US, independently owned or not.
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Bitt Faulk