Quick answer
No, there’s no legal requirement in Ohio mandating special insurance once a home crosses $1 million in value. What actually happens is market-driven, not regulatory: many standard and captive carriers cap dwelling coverage well below that threshold, or decline to write it at all past a certain value, simply because their underwriting formulas weren’t built for it.
In practice, this means a $1 million-plus Ohio home often needs a specialist carrier not because the law requires it, but because the standard market won’t properly price it. The number that actually matters isn’t a legal threshold, it’s your home’s real rebuild cost against what a given carrier is willing and able to insure accurately.