No, you’d remark that your house has appreciated in value over the past 20 years. But you wouldn’t have realized any of that gain until you sold the house - the point being that the realization is the actual taxable event, which is why it matters from the pedantic technical accounting POV. The fact that you turned around and bought another house just means you’re doing something new with your realized gains. Now you have a new cost basis. Maybe that’s what you’re saying with “unrealized gain” though.