The high-rise apartments — some with panoramic views of Singapore’s tropical cityscape — are airy, light-filled and spacious enough to comfortably raise a family. They are also public housing units, and for decades, were emphatically affordable, giving Singapore an enviable rate of homeownership.

Now, however, at least a few of the apartments are being sold at a price that would have been unthinkable not long ago: more than $1 million.

“I’m sad to see that — because public housing must equal affordability,” said Liu Thai Ker, the urban planner who gets much of the credit for creating the country’s widely lauded approach to housing its citizens.

Now 86, Mr. Liu is considered the architect of modern Singapore because of his role overseeing the development of about half of the more than one million apartments that make up public housing in the small and exceptionally prosperous city-state of 5.6 million people.

But in the 1960s, the country’s economic standing was starkly different. It was one of the poorest cities in Southeast Asia, where three out of four residents lived in overcrowded and filthy slums, in ramshackle houses with tin walls known as “squatters.”