Well, let's assume that residental real estate has a lifespan of 30 years, and commercial real estate has a lifespan of 40 years (combined, we'll call it 33.3 years). Let's say that the utilities/roads/communications have a lifespan of 15 years. And let's also assume that there is no risk of hazard or regulations rending old buildings obsolete earlier.
Every year, you'd have 3 percent of your buildings replaced. Every year, you'd replace about 9 percent of your streets. And that's just to keep up with the natural lifespan.
But we live in a changing world. People's tastes change, prefered locations change, amentities move, neighberhoods change in value, so the real estate changes with it. It's slower to change because of the horrific transaction costs, but it changes.
And that's assuming we're not talking about cities that people actually like, where it's demand driven, and they build as fast as they can get cheap land. Assuming a population growth rate of 1 percent, and an average square foot growth of 1 percent, you're looking at 22 percent natural growth a decade, which is a lot of buildings.
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Our first challenge is to create an entire economic infrastructure, from top to bottom, out of whole cloth.
-CEO Nwabudike Morgan, "The Centauri Monopoly"
Sid Meier's Alpha Centauri (Firaxis Games)