New Normal of China’s Fertility, New Commonsense for Urban Construction

Starting with a Mathematical Problem

Population change can be simplified into a basic math problem: imagine a pool with water flowing in and out simultaneously. If the outflow exceeds the inflow, the water level drops; if the inflow is greater, the level rises.

To keep the “population pool” stable, the Total Fertility Rate (TFR) must reach 2.1. This means each couple should have an average of two children to replace themselves, with a small margin to offset “outflow” caused by natural disasters or accidents.

When we translate this math into reality, it implies that three-child families must become the absolute mainstream.

If one family has only two children, another must have four.
If one household remains childless, another must have six children to maintain a TFR of 2.1.

It must be emphasized that this only achieves zero population growth. If we want the population to grow, four-child families would need to become the norm. Looking at today’s economic and cultural environment, a society where three-child families are the mainstream is already difficult to imagine, let alone four.

Real Estate’s Impact on Fertility: Beyond Housing Prices

It is obvious that multi-child families require more space. However, in our finely partitioned urban spaces, every inch must be purchased, and most of these spaces lack effective scalability.

While real estate advertisements often use grand terms like “heirloom” or “legacy,” a high-rise apartment is essentially a commodity designed to serve specific demographic groups with specific purchasing power during a particular life stage. Thus, the need to “upgrade” houses is a deliberate byproduct of the current urban development model.

For instance, in the customer segmentation data of Vanke (a leading developer), we see a rigid correspondence between a family’s life cycle, age, purchasing power, floor plan, and urban resources.

City Centers: Planned as high-end business residences with the highest prices; units are small and unsuitable for large families.
Peripheral Areas: Young people, who rely most on urban amenities and public transport, are allocated smaller units in remote locations to match their limited purchasing power.

During the peak of China’s real estate boom, Vanke consistently ranked in the top three for sales. This means the methodology represented by Vanke has profoundly shaped the cities we see today. However, when viewed through the lens of a “Fertility-Friendly City,” this “industrial success” reveals a darker side.

Cities for the Three-Child Era Built on One-Child Models

Data shows that China’s total urban built-up area grew from 51,238.66 km² in 1995 to 198,602.14 km² in 2018—an increase of 287.60%.

Throughout this massive construction process, the “one-child” family model was the absolute mainstream for planning. This preset assumption of the “mainstream family structure” affects every aspect of urban construction:

Urban density settings and per capita green space algorithms.
The scale of community kindergartens.
The functional design of kitchens, children’s rooms, bathrooms, and storage spaces.

In 2006, the Ministry of Construction issued the famous “70/90 Policy,” requiring that at least 70% of the total housing area in new projects consist of units smaller than 90 m². While intended to curb rising prices and serve the influx of migrants, it resulted in higher building densities and extremely compact layouts. A flood of 89 $m^2$ three-bedroom units emerged.

Regardless of personal desire, the design capacity of living spaces effectively sets a “hard ceiling” on the urban population.

Conflict Between Living Spaces and Child-rearing Models

Many Chinese families rely heavily on grandparents for childcare. This is due to the inability of a single income to cover household expenses, the continuation of agrarian traditions, and the lack of an affordable public childcare system.

Thus, a family’s fertility often depends on how many children the grandparents are willing or able to care for. However, living together in compact urban spaces is often an unpleasant experience:

Social Isolation: Grandparents moving from other cities lose their social networks and enter a “zero-social” life in a strange environment.
Physical Barriers: As physical strength declines, the elderly are limited to a walking radius. In new districts squeezed by high prices, wide expressways and overpasses make “walkable life” with a child difficult.
Space Compression: Compared to a courtyard in the countryside, they may only get one small room in the city, often without a private bathroom. Friction over lifestyle habits becomes frequent in such tight quarters.

Eventually, many grandparents feel their efforts are unappreciated. Beyond family dynamics, the tension of physical space plays a critical role.

The Clash: Upgrading Cycles vs. Biological Cycles

The ideal biological window for fertility is between ages 20 and 35. To have three or more children, it is best to complete the process during this stage.

However, young people in this stage have just entered the workforce. Without family support, they cannot afford homes. The market offers them small units in underdeveloped areas, increasing the time and money spent on child-rearing. By the time they accumulate enough wealth to “upgrade” to a better space, their biological fertility window is closing.

The current development model forces fertility to depend on “purchasing power clearing the way.” Each additional child brings a nonlinear increase in housing and rearing costs. If a family cannot upgrade their home due to income stagnation, they often give up on having more children.

In short: smaller houses, fewer children.

Homogenization and Social Ecological Constraints

When 70% of houses in an entire district are under 90 m², the result is social ecological homogenization.

Initially, young people move in together, causing concentrated traffic congestion. They give up births at the same time, causing childcare consumption to surge and then rapidly decline.

Unless these residents can “upgrade” and move out in a synchronized fashion to make room for the next generation of youth, these communities will inevitably suffer from “tidal phenomena” caused by an over-concentration of specific life cycles. Most high-rise units cannot meet the needs of life-cycle replacement.

New Normal, New Commonsense

People are the foundation of the city, and population structure is the foundation of real estate. In the context of “low fertility,” “aging,” and the push for “Fertility-Friendly Cities,” urban construction requires a fundamental update of its underlying logic.