Fertility Rates by Housing Type

US total fertility by housing type, from the 2021 Community Survey:

Single-Family Home
   2.12   Trailer
   1.95   Single-family detached house
   1.93   Single-family townhouse
Apartment building
   1.74   2 units
   1.80   3-4 units
   1.53   5-9 units
   1.52   10-19 units
   1.39   20-49 units
   1.33   50+ units

This was proposed as a partial explanation for the very low fertility rates in places like Seoul and Bangkok, where most people live in large apartment buildings. Since much of South Korea has very low population density, people could in theory spread out, but of course that has other costs.

But what South Korea and Taiwan obviously need is lots of trailer parks.

And this, from the same source: "Unplanned childlessness is now far more common than unplanned pregnancy!"