Present Evan Mast's empirical evidence on how market-rate housing construction filters through the rental market to benefit low-income households, and its implications for San Francisco housing policy.

E. S. cities, their previous addresses, the current residents of those addresses, and so on, creating chains of moves. These chains are combined with a simulation model to estimate how many residents leave lower-income neighborhoods per 100 new market-rate units built.

Mast's analysis demonstrates strong migratory connections between new market-rate construction and low-income neighborhoods: new buildings attract residents who vacate units elsewhere, and those vacancies cascade down the income distribution.

Building 100 new market-rate units leads an estimated 45-70 people to move out of below-median income tracts and 17-39 people out of bottom-quintile income tracts, with almost all of the effect occurring within five years.

This contradicts the common assumption that market-rate construction only serves high earners: it reduces demand pressure and loosens the housing market in low- and middle-income areas even in the short run.

For San Francisco, the implication is direct: each approved market-rate project frees up existing units that lower-income households can access, and blocking such construction slows this relief valve.