Inclusionary zoning

Inclusionary zoning ties the production of below-market housing to the production of market-rate housing. A typical ordinance sets a percentage of units in a new building that must be affordable to households at a stated share of area median income, for a set number of years. Some programs are mandatory; others are voluntary and offer a density bonus, reduced parking, expedited approval, or a tax break as the inducement. Many allow a fee paid in lieu of building the units.

The economics are straightforward to describe and contested to evaluate. The restricted units cost the same to build as market units but produce less income, so the building's total net operating income falls relative to an all-market building of the same cost. Something has to absorb that gap: higher rents on the market units, a lower price paid for land, a smaller developer return, or an offsetting benefit like added density that spreads costs across more units.

Assume a 100-unit building requires $2,154 per unit per month to work, and an ordinance requires 10 units to rent at $1,200. The lost income is 10 × ($2,154 − $1,200) × 12 = $114,480 per year. Spread across the 90 market units, market rents would need to rise by about $106 per unit per month to restore the same gross rent, if nothing else changed. In practice, some of that lands on the land price instead, and a density bonus can offset part of it.

Whether the requirement suppresses overall construction depends on how large it is relative to the offsets, and on whether the local market can bear the higher market rents. We treat it as a trade-off to be measured, not a verdict, and cover the mechanics in Affordable Housing and Zoning.