SOUTH KINGSTOWN -- The Planning Board adopted the final piece needed to implement zoning regulations that would require subdivision developers to include affordable housing in their projects.

In the past six months, the Town Council and the Planning Board approved "inclusionary zoning" regulations mandating that 20 percent of all subdivisions of six or more lots be affordable to people of low or moderate income. At least 4 units in a 20-unit project must meet those criteria.

In exchange, the developers will be granted density bonuses to offset the cost of building the affordable units. The regulations apply to all major land development projects, including condominiums and housing complexes for the elderly. All housing created under the regulations would have to remain affordable for at least 99 years.

In the latest phase, the Planning Board on Sept. 12 updated the town's subdivision regulations to reflect the new rules. The board found that the measures were consistent with the town's goals of increasing the low-to moderate-income housing in town.

The state has mandated that 10 percent of all housing in each town meet the state's criteria for affordable housing by 2025. Currently, 5.2 percent of South Kingstown's housing is classified as affordable. An additional 459 units would be needed.

The town's affordable-housing plan identified inclusionary zoning as a key strategy in achieving the 10-percent goal. The aim is to ensure that the community remains diverse, with a range of housing options for those on assistance or having trouble affording rents or purchasing a home and those in the local work force.

The building industry has criticized inclusionary zoning -- now being weighed in communities throughout the state -- as unfairly burdening new homebuyers and builders with the cost and burden of solving the state's affordable-housing crisis.

South Kingstown's regulations took effect upon their passage, planning officials said.