The Metro Council approved four expansions to the region’s urban growth boundary Thursday, opening 2,200 acres just outside four cities for development.

The regional government accepted proposals from Beaverton, Hillsboro, King City and Wilsonville that together are expected to account for 6,100 new houses and 3,100 apartments.

It’s the first expansion of the urban growth area since 2014. It’s also the largest since 2002, when 17,000 acres were added. That expansion included swaths of North Bethany, now a site of intense development, and Damascus, where residents have resisted urbanization.

This year’s urban growth decision is the first in which cities were required to submit concept plans for developing their prospective expansion areas. That’s an effort to avoid a situation like Damascus, where, without infrastructure or a city government, there’s little hope of the suburban development once imagined.

Metro estimates that over the next 30 years, more than 500,000 residents and 279,000 households will be added to the seven-county region — Clackamas, Columbia, Multnomah, Washington and Yamhill counties in Oregon and Clark and Skamania counties in Washington. That includes other urban and rural areas beyond Metro’s boundary, which is limited to parts of Multnomah, Washington and Clackamas counties.

But the 9,000 residences projected in the expansion proposals are too few to have more than a modest effect on the affordability of homes for sale, and they aren’t expected to have much effect at all on rental prices, the agency said.

Overall, Metro’s forecast calls for the vast majority of new homes to be built within the existing urban growth area, either on vacant land or through redevelopment.

Metro is next expected to weigh an urban growth boundary expansion in 2024.

-- Elliot Njus

enjus@oregonian.com; 503-294-5034; @enjus