PROVIDENCE — Developers received a boost Thursday as a key bill expanding development of open space was approved unanimously by the House Committee on Municipal Government.

H5703, known as the “slopes bill,” prohibits cities and towns from excluding sloped land when calculating a buildable lot. Some municipalities, particularly those with rural areas, relied on the calculation to maximize open space to protect water quality and wetlands, opponents of the bill said. A single-state standard also potentially impedes state and community efforts to implement long-term plans to manage growth with concepts like village centers and transportation-oriented development.

But developers say it’s unfair to exclude slopes, which can’t be built on, from calculating residential lot sizes. “Slope is the most misunderstood thing I’ve seen in a while,” said Robert Baldwin, a home builder from Lincoln and past president of the Rhode Island Builders Association.

Baldwin said he’s had to turn down offers to invest in subdivision projects in large open areas because local slope ordinances significantly shrank the number of lots.

The bill is opposed by environmental groups, land trusts and municipalities, which see the legislation as imposing a statewide standard on communities with diverse land issues. Similar legislation that allowed slopes and wetlands to be including in calculating lot sizes stalled in committee during the last two years.

“It’s an erroneous assumption that these bills are going to help the Rhode Island economy. It’s not true,” said Paul Roselli of the Burrilleville Land Trust after the hearing. Roselli testifies regularly on behalf of 15 municipalities and more than 20 other land trusts and environmental groups at the hearings.

The following municipalities subtract slope when determining land for development: Charlestown, Coventry, Cranston, Cumberland, Glocester, Hopkinton, Johnston, Lincoln, North Kingstown, North Smithfield, Richmond, Tiverton, Warren, West Greenwich and Westerly.

Roselli said the legislation is intended to appease a few influential developers. Builders, he said, that prospered during the last economic upturn despite the slope and wetland restrictions imposed by municipalities. “They were around during the boom times, and the 15 towns are pretty towns they are desirable places to live where the water quality is good and the sense of place is still intact.”

Several Rhode Island builders groups advocated for the slopes bill, as well as separate legislation allowing wetlands in calculating lot sizes. “We’re not trying to hurt the environment,” John Marcantonio, director of the Rhode Island Builders Association, said after the hearing.

A Senate version of the bill (S544) is under consideration by the Senate Judiciary Committee. The House Judiciary Committee will hold a hearing on the wetland setback bill May 8.