AMHERST — After continued appeals from members of Town Meeting to encourage more affordable housing be included in large-scale housing developments, the Planning Board is bringing forward its own version of changes to Amherst’s inclusionary bylaw.

Under the proposal that will come before Town Meeting next week, any housing project with 10 or more homes or apartments requiring any type of special permit from the Planning Board will be mandated to set aside a portion of the units for low- and moderate-income families.

Planning Board Chairman Stephen Schreiber told the Select Board Monday that this zoning amendment will acknowledge, for the first time, that all special permits issued can be used to trigger construction of affordable housing.

In the past, Schreiber said, this has been part of a “contested landscape.”

Town counsel Kopelman and Paige informed planners that Article 15 of the town zoning bylaw, adopted in 2005, is only valid when a special permit is issued for use of a property, and not when it is issued related to circumventing dimensional regulations, such as the height of a building or lot coverage.

But this has meant that projects that have received special permits for dimensions, such as the previously built Kendrick Place and Boltwood Place, and the under-construction One East Pleasant at the former site of the Amherst Carriage Shops, have not been required to include any affordable housing.

Twice in recent years, including in June, Town Meeting has considered citizen petitions that would have required developers to provide affordable units whenever any special permit was issued. Town Meeting supported this most recent measure 110-61, falling eight votes short of the two-thirds majority needed to change town zoning.

Under the new proposal, which the Select Board is unanimously endorsing, the Planning Board would create a calculation for affordable units that counts how much of the new building is attributable to the special permit related to the dimensions.

Select Board member James Wald said he has always supported town counsel’s interpretation of the bylaw, but that he has also been concerned that in-fill developments downtown don’t have a mix of people with varying income levels.

“I think this looks like an interesting way to get around that dilemma,” Wald said.

Amherst Business Improvement District Executive Director Sarah la Cour said she would support the measure, but that it would add complexity to any new project and might discourage developers.

Embedding the way the calculation is done in the Planning Board’s rules and regulations, and not in the town zoning bylaw, is also problematic, she said.

“There’s so much room for interpretation in this,” la Cour said.

The Amherst Area Chamber of Commerce expressed similar concerns in a memo from its executive director Timothy O’Brien, observing that the proposal “adds a layer of regulation that may prove daunting to developers in the future and lead to their simply bypassing Amherst as a desirable site.”

Economic Development Director Geoffrey Kravitz said there is already concern about added costs whenever requiring affordable units from developers. Having the calculation in the board’s rules and regulations may mean less stability on how this is done, making it harder to attract out-of-town developers.

“It adds uncertainty,” Kravitz said.

Scott Merzbach can be reached at smerzbach@gazettenet.com