Section 10. A city or town may adopt, in accordance with the regulations of the department, design standards applicable to projects undergoing review by the approving authority, to ensure that the physical character of development within the smart growth zoning district or starter home zoning district is complementary to adjacent buildings and structures and is consistent with the city or town's comprehensive housing plan or housing production plan, if any, and any applicable master plan or plans for the city or town. Such standards may address the scale and proportions of buildings, the alignment, the width and grade of streets and sidewalks, the type and location of infrastructure, the location of building and garage entrances, off-street parking, the protection of significant natural site features, the location and design of on-site open spaces, exterior signs and buffering in relation to adjacent properties. In a smart growth zoning district, the standards shall provide for high-density quality development consistent with the character of building types, streetscapes and other city or town features traditionally found in densely settled areas of the city or town or in the region of the city or town.

A design standard shall not be adopted if it will add unreasonable costs to residential or mixed-use developments. A design standard shall not unreasonably impair the economic feasibility of proposed projects. The department may disapprove a request for the determination of eligibility for a smart growth zoning district or starter home zoning district on account of a design standard adding such unreasonable costs or unreasonably impairing such feasibility.