Legislation that would define a green roof and establish zoning height allowances for rooftop gardens was considered and postponed until March 30 at a city Planning Commission hearing Tuesday.

Councilman William Peduto's legislation would define green roofs as "regular and customary accessories" to homes and commercial properties. The city has approved green roofs in the past but now can better regulate the results, said planner Corey Layman.

He said the Bureau of Building Inspection assured him that existing code covers standards regarding the structural integrity necessary for green roof installations.

The height of plants allowable would fall under existing height restrictions for the zoning district, he said.

One concern among some commissioners was that a rooftop garden could become a weed nuisance for neighbors and another enforcement demand for the Bureau of Building Inspection.

Dan Gilman, Mr. Peduto's chief of staff, said people who install green roofs go to "significant expense. The thought that someone would put it up there" only to let it grow out of control is unlikely. Depending on the technology used, the structural analysis required and the intensity of the plantings, the cost of a green roof is estimated at $8 to $25 a square foot.

The issue was postponed because commission members wanted some wording changes and clarifications about enforcement.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.