Mayor Jim Kenney’s administration took a victory lap with developers and labor unions Tuesday afternoon to celebrate a seemingly esoteric policy: an update to the plumbing and fire codes.

But the change in small print comes with big implications.

The most significant of the code reforms passed into law makes it easier to use plastic piping in mid-to-high rise residential buildings, easing construction costs that are among the highest in the nation, according to local experts. The updated code goes into effect Oct. 1.

Previously, city code required costlier cast iron and copper piping in any building taller than three stories.

The Building Industry Association (BIA), which negotiated on behalf of development interests, has said the move to plastic pipes could reduce project costs by as much as 20%.

“In addition to advancing public safety, code reform eliminates the competitive disadvantage in construction that exists when local governments use archaic and obsolete rules for buildings,” said Dave Perri, Philadelphia’s commissioner of Licenses and Inspections. “The entire supply chain of the design and construction industry becomes disrupted and inefficient when codes are not kept current.”

Philadelphia is one of only a handful of large American cities, mostly in the Northeast, that still require extensive use of expensive, heavy metal piping.

For years, the development industry and the building trades unions clashed over the city’ s plumbing code, which critics claimed remained trapped in the past because metal piping guarantees more work hours for union members.

Organized labor argued that developers were merely trying to save money by using cheaper and less effective materials.

Kenney convened the Plumbing Advisory Board in 2017 to bring various factions to the table and hammer out a compromise.

Under the new plumbing code signed into law Tuesday, plastic piping can now be used in residential buildings up to 75 feet, or about five or six stories. In high-rise residential buildings up to 150 feet, plastic piping can be used for water supply. Metal pipes are still required for sanitation in residential buildings over 150 feet, and in all commercial buildings.

In addition to cost savings on labor and materials, residential builders also hope to save on security and repair costs because copper piping often proves a tempting target for thieves.

Proponents of plastic piping argue that it is more environmentally friendly to manufacture than metal piping, and that it leaks less. The new code will also allow non-potable water systems that recirculate tap water or rainwater and also waterless urinals.

“This modernization is important because it is energy efficient, it looks at water conservation and a green code,” said Councilperson Maria Quiñones-Sánchez, the chair of City Council’s committee on Licenses and Inspections.

Quiñones-Sánchez’s relations with Philadelphia building trades unions have historically been fraught, but the president of Plumbers Local 690, John Kane, took time out of his speech to praise the councilmember for her leadership.

“She stuck with us, stuck by our side, worked with us,” said Kane. “I’m telling you in the plumbing history, this is a historical moment, this plumbing code will last decades around here.”

The bill signing dissolved into a love fest for all involved, as these kind of functions tend to. But Commissioner Perri stayed front and center throughout, emceeing the event, and winning praise from the unions, developers, and Kenney. The critical city department has dealt with its fair share of scandals over the years, but Perri has led without incident and proven to be one of the mayor’s most popular appointees.

“L&I used to be a department we were always worried — there was always something happening and most of the time it wasn’t good,” said Kenney. “But since he agreed to serve as L&I commissioner, I don’t worry about that department anymore. It’s a stellar department now.”