PORTLAND, Ore. -- Portland's exploding growth has meant a lot of old homes meeting the wrecking ball.

But numbers show a relatively new rule to discourage that, is working. In 2016, the city of Portland said that if homes built in 1916 or earlier were going to be demolished, they must be carefully deconstructed instead of just knocked down. That means they dismantle it in order to recycle or reuse 90 percent of the materials.

That rule means a lot more certified deconstruction experts are needed. Tuesday, the city let us into a hands-on workshop at a home on Northwest 23rd Avenue, where 15 men and women were learning the trade.

Devon Campbell-Willliams is one of those trainees. He worked as a construction flagger before, and wanted to learn deconstruction technique hands on.

"You don't want to go to straight in and straight up to pry up floorboards, if you do that you could crack the wood and it wouldn't be reusable," he said.

Old boards can become table tops in their next life, or rustic walls in new homes, plaster and concrete turned into aggregate, fixtures like a stained glass porch light or door handles can have a new life.

It's a rule meant to preserve Portland's history and keep neighbors safe from harmful dust and chemicals that would come from a wrecking ball. Deconstruction is a process that costs developers $6,000-$8,000 on average if it's done by a certified company. It's meant as a financial disincentive to take down these classics, and it's working.

According to the city of Portland, between 2014 and 2015, 33 percent of all homes demolished in Portland were built before 1916. In 2016 before the rule went into effect, that number jumped to 38 percent. But once deconstruction became mandatory last year, it's down to 24 percent of homes. That's a 14 percent drop.

"This is really just a start for us," said Alisa Kane with the city's Bureau of Planning and Sustainability office. "We think we can go further into homes that are 75 years old or 50 years old but we wanted to start with a sensible bite."

The city says it needs time to assess the need for these old materials before it includes newer homes.

It's also the start of a career for these trainees like Campbell-Williams, "I'm going to tell you the truth, I really want to start my own business and this is a good opportunity to try something new and learn some new skills and do something with my life."

Women only make up 8 percent of the trade industry in Oregon. Nora Sackett used to work for OPB and then started taking classes with Oregon Tradeswomen. She knows housing is expensive and hard to come by, but is excited to save a bit of her city.

"I think it's really important. I think it's great to really disincentivize tearing down these beautiful old classic Portland homes, I don't think it's going to completely stop that of course though," she said.

Sackett, and several other trainees, already have jobs lined up with one of the 12 deconstruction firms in the city. They are in need of a lot of people. If you're interested, contact the city's Bureau of Planning and Sustainability.