LYNN – It takes a walk down to City Hall’s boiler room and a climb up a shaky metal ladder into a dark, packed-dirt crawl space to learn why the city says it needs to spend $217,000 fixing the building’s front steps.The cavern-like crawl space is hemmed in by concrete walls crisscrossed with iron reinforcing bars stained and corroded by seven decades of dampness and salt sprinkled on the steps during the winters.”The girders and beams underneath the steps are very deteriorated,” said city Inspectional Services Director Michael Donovan.Donovan said Marlborough-based Patriot Restoration employees will work through May chipping away loose concrete pieces and removing rotted reinforcing bar. The work will unfold under the feet of people walking in and out of City Hall – only half of the stairway facing Essex and Market streets will be blocked off during the restoration.The granite steps will not be replaced, but Patriot workers will reseal the joints between the steps before they finish the stairway project. Donovan said a City Hall maintenance inspection pinpointed the rotting concrete and support beams beneath the steps.”A couple of years ago we figured out we had a problem,” he said.City councilors included the City Hall steps on a list of maintenance projects, including parks, playgrounds and the Lynn Common bandstand, approved last February and paid for with bond financing.Donovan said the steps are used not only during the daytime but at night when audiences stream into Veterans Memorial Auditorium for shows.City Facilities Director Lloyd “Butchie” Barnes said city maintenance workers in years past opened the crawl space access door on winter days so that heat from the building’s big boilers filled the space and warmed the steps to the point where ice melted on them.Restoring the steps is a small project compared to equipping the auditorium with air conditioning last year, Donovan said. That project cost slightly less than City Hall’s $1.4 million construction price in 1947 dollars.Donovan said the building needs additional work, including lighting improvements in city offices.