Over the past several years, it seems that the most common sight on the Boston skyline has become the construction crane: More than $7 billion in construction is reportedly pouring into several of the city’s core neighborhoods, including the Seaport, Back Bay and Fenway. Yet despite all the new developments, Boston’s residents are in an unprecedented housing pinch: Rents are rising at five times the rates of incomes, and households making $80,000 a year can access only the bottom quarter of the housing market, shutting them out of entire neighborhoods.

Rising rents and property values have been a mixed blessing for the city. A strong metropolitan economy and high property values swell the city’s coffers, but those same factors hurt the least among us.

Boston is in the grip of an unprecedented demographic sea change. Though its current population of 655,000 is well below its peak population of 801,000 during the 1950s, the lifestyles and needs of its residents have changed. Boston’s new residents are, by and large, millennials living in a now-outmoded housing stock. The city’s iconic triple deckers, from Back Bay to Hyde Park, which were once designed to suit entire families or function as densely packed rooming houses, are now split by groups of students or young professionals. I’m one of them. I live on the top floor of a triple-decker in Jamaica Plain with two friends. Together, we spread the rent burden across three salaries. That means that less-flexible, working-class families must live farther and farther out from the city neighborhoods that were once built to cater explicitly to their needs.

In response, the city of Boston plans to build 53,000 new units to meet an anticipated demand of 44,000 new units as part of the city’s 2030 plan. Housing is not a problem that can be solved quickly -- population changes take place over decades, and the construction of new units requires a concerted amount of time and energy. Yet what the city plan seems to commits us to is 14 more years of housing purgatory and spiking rents that are currently the third highest in the country, behind San Francisco and New York.

The problem goes beyond the limited budgets of the city's growing class of young professionals or the stark reality of exclusion for first-time homeowners. A city is only as vibrant as its population is diverse.

To wait 14 years to alleviate the housing crisis is to risk losing the broad, intermingled communities that still cling to existence in neighborhoods like the wonderful mishmash of Union Square, now under threat from high property values and rent hikes due to the planned Green Line Extension. To wait is also to risk a city inhabited by only the very rich and the very poor, with no room for economic mobility. (Homelessness in Boston has increased 15 percent since 2011 -- a catastrophe brought to the fore by last year’s closure of the Long Island shelter.