But something is missing. Surprisingly, the effort fails to promote the creation of additional units within existing buildings. With new units in multiple-family housing often costing more than $400,000 each, we should be looking not at new housing to solve the supply and affordability crisis but at existing buildings.

Think about it. Boston has thousands of dwellings that already have roofs, walls, foundations, and utilities in place. All we need is to settle on economical, sustainable, and elegant ways of adding apartments to these buildings. Most of our housing units were produced for households far larger than those currently occupying them. The average occupancy in a Boston dwelling is 2.49 residents. With increases in single, elderly, and millennial households, Mayor Martin Walsh anticipates fewer than two residents per new unit. Why build from scratch when we can simply create new units within existing walls?

Although we don’t pay nearly enough attention to the precedents, they are all around us. J. E. Barlow & Company’s Brighton row house development, at Commonwealth Avenue and Wallingford Road, is one. In 1909, Barlow built 50 two-story brick row houses. Each had a kitchen, dining room, parlor, and hall on the first floor, with four bedrooms and a bathroom above. In 1917, one owner installed a bathroom on the first floor, converting his house into two apartments. Others soon followed suit: Several conversions came in the 1920s; the most recent was in 2012. Some carved three units out of the houses; two doctors and a dentist created live-work spaces with residences above ground-story offices. Today, only 22 houses have not been converted; there are 86 units in the place of the original 50.

In 1892, architect Arthur G. Everett designed himself a rambling 2½-story Victorian house on Chestnut Hill Avenue. He lived there with five members of his family and two servants. By the 1970s, Everett’s house had four units; later, two additional units were added — six perfectly serviceable units in the place of one. The density of additional residents gives vibrancy and vitality
to the neighborhood.

Boston has 15,000 triple-deckers. They have many common elements. Imagine streamlining a permitting and contractor trades program called Three + One, developing design templates for easily adding one more apartment to these buildings (adjusting zoning and building ordinances as necessary). Investing in existing dwellings stabilizes them while making them more useful. We would get to 53,000 “new” units less expensively, more quickly, and much more sustainably. Adopting this vision, we could easily zoom right past that ambitious goal.

Kyle Nelson is an illustrator and art director at Stoltze Design.