The long-feared (by some) invasion of duplexes into Arlington’s single-family enclaves is shaping up as a minor incursion.

The county’s 20-month-old Missing Middle housing initiative, aimed at countering our explosion of luxury home-building to expand opportunities for aspiring middle-class owners, turned a corner last month.

An April 28 draft framework “Missing Middle Housing Study: Expanding Housing Choice” (plus the staff’s follow-up public session via Zoom May 3) set a modest scope for the envisioned loosening of decades-old zoning restrictions.

Yet the critics — defenders of the single-family lifestyle and our threatened trees — are not reassured.

Using models from crowded jurisdictions such as Minneapolis and Portland, Ore., the latest proposal from Housing Arlington is ambitious only in that it would permit multi-family structures nearly countywide. The exceptions are the neighborhoods already containing duplexes, triplexes and quadraplexes, plus residential sections within the separate Plan Langston Boulevard initiative.

As laid out with detailed data by Matthew Ladd, Kellie Brown and Richard Tucker, the new zoning freedoms for landowners and builders would allow more reasonably priced structures by encouraging smaller units grouped more densely. Think of families with incomes from $108,000-$200,000. One could expect a “gradual pace of growth” that might total 20 lots, 94-108 units, or 150 “new neighbors” per year, “geographically dispersed.”

Such additions “can be accommodated with existing infrastructure,” and the net increase in school enrollment likely only 9-13 students per year. “Stormwater runoff would be comparable to current impacts from single-detached redevelopment,” the study asserts, and a “tree canopy of 20 percent to 50 percent is achievable.”

The analysts’ confession acknowledges that “most redevelopment in residential areas would continue to be single-detached” homes. Missing Middle style “has inherent economic disadvantages”— increased costs to build, complexity for ownership and sales, and lack of market familiarity.

But the county should nonetheless proceed, they recommend, in part because of the board’s equity theme—to offset past racial exclusion.

With 70 percent of Arlington zoned single-family, how might those residents benefit? Besides contributing to equity, answered Kellie Brown, they might consider the need to “preserve workforce loyalty” in Arlington and the fact that “their future needs may change”—they might have an aging parent or child who needs less expensive digs.

Peter Rousselot, the longtime skeptic at Arlingtonians for Our Sustainable Future, told me: “The county has not addressed previous concerns about ameliorating the severe fiscal, environmental, and income-inequality metrics of adding roughly 65,000 new residents as projected in 2018.” The new approach would “exacerbate the problem and doesn’t provide new options for anyone earning under $115,000. The market, not the county, will decide the pace of redevelopment.”

The Arlington Tree Action Group faulted the study for vagueness and for not mentioning climate change. “The canopy is declining while impervious surface is expanding,” it said, “unsustainable” trends that Missing Middle zoning could “accelerate.” ATAG backs a 20 percent tree canopy minimum. “Reducing it to a multi-family standard of 15 percent or a site plan standard of 10 percent reduces the tree replacement rate and will fast-track tree loss.”

Still being negotiated, staff say, are tricky “nitty gritty” issues of parking-space requirements, design standards and what incentives might prompt builders to pursue Missing Middle.

The public can provide input through May 27, with proposed zoning code amendments for the county board planned for this summer and fall.

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Arlington references abound in famed Watergate reporter Carl Bernstein’s new book “Chasing History,” describing his adventures as cub at the Evening Star.

In 1960-63, Bernstein and four other aspiring scribes were roommates at 6049 N. 18th St. near Westover. He describes backyard barbecuing, rap sessions and his homemade desk in what seemed like “a mansion”— six bedrooms and a butler’s pantry in the “white-painted brick mock Colonial in an ordinary suburban neighborhood” surrounded by civil servants, merchants and teachers.

I contacted the owners, who were unaware of Bernstein’s book. But they called back to confirm that her family, who built the home, had rented it out during those heady days.