Choosing between scores of new apartments and the sliver of inconstant San Francisco sunlight they might eclipse, the Board of Supervisors voted for the sun — and proved the biblical aphorism that there is nothing new under it. In a city desperately short of dwellings, development proposals come and (mostly) go, but the supervisors’ housing obstructionism is eternal.

In case there was a shadow of doubt that the ideology at work here is less pro-sun than anti-housing, the board this week also passed Supervisor Gordon Mar’s resolution against SB50, a bill to allow higher-density housing near transit. In the space of a single meeting, the supervisors thereby blocked housing in both theory and practice.

The proposed South of Market building, assuming a fog-free midsummer’s night, would cast a shadow over up to 18.24 percent of Victoria Manalo Draves Park for as long as 110 minutes. That’s the maximum: The building would throw little to no shade on the park for much of the year, according to an exhaustive analysis, and would reduce annual sun exposure by a grand total of 0.38 percent.

On the bright side, the building, which had been approved by the Planning and Recreation and Park commissions, would provide 63 apartments, nearly a third of them designated affordable. The would-be developer, Paul Iantorno, has pledged to replace the four rent-controlled units it would displace and house their tenants during construction. He even agreed to pay three years’ worth of wages for an attendant to shoo drug users out of the bathrooms at the supervisors’ beloved park. As Mayor London Breed noted, “You cannot claim to be pro-housing and then reject projects like this one.”

Somehow none of this made it a close call for the supervisors, who voted 10-0 against the development. The decision made a powerful if inadvertent case for legislation like SB50, by state Sen. Scott Wiener, which they formally opposed by passing Mar’s measure 9-2.

Granted, the more rigorously enforced fossilization of the city’s wealthier neighborhoods hurts the case for building in places like SoMa — just as San Francisco’s housing denial enables more flagrantly exclusive policies in the suburbs. Local officials throughout the region will find shady reasons to reject housing until they’re relieved of their veto authority.

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