Salt Lake City's 5,000 sq ft minimum lot size made its own missing-middle zoning zones unbuildable — only 4% of eligible lots were developed

Salt Lake City created RMF-35 and RMF-45 zoning districts specifically designed to encourage 'missing middle' housing — duplexes, triplexes, fourplexes, and small apartment buildings. The city went through the political effort of passing the rezoning, branding the initiative, and signaling to developers that these areas were open for business. Then almost nothing got built. The reason: the zones retained a 5,000 square foot minimum lot size requirement, and nearly half of the lots within these zones are smaller than 5,000 square feet. Since the zones were created, only around 4% of lots zoned RMF-35 or RMF-45 have been developed. This is not a hypothetical policy failure — it is a measurable, quantifiable disaster. The city invested political capital, staff time, and public goodwill in a zoning reform that was structurally incapable of producing results because nobody checked whether the dimensional standards matched the actual lot inventory. Developers who looked at these zones quickly discovered that the lots they could afford were too small to build on legally, and the lots that met the minimum size were too expensive to make missing-middle pencil versus single-family. Meanwhile, residents in these neighborhoods continued to see no new housing options between a $500,000 single-family home and a $1,500/month one-bedroom in a large apartment complex miles away. This problem persists because zoning reformers and dimensional-standards writers often operate in silos. The political appointees and council members who vote on rezoning rarely examine the technical dimensional requirements in detail — they focus on the headline ('we're allowing fourplexes!') without stress-testing whether the lot width, lot area, setback, and FAR requirements actually permit a fourplex to be built on a typical lot in the zone. Salt Lake City eventually recognized the error and began amending the zones in 2025-2026, but this pattern — aspirational rezoning undermined by incompatible dimensional standards — repeats in cities across the country. A survey from the National Bureau of Economic Research found that 94% of US communities have minimum lot size provisions, and the average minimum is growing, not shrinking.