“Can subdividing the American dream fix the problem of unaffordability?” That question is posed in a New Republic review of the latest book by urban planning professor Vinit Mukhija, which focuses on the informal, un-permitted units that have proliferated on single-family home lots, providing needed shelter amid an intractable affordable housing crisis. Los Angeles alone has about 50,000 of these un-permitted second units, Mukhija estimates in “Remaking the American Dream: The Informal and Formal Transformation of Single-Family Housing Cities.” Unless more housing is built, we will see more un-permitted units, some of them unsafe, the book argues. It also emphasizes that we must invest in and upgrade existing informal housing units, which play a vital role in expanding affordable options for shelter. As the review notes, “A quiet housing revolution is taking place. But if policymakers don’t adapt to the new construction, the changing market is likely to reproduce the same instability and abuse that poor tenants currently suffer.”