The national cost-per-square-foot is wrong in both directions

Almost every construction-cost assumption in lending starts life as a national average. A cost-per-square-foot figure gets pulled from a survey, applied to a property and carried forward into an appraisal, a draw schedule or a renovation loan. It is a reasonable thing to do when nothing better exists. Something better does exist, and it has been public the whole time. Every state department of transportation publishes bid tabulations: the actual unit prices contractors submitted to win government work. These are not estimates or survey responses. They are contract prices, recorded at the moment a real company committed to doing the work at that number, and most states put them online without a login. We pulled the winning bids on 1,233 public contracts for a single, standardized item — concrete flatwork placement, the sidewalk line item — from the published bid tabulations of 16 agencies, covering 26 metropolitan areas. Each is the winning bid on a 4-inch sidewalk line of at least 300 square feet, let between 2023 and 2026. Prices are shown as bid, not adjusted for inflation. The same item, priced about three times apart At the low end of the range, installed concrete flatwork bids...