We argue that a design commons can be an advantageous organizational form under two salient conditions: 1) high "subtractability" because different claimants have mutually exclusive beliefs or preferences with respect to the design form, and 2) low "excludability" in the sense that the designed artifact must be shared. Our paper is based on an empirical study of a commons organization created to design new school buildings. We argue that the design commons organization induced teachers to volunteer their knowledge and preferences, which otherwise would have been difficult to elicit. Although governance was a struggle, none of the cases in our sample suffered a "tragedy of the commons" in terms of budget overruns, bogged-down processes or free riding. Using the principles of Ostrom's commons theory, we show that the design commons organization was robust, although it displayed some areas of fragility. We conclude with the rudiments of a contingency theory describing when and why a commons organization can be advantageous for design production. We also discuss design flexibility as an intervening variable that is critical in intermediating conflicts that commons organizations cannot resolve.