Although communal resources, i.e. public goods, are often critical to society, they are simultaneously susceptible to exploitation, and are evolutionarily stable only if mechanisms exist to curtail exploitation. Mechanisms such as punishment and kin selection have been offered as general explanations for how public goods can be maintained. Evidence for these mechanisms comes mostly from humans and social insects, leaving their generality in question. To assess how public goods are maintained in a novel taxon we observed cooperative nest construction in sociable weavers (Philetairus socius). We observed cooperative nest construction and also collected blood samples, performed next-generation sequencing, and isolated 2,358 variable SNPs to estimate relatedness. We find that relatedness predicts both the amount of time devoted to cooperative nest construction and the number of items inserted into the nest superstructure, while no other morphological characters significantly explain cooperative output. We argue that indirect benefits are a critical fitness component for maintaining the cooperative behavior that maintains the communal nest.