We investigate how overburden weight acts in conjunction with heterogeneity in elastic properties between sedimentary layers to induce the tensile stress necessary for regional jointing. Model results are supported by data from a new experimental design in which an aluminum loading frame sandwiches a tabular specimen of brittle material of varying thickness between two layers of rubber. Load is applied perpendicular to the layering. The aluminum load frame only permits the rubber layers to expand in one direction, leading to the formation of a system of parallel fractures in the brittle layer as the rubber extends uniaxially. The initiation of the first fractures is independent of the layer thickness. As fracture spacing decreases below the layer thickness, mechanical interaction between closely-spaced fractures limits the initiation of additional fractures. The onset of mechanical inhibition of additional fracture growth occurs at greater normalized fracture spacings in thinner layers.