An improved anchoring system for fastening an elastomeric membrane to a roof comprises an anchoring plate with a top planar surface, spaced apart, raised sidewalls over which the membrane may be laid and at least one aperture for securing to a roof. Each sidewall has a retaining lip that extends inwardly from the top planar surface for retaining a spacing insert, a top surface of which has raised flanges, each flange having a retaining lip with a plurality of longitudinally extending gripper ridges. Preferably, the retaining lips on the spacing insert extend over the top surface of the anchoring plate and taper toward one another at one or more areas between their end points. The system further includes a wedge for inserting into a cavity defined by the spacing insert.