Abstract: A method and apparatus for anchoring an inflatable membrane form to the base wall of a building to be covered by a concrete shell incorporates a groove formation at the top inner face of the building base wall, the groove formation comprising a horizontal shelf of width W1, a recess of height H1 and width W2, and a vertical wall segment of height H2. The edge portion of an inflatable membrane form is wrapped in a multiplicity of elongated wood rail members of height H3 and width W3, with H3<H1 and W1>W3>W2, and the rails are inserted into the groove formation recess. A multiplicity of elongated steel retainer plates of flat, open, C-shaped cross-sectional configuration, mounted on bolts projecting from the shelf portion of the groove formation, aid in holding the wrapped rails and form edge in place when the form is inflated.