The continuous growth of black hole interior volume is a robust semi-classical phenomenon. Christodoulou and Rovelli showed that the max-imal interior volume of a Schwarzschild black hole grows linearly withadvanced time with a universal coefficient. Related developments in holog-raphy suggest that this growth is tied to irreversible information-theoreticdynamics, often discussed in terms of quantum complexity, indicating thatblack hole interiors are intrinsically dynamical.In this work we develop a covariant, horizon-scale effective frameworkin which interior growth is interpreted as the production of spacetimevolume mediated by localized horizon dynamics. Spacetime is modeledas a granular medium characterized by elementary quanta of geometryand a maximal admissible density. Horizons are treated as active inter-faces where infalling energy contributes to the creation of interior volumethrough a local phenomenological conversion law. The framework is for-mulated covariantly by supplementing the Einstein equations with an ef-fective geometric sector and a covariant exchange current, ensuring localenergy–momentum conservation, causal consistency, and the absence ofpreferred frames.A central quantitative result is that, once the horizon conversion coef-ficient is fixed by a single semiclassical matching condition, the frameworkreproduces the Christodoulou–Rovelli interior volume growth coefficientfor Schwarzschild black holes, without introducing additional free param-eters. This fixes the normalization of the effective conversion law in thestandard effective-field-theory sense.After this calibration, the framework yields parameter-free semiclas-sical consequences at horizon scales, including universal mass scaling ofthe growth rate, extensions to rotating and charged black holes, and con-trolled estimates of suppressed corrections to redshift drift and quasi-normal modes, organized in powers of ℓ2eff /R2s .1We emphasize that the construction is phenomenological: no micro-scopic derivation from loop quantum gravity, string theory, or holographyis assumed. Rather, the framework provides a covariant and testable effec-tive description of interior volume production consistent with establishedsemiclassical benchmarks.