Systems and methods are provided for re-purposing discarded asphalt shingles as soil stabilizers in building and land surface constructions. Discarded (and typically “degraded”) Asphalt Shingles (DAS) are placed beneath building foundation slabs and parking lots in overlapping patterns to replace a measured amount of removed expansive soil to serve as a moisture barrier. DAS can be utilized beneath parking lots in areas of expansive soils by layering the shingles in overlapping patterns to create a moisture barrier from water intrusion from above or below. Building block system (BBS) units may be produced to facilitate handling and transport of the DAS materials to the construction site.