Health and Safety Code § 9631
ARTICLE 2. Structural and Material Requirements of Community Mausoleums and Columbariums
Where any wall is constructed against a bank of earth, rock, or other porous material, or where crypts are adjacent to an outside building wall below grade, the wall shall be adequately waterproofed. Before backfilling, a waterproofed wall shall have a protection board placed against it to prevent damage to the waterproofing during backfilling.