Like our 20" riser, we have combined all the best features of concrete and plastic risers to create our patented riser system. Our risers hold their shape, are stackable, screw together, and are water and airtight. Structural ribs inside prevent frost from adhering to the riser in frost prone areas.
U.S. Patent No# 6,655,093; 6,688,072; 6,484,451; 6,877,281