Generally, a layer base material of 50mm (2") Crusher Run or Granular "B" is laid and compacted, followed by a layer of properly compacted 22mm (7/8") Crusher Run or Granular "A".  Most roads are built to the specifications laid out by Engineers, but generally, one needs a minimum depth of 300mm of the sub-base material, followed by depth of 150mm of base material. 

For more information on Road Construction please visit Norjohn Contracting