What Is the Purpose of the Gravel Under a Paver Sidewalk?

Support and Drainage

• Gravel as a base under a paver sidewalk serves two purposes. It provides firmer support for the weight put on the pavers and it creates drainage to keep water from building up under the pavers. The depth of the gravel base will vary with the type of soil underneath, the style of paver being used and the expected weight loads on the walk. Heavier pavers need a firmer base. Heavy traffic walks need more support than garden paths.

Weather Affects the Base

• In areas with extreme winters, gravel bases may need to be deep enough to prevent any trapped water from freezing, causing the pavers above to bump up or become unlevel. Some cold weather areas, for instance, recommend gravel bases of 8 to 12 inches, while in milder climates 4 to 6 inches of gravel may suffice. Tight soils like clay which are slow to drain and dry also need deeper gravel bases.

Gravel Is Harder Than Dirt

• Gravel serves as support because rock is harder and firmer than any earth, even heavy clay. A square foot of gravel will support more weight than a square foot of dirt, because the rock is harder and its interlocking rough edges spread the force of the load more. Gravel also is less subject to slipping or movement when wet because of its rough edges, so pavers stay in place better.

Gravel Drains Better

• Drainage is the primary function for a gravel base. Rain and other water can pool or puddle until it is absorbed into soil. The tiny crevices between pieces of gravel allow moisture to drain more quickly away from the paved area or be retained in the gravel until it is absorbed by the soil. Limestone, used for most base gravel, also is porous and can actually absorb and hold some water.