Drainage for Interlocking Patio Stones

Pavers and Drainage

• The installation method for interlocking stones results in a permeable surface. The gaps between the pavers let water infiltrate and eventually disperse through the soil. This is an effective way of releasing and filtering storm water. In areas near sensitive environments or water bodies interlocking pavers are recommended instead of impervious materials. Segmental pavers are less vulnerable to freeze-thaw cycles than concrete and they're easy to replace and repair. Site preparation and material selection is key for a stable and durable interlocking patio stone installation.

Subgrade and Slope

• Exterior paved surfaces should have a 2-percent slope -- a 2-foot rise for every 100 feet of run -- as a minimum, away from the structure. The subgrade is sloped and compacted to prevent settlement. The material for the subgrade should be a well-draining aggregate mix. A leveling course of sand is laid under the stone, but the sand should be grit sand; builder's sand is very fine and can become waterlogged, causing problems with the subgrade.

Subsurface Drainage

• If the slope minimum can't be met or the water table is high, subsurface drainage may be necessary. Perforated pipe under the surface will collect runoff and discharge it to an approved outlet. An existing storm drain or an open space where the water can infiltrate into the ground is best. Check the specifications for pipe sizing and installation. As a rule, perforated pipe can be used to depths of 4 feet.

Paving Joints

• Interlocking pavers are held in place by sand swept between them; the sand is crucial to establishing the interlock between the pavers. Sand particles for jointing should be sharp to interlock together and the sand needs to be dry. The joints should be completely filled; occasionally it's necessary to replenish the sand. While the patio is permeable, it's important that the installation permit excess water to flow off the surface and infiltrate slowly to prevent washouts and water collection below the pavers.