Choosing the Right Gravel for Your French Drain Project

Gravel size is part of an assembly, not a stand-alone answer.

The aggregate provides space for water to move around a collection pipe or within a drainage zone. Its size and grading should be selected with the surrounding soil, filtration, pipe and collection objective. A foundation detail, a yard trench and a manufactured bundle can have different requirements.

DOE footing-drain guidance describes washed stone and filter fabric around the pipe in a specific foundation assembly. That is useful context, not a reason to prescribe the same stone specification for every landscape project.

Cleanliness and fines matter.

Ask whether the proposed drainage aggregate is washed and what grading is specified. Sand, dust and soil fines can occupy the spaces intended to carry water. Decorative stone selected for its appearance may not meet the design's drainage requirements.

Do not assume that a bag labelled gravel is suitable solely because its pieces look large. Confirm the product, grading and application with the designer, installer or supplier.

Filter compatibility is a separate decision.

A geotextile should pass water while limiting soil migration without unacceptable clogging. FHWA discusses those principles in its geotechnical drainage context. Residential selection still needs to match the soil and assembly.

The fabric, aggregate and pipe should be considered together. A pipe sock and a trench wrap are not automatically interchangeable, and the absence of visible fabric does not prove that a manufactured assembly is installed incorrectly.

Quantity depends on the actual drainage zone.

• Get the planned route length and the specified excavation and aggregate dimensions.
• Distinguish gross trench volume from the net aggregate volume around pipe or manufactured components.
• Ask the supplier how bulk volume and weight relate for the selected material.
• Include the agreed installation allowance rather than inventing a universal waste percentage.

Questions for a written estimate.

Which aggregate is specified? Is it washed? What filter material is proposed and why? How will soil be kept out during installation? What restoration follows the excavation?

A clear material description makes estimates easier to compare. It also gives a future repair professional useful information about the installed assembly.