Gravel under a French drain creates a stable, permeable base that supports the perforated pipe while allowing water to flow freely without soil interference.
Standard installation guidelines in Houston recommend 2-3 inches of 3/4-inch washed angular stone beneath the pipe to prevent sinking, filter fines, and maintain hydraulic efficiency for decades.
In clay-heavy soils, gravel separation is essential to avoid clogging; however, pre-wrapped pipes or polystyrene aggregates can sometimes substitute in sandy conditions.
Professional engineers specify gravel bedding for footer drains near foundations, as it elevates the pipe for proper slope and handles peak flows.
Skipping gravel risks pipe collapse, silt buildup, and system failure, though budget DIYers occasionally omit it in coarse native soils with geotextile liners.
