Backyard holds water for two days after a storm.

Layout & Slope

• Minimum 1% slope (1/8" per foot) = 7.5" drop over 60'. Verify with a laser level or string line before digging. Swale inlet must be lower than trench end.

Trench

• Width: 12–18". Depth: 18–24" (deeper if you need cover for lawn).
• Line bottom and sides with non-woven geotextile (4–6 oz/sy). Leave 24" excess on each side to wrap over top. Do not use woven landscape fabric—it clogs.

Pipe

• 4" solid PVC SDR 35 or dual-wall HDPE (N-12) with glued/coupled joints. Perforated pipe (ASTM D2729 or F405) only in the wet zone; solid pipe for the last 10–15' to the swale to prevent root intrusion and daylighting issues.
• Perforations down (5 & 7 o'clock). Cleanouts at every bend >45° and every 100' (IPC §1103.1).

Stone

• Clean, washed ¾"–1½" angular stone (AASHTO #57 or #5). No fines, no pea gravel, no "crusher run." Fill to 2" above pipe, then fold fabric over, then 6–12" native backfill.

Clog-Proofing Details

• No sock on pipe—it becomes a filter cake. Stone + fabric is the filter.
• Surface inlet: Use a 12" catch basin with a grate and sump (12" deep below outlet) to trap sediment. Clean it annually.
• Rodent guard: ¼" hardware cloth on swale outlet.
• Maintenance: Jet or snake every 2–3 years.

Code/Regs

• IPC §1103 (drainage piping), IRC §R405.1 (foundation drains—similar principles). Check local grading/drainage ordinance—many require a permit for discharge to a swale or ROW.

If high groundwater or clay pan: Add a second parallel trench 10' away, or go to a dry well/pump. If the swale is flat or backs up, this won't work—get a site grading plan from a civil engineer.

To build a durable, clog-resistant French drain for your 60-foot run to the property-line swale, follow these proven, code-aligned steps (based on IRC R405.1 and ASCE 7-22 drainage principles):

1. Trench Design (Critical for Longevity)

• Width: 12–18 inches (minimum 12” for pipe + gravel)
• Depth: 18–24 inches (minimum 12” below frost line in your zone; confirm local frost depth)
• Slope: Minimum 1% grade (6 inches of fall over 60 ft) — non-negotiable. Use a laser level or string line to verify. Less slope = standing water = clogging.
• Bottom: Line with geotextile fabric (non-woven, 4–6 oz/sq yd, e.g., Mirafi 140N) — extends 6–12 inches up each side to prevent soil migration into gravel.

2. Pipe & Gravel (Clog Prevention)

• Pipe: Use 4-inch perforated PVC SDR 35 (not corrugated flex pipe — it sags and traps debris). Perforations must face down (6 o’clock position) to allow water entry while keeping silt out.
• Gravel: ¾-inch clean crushed stone (no fines — avoid pea gravel or “drainage gravel” with sand/silt). Fill trench to 2 inches below grade.
• Wrap: Enclose pipe and gravel completely in the same geotextile fabric — overlap seams by 12 inches, shingle-style (upper layer over lower) to shed water and soil.

3. Termination & Maintenance

• Outlet: At the swale, end pipe with a rodent guard (hardware cloth or PVC cap with slots) and discharge into a rock pad (2’x2’x6” deep) to diffuse flow and prevent erosion. Never discharge directly into neighbor’s property without easement.
• Inlet: At the high end, use a catch basin with a grate to trap leaves/debris before they enter the drain. Clean grate quarterly.
• Avoid: Trees/shrubs within 5 ft of drain — roots invade pipes. If unavoidable, use root-barrier fabric (e.g., Typar) wrapped around pipe.

Why this works: Proper slope + clean gravel + geotextile separation prevents soil fines from clogging voids. PVC SDR 35 resists crushing and lasts 50+ years. Perforations down + fabric wrap = water enters, silt stays out. Permit check: Verify local stormwater rules — some jurisdictions require permits for drains discharging to property lines or swales. If unsure, consult a civil engineer or licensed landscape contractor (especially if near utilities or septic). Do not use landscape fabric alone — it clogs. Geotextile is engineered for subsurface drainage. Total cost estimate: $8–12/ft DIY ($480–$7