patio project

Eco-Patio & Drainage Master Plan

A comprehensive, step-by-step guide to replacing a 12' × 12' cracked concrete patio, solving basement moisture, routing 4 downspouts to a drainage canal, passing through existing fencing, and utilizing St. Louis waste-stream materials.

Part 1: Engineering & Slope Calculations

Water management relies entirely on gravity and precision grading. You have two separate slopes to calculate for this project to function properly:

1. Patio Surface Slope

To keep water out of your basement, the ground must actively shed water away from the house foundation.

  • The Rule: The patio surface must drop 1/4 inch per horizontal foot (a 2% grade).
  • The Calc: For a 12-foot patio, the edge furthest from the house must be exactly 3 inches lower than the edge touching the house.
  • Sub-grade: This slope must be established in the dirt beneath the patio, not just the top level. Water that permeates the Urbanite will hit the compacted dirt base and flow away.

2. Underground Pipe Slope

To move water from 4 downspouts out to the canal without clogging, the pipes need a consistent pitch.

  • The Rule: Gravity-fed drainage pipes require a minimum slope of 1/8 inch to 1/4 inch per foot (1% to 2% grade).
  • The Calc: If the canal is 50 feet away from the patio edge, the trench must drop an additional 6.25 to 12.5 inches from the start of the trench to the canal outfall.

Part 2: Drainage System Design (The Downspouts)

For a system collecting 3 to 4 downspouts, you need smooth flow to handle heavy St. Louis spring downpours without backing up.

Pipe Material

Do not use black corrugated pipe. It crushes easily, and the ridges trap debris and freeze in the winter. Use 4-inch solid PVC pipe (SDR-35 sewer pipe or Schedule 40). If all 4 downspouts combine into a single "trunk" line before hitting the canal, upgrade that main trunk line to 6-inch PVC to handle the massive volume.

Downspout Tie-ins (Catch Basins)

Do not pipe downspouts directly into the underground line. Install a Catch Basin (like an NDS 12" basin) directly under each downspout. The downspout pours into the grate, and the pipe carries it away. This allows leaves to be caught in the basin grate, preventing impossible-to-reach underground clogs.

Cleanouts

Install a Y-fitting with a threaded cap (a "cleanout") at the start of the main line and every 50 feet. If a severe clog ever happens, you can easily snake the line without digging up your meticulously graded yard.

Part 3: The Fence Pass-Through & Bioswale Trenches

To route water from the neighbor's side of the fence into your yard's mulch trenches without undermining the fence posts or flooding the concrete slab, you must utilize a direct pass-through method.

1 Capture on Source Side

Plumb the neighbor's downspouts directly into a 4-inch solid PVC pipe. Run this pipe along the surface (or slightly trenched if there is soil) directly to the base of the wooden privacy fence.

2 The Pass-Through Port

Using a 4.5-inch hole saw, cut a precise circular hole through the bottom fence picket/kickboard, just above the concrete grade.

3 The Transition

Pass the 4-inch PVC pipe through the hole. Attach a PVC Grate or a Pop-up Emitter to the end of the pipe immediately after it passes through the fence to keep critters out.

4 The Mulch Basins (Bioswales)

The 24-inch trenches filled with mulch act as a biological sponge. Terminate your PVC pipe exactly at the head of these trenches so water percolates slowly into the clay without surface erosion.

Part 4: Step-by-Step Execution Phases

Phase 1: Demolition & Harvesting

The "Urbanite"
  • Break the Slab: Using a sledgehammer or rented electric jackhammer, break the existing 12' × 12' slab into manageable, puzzle-piece chunks (roughly 12" to 24" across).
  • Stack and Sort: Move these pieces aside. This is your "Urbanite"—a zero-waste, free paving stone.
  • Excavate: Dig out the dirt beneath the old patio to a depth of about 6-8 inches (to make room for the new base).

Phase 2: Foundation Waterproofing

Protection
  • Inspect: With the old slab gone, inspect the exposed foundation wall for cracks.
  • Seal: Fill cracks with hydraulic cement or polyurethane caulk. Paint the exposed exterior wall with a heavy rubberized foundation waterproof coating (like Thoroseal or Drylok).

Phase 3: Trenching & Pipe Laying

Plumbing
  • Dig Trenches: Dig the trenches for your PVC pipes before building the patio base. Run the pipes alongside the patio footprint, not directly under it if possible (to avoid future settling).
  • Lay the Pipe: Lay the 4" PVC, starting from the catch basins and working toward the canal. Use a 4-foot level with a small block taped to one end to ensure your 1/8" per foot slope is consistent.
  • Bury & Hide: Cover the pipes with dirt. As the pipes pass the garden area, disguise the trench line with mulch, native plantings, or a dry creek bed aesthetic on the surface.

Phase 4: The Permeable Patio Base

Sub-structure
  • Grade the Dirt: Tamp the excavated dirt so it pitches 3 inches away from the house.
  • Weed Barrier: Lay a commercial-grade woven geotextile fabric over the dirt to prevent weeds and stabilize the soil.
  • Gravel Base: Add 4 inches of crushed limestone (CA-6 aggregate). Tamp it down with a rented plate compactor. Make sure this layer also follows the 3-inch drop.
  • Sand Bedding: Spread 1 to 1.5 inches of coarse concrete sand over the compacted gravel. Screed it smooth using a long 2x4 and a level.

Phase 5: Surface Assembly

The Artist's Touch
  • Lay the Urbanite: Place your broken concrete chunks into the sand bed like a giant mosaic puzzle. Leave 1-inch to 2-inch gaps between the pieces.
  • Level: Use a rubber mallet to tap the pieces so they sit flush with each other.
  • Accents: If you have salvaged St. Louis street bricks, use them to create a border perimeter, or break them in half to fill awkwardly shaped gaps between the Urbanite.
  • Joint Fill: Sweep fine gravel, crushed stone dust, or polymeric sand into the joints. Alternatively, sweep in a mix of soil and creeping thyme seeds so green mossy lines grow between the stones, absorbing rainwater.

Part 5: Local Sourcing & Materials (St. Louis)

Because you are utilizing waste-stream materials, your costs will be significantly lower than a standard paver patio.

Material Category Recommended Local Source Purpose
Urbanite Pavers The existing broken concrete slab. Primary patio surface. Saves disposal fees and material costs.
Reclaimed Brick Refab St. Louis or local architectural salvage yards. Accent borders, step treads, or gap fillers.
Crushed Limestone Local quarry (e.g., Fred Weber or Bussen Quarries). Ask for "CA-6" or "Minus" gravel. Creates a solid, non-shifting, permeable base.
PVC Drainage Pipe Menards, Home Depot, or Plumbers Supply Co. 4" Solid SDR-35 or Sch. 40 for routing downspouts to the canal.
Garden Camouflage Missouri Botanical Garden plant sales or Missouri Wildflowers Nursery. Deep-rooted native plants (Switchgrass/Blazing Star) hide trenches and absorb runoff.

Extra Pro-Tips for the Project

  • The "Optician's" Level: When setting your PVC slope, take a 2-foot carpenter's level and tape a 1/4-inch piece of wood to one end. When you place the level on the pipe (with the block on the downhill side), the bubble should read perfectly level. This guarantees you are hitting exactly 1/8" drop per foot without having to do complex math in the muddy trench!
  • Urbanite Aesthetics: Concrete chunks look incredibly beautiful if you stain them. You can use a diluted, eco-friendly iron sulfate wash to give the gray concrete a rich, rusty, earthy brown color before you lay them in the sand.
  • Hole Saw Trick: When you cut the hole through the fence with a hole saw, paint the inside of the freshly cut wood with a little exterior primer or sealant before sliding the PVC pipe through. This seals the raw wood fibers from any stray moisture, preventing rot.