St. Louis Commercial Rainwater
Retrofit & Remediation
Engineering a surface-mounted header system to intercept a 1,215 sq. ft. roof footprint, bypassing solid concrete barriers to cure decades of basement flooding on the left elevation.
Project Scope & Goal
We are engineering a structural solution to capture the runoff from your 1,215 sq. ft. multi-family footprint. Specifically, we are targeting the 31.4' wall on the left side of the property where high-volume downspouts are trapped between a neighbor's fence and a solid concrete side-yard.
Traditional excavation is impossible here. Our goal is to surface-mount a heavy-duty commercial PVC header along the brick, slope it outward, and route it to a 2,500-gallon cistern. We will leverage the MSD Project Clear Small Grants Program (up to $10,000 for multi-family/commercial) to fund the entire system.
- Cure multi-decade basement flooding.
- Leverage J-Industrial zoning for a massive tank setup.
- Exploit the regional waste stream for structural materials.
The Roof Math (St. Louis "J-Zone")
Due to industrial fallout, we must divert the first 60 gallons of rain before filling the cistern.
The Waste Stream Audit
Do not waste grant money on structural base materials. We will source these components from St. Louis's commercial demo and salvage networks.
Commercial PVC & Uni-Strut
Digging concrete is out. We need to surface-mount the header. Source 4" to 6" Schedule 40 PVC and galvanized Uni-Strut channels from local mechanical contractor scrap yards or demolition sites.
Ag / Brewery Tanks
St. Louis's brewing sector is massive. Hunt commercial auctions or Facebook Marketplace for used food-grade IBC totes, stainless conical tanks, or high-density agricultural poly tanks.
EPDM Roofing Scrap
When flat-roof industrial buildings are re-roofed, thick EPDM rubber is discarded. Salvage this to line your gravel tank pad. It prevents weeds and stabilizes the 20,000lb water load.
The 4-Tier Cost Matrix
MSD operates on a reimbursement basis. You must float the capital upfront. Here is the out-of-pocket projection before the $10K check arrives.
Reclaimed DIY
- 4-6 Salvaged IBC Totes
- Surface-mounted salvaged PVC
- Gravity feed (no pump)
(Leaves $8.8k on table)
Standard DIY
- New 1,000-gal farm tank
- Box-store 4" PVC header
- Standard utility pump
(Fully Reimbursed)
Premium DIY
- 2,500-gal Dark HDPE Tank
- 6" Commercial PVC header
- High-flow electric booster pump
- Engineered retaining block pad
(Fully Reimbursed)
Pro / Hired Out
- Hired excavation & grading
- Subterranean fiberglass tank
- Turnkey plumbing & electrical
(Out of Pocket)
Step-by-Step DIY Execution Plan
Chronological order is mandatory. Diverting from this sequence will either void your MSD grant or result in catastrophic structural failure.
Verify your building on the MSD Project Clear map and complete the orientation survey. Submit your site plan emphasizing your multi-family status to access the $10,000 tier. You must wait for a Notice to Proceed before purchasing materials. Early work is not reimbursed.
The left side is trapped by the fence, and digging is impossible due to the concrete. Use a hammer drill to mount Uni-Strut brackets horizontally along the brick on the 31.4' wall. Pitch the brackets with a minimum 1/4-inch per foot slope toward the open yard. Fasten the 6-inch PVC to these brackets.
Cut the existing downspouts along the left wall. Plumb them directly into your new sloped, surface-mounted PVC header pipe using sanitary tees. Crucial: Cap the old cast-iron standpipes in the ground with heavy-duty rubber Fernco caps to prevent sewer gas venting.
At the destination yard (safely away from the foundation), excavate 8-10 inches of soil. Lay your salvaged EPDM rubber. Build a perimeter wall and fill the footprint with 3/4-inch minus gravel in 3-inch lifts, running a rented plate compactor over each lift until perfectly level.
Route the surface header into a high-capacity First-Flush Diverter (sized for ~60 gallons), then into the top of the cistern. Plumb a 4-inch overflow pipe near the top of the tank, routing it at least 10 feet away toward an alley or street drain. Submit all itemized receipts, photos, and the Completion Form to MSD for your $10k reimbursement.
Missouri / St. Louis Structural Warnings
Masonry Anchor Limits
A 31.4-foot run of 6-inch PVC full of water is extremely heavy. You cannot use standard plastic drywall anchors in old city brick. You must use heavy-duty wedge anchors or Tapcons driven directly into the center of the brick face (never the crumbling 100-year-old mortar joints) to support the Uni-Strut brackets.
The Combined Sewer Cap
St. Louis relies on combined sewers. When you disconnect downspouts on the left wall to route them to the new header, you leave open cast-iron standpipes. You must seal these pipes with heavy-duty rubber Fernco caps so raw sewer gas doesn't vent between the houses.
The Freeze-Thaw Time Bomb
St. Louis winters will destroy an above-ground tank. You must completely drain the cistern, the pump, and the first-flush diverter by mid-November. Reconnect a winter bypass so snowmelt routes away from the building, not into a frozen, cracked tank.
The 10-Foot Foundation Rule
Placing an 20,850 lb water tank directly against an old St. Louis brick or rubble foundation is catastrophic. Keep the tank pad well away from the building envelope and ensure the massive 4-inch overflow pipe points firmly downhill away from the structure.