The “Glossy Brochure” stage of a new building often hides a messy reality underground. For developers and new owners, stormwater defects are frequently discovered too late—usually during the first major storm after the builder’s warranty has expired.
Stormwater infrastructure is out of sight and often out of mind. Consequently, it is one of the most common areas for construction shortcuts. These defects don’t just cause puddles; they cause basement flooding, structural undermining, and EPA fines.
Based on our audits of hundreds of newly completed sites, here are the 5 most common defects we find and why you must catch them before handover.
1. The “Concrete Tomb” (Construction Debris in OSD)
It is an all-too-common scenario: the On-Site Detention (OSD) tank is built early in the project and then used as a convenient dumping ground during construction.
The Defect: We frequently open inspection hatches to find OSD tanks filled with hardened concrete slurry, brick off-cuts, sediment, and trash. This drastically reduces the tank’s storage volume.
The Cost: Removing hardened concrete from a confined space is incredibly expensive and difficult. If left unchecked, it blocks the discharge outlet, causing the system to fail and flood the property immediately.
2. The “Phantom” Orifice Plate
The Discharge Control Pit (DCP) regulates water leaving the site via a small metal plate with a specifically sized hole (the orifice). It is the critical component for Council certification.
The Defect: The plate is often missing entirely, installed at the wrong height, or the hole is the wrong size. Builders sometimes remove them to drain the site faster during construction and “forget” to reinstall them.
The Cost: Without this plate, the system is non-compliant. Council can refuse the Occupation Certificate (OC), or you may face fines for discharging water too fast into the public network.
3. Incorrect Pump Specification
Pumps are the heart of a basement drainage system. In an effort to cut costs, the “spec” often changes between design and installation.
The Defect: Installing cheaper, undersized pumps that cannot handle the “head” (vertical distance) required to push water to the street. We also see single-pump systems installed where dual-alternating pumps were specified for redundancy.
The Cost: When a single pump fails (and it will), the basement floods. Replacing a submerged pump system and cleaning up a flooded carpark costs thousands—far more than the saving on the cheaper pump.
4. Reverse Grading (Water Flowing the Wrong Way)
Water flows downhill, but sometimes the pavement doesn’t.
The Defect: Surface drains and grate levels are set too high, or the surrounding concrete is graded away from the drain. This creates “birdbaths” (permanent puddles) or directs overland flow into lift shafts and foyers instead of the stormwater pit.
The Cost: Rectification requires ripping up and re-laying concrete driveways or expensive grinding and resurfacing works.
5. Missing Filtration Baskets (GPTs)
Gross Pollutant Traps (GPTs) are required to stop litter and oil entering the waterways.
The Defect: The concrete pit is installed, but the internal “guts”—the mesh baskets, oil baffles, or filter cartridges—are missing. Sometimes they were never ordered; sometimes they were stolen or damaged.
The Cost: If the EPA or Council inspects the site and finds pollutants leaving your property, the fines are substantial. Retrofitting these components post-construction can be logistically difficult if access is restricted.
Summary: Audit Before You Sign
Once you sign off on practical completion or the defect liability period ends, these problems become your problems.
Don’t assume that because it’s a new building, the stormwater works.
Stormwater Services Australia provides independent Pre-Handover Inspections and Defect Liability Audits. We go underground, run the cameras, and check the pumps to ensure you get exactly what you paid for.
Approaching the end of your warranty period?
[Book a Defect Liability Audit] today to catch these costly issues while the builder is still responsible.
