Services & Drainage
Blocked & Undersized Stormwater
Blocked and undersized stormwater infrastructure is one of the most common causes of building flooding and water damage in Class 2 buildings. Stormwater systems sized to the minimum requirements at the time of construction may be inadequate as development increases impervious areas or as climate change increases rainfall intensity. Blocked pipes from debris, tree root intrusion or collapsed sections prevent even correctly-sized systems from functioning, rapidly leading to surcharge, overflow and ingress.
Common Signs
- Surface flooding on car park levels and podium areas during rain
- Overflowing pits and surcharging grate inlets during moderate rain
- Water entering the basement from overwhelmed surface drainage
- Gurgling noises in drainage pipes indicating partial blockage
- Slow drainage from roof outlets and balcony drains
- Tree root intrusion visible at inspection pit openings
- Surface staining below corroded or leaking stormwater pipes
Common Causes
- Debris and sediment accumulation blocking pits, pipes and outlets
- Tree root intrusion into older clay or concrete stormwater pipes
- Collapsed or deformed pipe sections restricting flow
- Pipe sizes designed below current AS/NZS 3500.3 requirements
- Increased upstream catchment area from subsequent development
- Inadequate maintenance cleaning frequency
- Pit lids and grates replaced with solid covers blocking inlet capacity
Risk of Neglect
- Flooding of basement car parks and lower building levels during storm events
- Water ingress to the building structure from overwhelmed drainage
- Damage to vehicles, building services and stored property in basement
- Insurance claims and strata liability for flood damage
- Safety hazard from rapidly rising water in basement areas
- Tree root damage to stormwater pipes extending to adjacent structures
- Long-term structural damage from repeated saturation of substructure
Inspection Requirements
Download Inspection Checklist- CCTV inspect all accessible stormwater pipes to identify blockages, root intrusion, deformation and joint failure.
- Inspect all pits for debris accumulation, condition of benching, and inlet grate capacity.
- Assess the diameter of all stormwater pipes against the contributing catchment area.
- Conduct a hydraulic capacity check of the drainage system against AS/NZS 3500.3 design storm requirements.
- Inspect all roof outlets and balcony drains for blockage and correct grate opening area.
- Check all stormwater discharge points to the council system or absorption trench.
- Engage a hydraulic engineer where system capacity is in question or flooding is recurrent.
- Review council drainage records for the downstream system capacity.
Start Inspection Checklist
Create a project inspection record, add defect locations, upload photos, and save notes for scope writing.
Typical Repair Methodology
- 01.Conduct a high-pressure water jetting clean of all stormwater pipes to remove debris, sediment and root intrusions.
- 02.CCTV inspect pipes post-jetting to assess structural condition and identify any remaining defects.
- 03.Reline or replace pipe sections that are collapsed, deformed or structurally compromised.
- 04.Clean all pits and sumps of sediment and debris accumulation.
- 05.Replace all blocked or damaged inlet grates with grates of the correct open area.
- 06.Upsize pipe sections identified as hydraulically undersized through the hydraulic assessment.
- 07.Install additional pits and inlets where the catchment area or inlet spacing is inadequate.
- 08.Root treat identified root intrusion zones with foaming root killer and re-CCTV after 30 days.
- 09.Establish a maintenance programme for annual jetting and inspection of the stormwater system.
- 10.Record all works with CCTV reports, pipe schedules and photographs.
Related Repair Systems
- High-pressure water jetting systems
- CCTV pipe inspection services
- Stormwater pipe relining systems
- Pipe replacement and upsizing programmes
- Pit and grate upgrade systems
Open Repair Systems →