John St | Warners Bay
$600K siphonic drainage and roof replacement above a 5,000m² Coles supermarket at John St Warners Bay. Rusted box gutters were dropping water onto shoppers. Compounded by a previous contractor's alteration that had killed the siphonic drainage system. Re-engineered Syphon Drainage system, 25-year warranty. Worked 10pm–6am so Coles never closed.
A 5,000m² shopping centre roof above a Coles supermarket had two compounding problems. The two box gutters had rusted through and were dropping water into the tenancy below every time it rained — directly onto the shopping floor, where elderly customers were slipping and complaints were stacking up. On top of that, a previous contractor had altered the building's siphonic drainage system at some point in its history. The alteration had broken the engineered hydraulic logic, and the system no longer worked. ISPT, the asset owner, needed both problems fixed — without Coles losing a single trading day.
The Challenge
- Major tenant impact. Water from the box gutters was hitting the Coles shopping floor, creating slip hazards for elderly customers and driving complaints away from the centre.
- A previous alteration that broke the engineering. The siphonic drainage system had been modified at some point. Siphonic systems work because the entire pipe network operates as one engineered hydraulic unit — alter one node and the whole system fails. That's what had happened here.
- No room for closure. Coles had to keep trading. ISPT and Turner Townsend (project managers) were not going to approve any program that involved closing the supermarket.
- Live building, live trades. Mechanical, electrical and fire services were all running through the roof space. Works had to be coordinated with the incumbent contractors maintaining each system.
Approach
Three principles drove the methodology: keep Coles trading, re-engineer the siphonic system properly, and coordinate cleanly with the existing service contractors so nothing got broken in the process. This is the institutional-asset rigour our roof repairs and replacement service applies to every shopping centre and live-tenant job.
- Night shifts for any work above the tenancy. All works inside the building — anything that risked impact on Coles operations — ran 10pm to 6am, outside Coles trading hours.
- Day shifts for external roof works. Roof sheet replacement, box gutter installation and external siphonic pipe runs ran during the day to maximise productivity.
- Hydraulic engineer engaged for the siphonic redesign. Syphon Drainage Systems brought in to redesign and certify the system — not patched back to the original spec, but redesigned for the actual roof footprint and rainfall loading.
- Coordinated interface with fire, mechanical and electrical contractors. The incumbent service contractors were briefed on the program; works above their installations sequenced around their access requirements.
Execution
- Roof & Gutter Replacement
- 5,000m² of rainfall catchment area remediated.
- Both box gutters fully replaced — no patching, full removal back to substrate.
- Flashings, cappings and termination details renewed at every junction.
- Siphonic Drainage Re-Engineering
- System redesigned by Syphon Drainage Systems — the previous alteration removed from the network entirely.
- New siphonic outlets, pipework and discharge runs installed to the redesigned hydraulic specification.
- System tested and commissioned under load.
- 25-year manufacturer warranty issued on the Syphon system.
- Building Associated Works
- Internal building works coordinated with the fire, mechanical and electrical contractors maintaining each service.
- All access above Coles tenancy carried out 10pm – 6am to keep the supermarket trading.
- Daily handover and clean-down before Coles opened each morning.
For shopping centre managers and asset owners scoping similar problems, our overview of 5 common causes of roof leaks covers the diagnostic basics before any builder is engaged.
Outcome
- Coles never closed. Four-month program delivered without a single lost trading day. 10pm–6am shifts kept the supermarket operational throughout.
- Tenant complaints stopped. Water ingress eliminated. Slip risk for elderly customers gone.
- Siphonic system back in spec. Re-engineered by the original system specialist, certified, and tested under load.
- 25-year warranty issued. Manufacturer-warranted system documentation provided to ISPT for asset records and future tenant disclosures.
- Clean handover to incumbent service contractors. Fire, mechanical and electrical installations untouched and uncompromised.
Project Significance
John Street is the project we point to when an institutional asset owner asks the question that matters most: can you do major roofing works over a live retail tenancy without disrupting trade? The answer is yes — but only with the right shift pattern, the right hydraulic engineer back on the job, and a builder who treats the tenant's trading hours as a hard constraint, not a preference. If you're an asset manager, project manager, or institutional owner with a shopping centre, large commercial or industrial roof and a major retail tenant who can't close, this is for you.
The harder lesson is the one about siphonic systems. Siphonic drainage is high-performance engineering — it moves more water through smaller pipes by treating the whole network as a sealed hydraulic unit. That's also why it fails catastrophically when someone alters one node without re-engineering the rest. The fix isn't to patch back to the original drawings; it's to redesign for the building as it actually exists today and re-certify the system end to end. That's what we did at John Street, and that's why the warranty stands.
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