Since 2008 expert witnesses bound by the Rules of District Court (Cap. 336H)

Rooftop Construction Blocked Common Drain – Sewage Backflow Flooded a Home

Construction debris blocked the common drainage pipe during rooftop works, causing sewage to backflow into a residential unit through floor drains. The owner returned home to find the kitchen and bathroom flooded, initially suspecting an internal pipe burst. SILVER SURVEYORS investigated using infrared scanning, water sampling and pipe inspection, confirming the source was a blocked common drain caused by construction waste — not the owner's responsibility. Our legally valid survey report clarified liability and estimated repair costs at approximately HK$25,200, providing solid evidence for the owner to pursue recovery from the owners' corporation and the contractor.

SEWAGE BACKFLOW

SILVER SURVEYORS

10/29/20263 min read

Rooftop Construction Blocked Common Drain – Sewage Backflow Flooded a Home

Case Background

On 12 December 2025, the owner of Flat 7, 1/F, Block xx, Dragon Island Villa, Castle Peak Bay, Tuen Mun received a call — water was flowing out of his flat.

When he arrived, the scene was alarming. The kitchen and bathroom floors were covered in water, and the staircase landing outside his door was also flooded. The water wasn't coming from his own sinks or toilets — it seemed to be rising up from the floor drains and seeping in from outside the building.

Unsure of the source and unwilling to start repairs blindly, the owner engaged SILVER SURVEYORS to investigate.

What We Found On Site

We arrived that evening. Water was pooling on the kitchen and bathroom floors, and the staircase outside was wet. Looking up at the external wall, we could see moisture around the common drainage pipe running between the first and second floors.

The weather had been dry — no rain on the day of inspection and only 0.2mm in the previous three days — so external wall leakage was ruled out.

We used infrared thermal imaging to detect hidden moisture beneath the floor tiles, collected water samples for chemical analysis, and inspected the drainage pipe route from the rooftop down to the unit.

The Truth Emerged

The investigation revealed:

Significant trapped moisture beneath the kitchen and bathroom floors, plus the staircase area

Water samples tested as fresh water — no salt, no sewage content

The rooftop was undergoing floor works, and cement residue and construction debris were found inside the common drainage pipe

When tapping the pipe below the unit's floor level, a clear blockage was detected

The conclusion: this was not a leak from the owner's internal pipes or waterproofing. During rooftop construction, workers had allowed cement and building materials to enter the common drainage pipe. The pipe became blocked below the unit's floor level, leaving wastewater nowhere to go but back up through the owner's floor drains.

The Outcome

Our survey report provided clear, legally admissible findings:

The leakage was not the owner's responsibility — the source was a blocked common drain

Liability pointed to the rooftop contractor and the party responsible for maintaining the common drainage system

Affected area: approximately 70 sq. ft.

Estimated repair cost: approximately HK$25,200 (excluding damaged personal belongings)

With this report, the owner did not have to bear the cost himself. He could pursue recovery from the owners' corporation and the contractor, and use the report as supporting evidence for his insurance claim.

Our Takeaway

When water suddenly floods your home, the worst part isn't the mess — it's not knowing why it happened or who should take responsibility.

At SILVER SURVEYORS, we don't just find where the water came from. We help homeowners uncover the truth, clarify liability, and secure the compensation they deserve.

SILVER SURVEYORS – Leakage investigation service

We provide independent investigation and surveying services for all types of water leakage cases – including external wall seepage, upper-floor leakage, burst pipes, sewage backflow, ceiling dripping, and structural water ingress. Using infrared thermography, smoke testing, moisture metering, water sample analysis and other scientific methods, we accurately trace the source and deliver court‑admissible loss assessment reports. Whether it's a residential flat, shop or office, we help you get the facts straight, the numbers right, and the compensation you deserve.

Have a leakage problem? Contact Silver Surveyors. We'll listen to your situation first, then tell you what to do next.

📞 Inquiry Hotline：3489 9268 / 6608 4330

📱 WhatsApp：+852 5423 3828

🌐 Official Website：www.silversurveyor.org

📩 Inquiries welcome; free initial consultation.