C. Common causes of water seepage

C. Common causes of water seepage

Water seepage is commonly attributed to maintenance failures, structural defects, or poor workmanship in multi-storey buildings. 

Defective piping and drainage systems 

A frequent cause of seepage is a leak from water supply or drainage pipes located in floor slabs or wall voids of upper or adjacent flats. 

• Fresh and flushing water: Leaks may originate from fresh water supply pipes or saltwater flush systems. Burst pipes, including those located in communal water meter cabinets, can cause sudden, serious flooding that damages common facilities like passenger lifts. 
• Drainage and sanitary fitments: Defects in drainage pipes, such as those serving kitchens or bathrooms, as well as leaking sanitary fitments like toilet bowls or washbasins, are common culprits. 
• Concealed and re-routed pipes: Problems often arise from pipes buried deep within concrete slabs or those that have been re-routed during renovations. If these pipes are not properly installed or have aged, they may leak through small cracks even when the main supply is turned off. 

Waterproofing and sealant failures 

The deterioration of protective barriers is a major factor in persistent seepage cases. 

• Waterproofing membranes: Deteriorated waterproofing layers in floor slabs, especially in “wet areas” like bathrooms and kitchens, allow water to migrate to the unit below. These membranes typically have a lifespan of 15 to 30 years, making older buildings more susceptible. 
• Sealants and joints: Seepage frequently stems from defective bathtub sealants, worn-out silicon seals, or failing shower tray waterproofing. 
• Sunken slabs: In many Hong Kong buildings, bathrooms are constructed with “sunken slabs” which can collect and trap water if the waterproofing is defective, acting as a conduit for water to travel horizontally before seeping through the ceiling below. 

External and structural factors 

Environmental conditions and building maintenance play a critical role in seepage through the building envelope. 

• Rainwater ingress: Rainwater can penetrate through defective roofs, flat roofs, external walls, or balconies. This is often due to cracks in external concrete or the natural wear and tear of the building’s outer finish. 
• Expansion joints: In structural contexts, the ageing of expansion joints between different parts of a building (such as between a rooftop and a residential block) can become a conduit for water. 
• Window and A/C openings: Seepage may occur through defective window frames, damaged weather gaskets, or gaps around air-conditioner installations where sealants have failed. 
• Maintenance neglect: A specific cause noted in several cases is the blockage of roof drain holes by debris or fallen leaves, which causes rainwater to overflow and seep into internal areas or staircases. 

Condensation and specialised causes 

Dampness is not always caused by an active leak but can result from environmental physics. 

• Temperature differences: Seepage-like dampness can be caused by condensation arising from extreme temperature differences between units, such as a cold server room located adjacent to a standard residential flat. 

• Construction and renovation mishaps: Sudden seepage can be triggered during building works, such as when contractors remove existing waterproofing membranes for repair but fail to provide adequate temporary protection against rainfall. Additionally, drilling holes into a ceiling or floor slab to fix structures (like solar panels or ventilators) can loosen or damage existing waterproofing layers, leading to new leaks.