According to NSW Building Commission research, 42% of recently completed strata buildings have serious waterproofing defects. Of buildings with any serious defect, 63% include waterproofing issues. It's the number one problem in the industry.
What makes waterproofing failures particularly costly is how they compound. A small leak doesn't stay small. Water travels, spreads, and damages everything it touches — and by the time the problem is visible, it's usually been developing for years.
Industry research suggests that repairing waterproofing failures can cost 10 times more than getting it right in the first place. Here are eight ways that small waterproofing issues become expensive problems.
Balcony waterproofing membranes have a limited lifespan. UV exposure, thermal movement, and foot traffic all contribute to degradation. When the membrane fails, water penetrates the concrete slab — often affecting the apartment below.
Early signs: Cracked or missing grout, tiles lifting at edges, water staining on the ceiling below. Cost if caught early: membrane repair, $5,000-15,000. Cost if structural damage occurs: full balcony remediation, $20,000-30,000 per balcony.
Bathroom waterproofing relies on the membrane behind and under tiles, plus sealant at junctions. Over time, sealant fails. Membranes can be damaged by renovations. Water finds its way through.
Early signs: Musty smell in bathroom, damaged paint or swelling in adjacent rooms, complaints from the apartment below. Cost if caught early: re-seal and minor repairs, $2,000-5,000. Cost if water has spread: full bathroom strip and rebuild, $15,000-30,000.
Flat roof membranes typically last 20-30 years, but failures can occur earlier — especially at flashings, penetrations, and drainage points. Once water gets into the roof structure, it can travel significant distances before appearing.
Early signs: Water staining on top-floor ceilings, increased humidity in top-floor units, visible membrane blistering or cracking on roof inspections. Remediation cost: $100-300 per square metre for membrane replacement, plus structural repairs if damage has occurred.
The junction between windows, doors, and the building facade is a common failure point — especially in buildings over 20 years old. Sealant deteriorates. Flashings corrode. Water enters the wall cavity.
Early signs: Water staining around window frames, mould growth on interior walls near windows, visible sealant cracking on exterior. Remediation can require full window replacement if original installation was inadequate.
Below-ground structures face constant hydrostatic pressure from groundwater. Waterproofing systems in basements and carparks are often minimal — and failures are common.
Early signs: Wet patches on carpark floors, efflorescence (white mineral deposits) on concrete, visible water ingress during rain. Remediation is often expensive because access is difficult and the source can be hard to identify.
Planter boxes on balconies and podiums are essentially permanent water sources sitting on the building structure. If the waterproofing fails, water continuously penetrates the structure below.
Early signs: Drainage problems in planters, visible moisture on adjacent walls, plant health issues suggesting drainage problems. Full remediation often requires removing planters entirely to repair underlying waterproofing.
Every pipe, cable, and duct that passes through a floor or wall creates a potential water path. Fire collars and penetration seals are designed for fire protection, but failures also allow water transmission.
Early signs: Water staining around pipe penetrations, drips appearing where services pass through structure. Often identified during fire safety inspections when collars are found to be damaged or incorrectly installed.
Small cracks in rendered or tiled facades allow water entry. The water sits in the wall cavity, causing internal damage that's not visible from outside. Over time, the problem expands.
Early signs: Hairline cracking visible on facade, especially around windows and at floor levels; internal moisture issues in units with affected external walls. Facade remediation on large buildings can cost millions.
The common thread: all of these failures are detectable early if someone is looking. Regular building inspections by someone who understands what to look for can identify problems when they're still manageable.
NSW law now requires waterproofing work over $5,000 to be completed by licensed professionals, and work over $20,000 may require Home Building Compensation Fund coverage. These protections help — but they only apply to future work.
For existing buildings, the key is proactive inspection and early intervention. Every waterproofing failure we've seen started small. The buildings that minimise costs are the ones that catch problems early.
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NSW Building Commission: Research report on serious defects in recently completed strata buildings (2023)
Fosroc: Waterproofing the #1 defect in NSW strata buildings — https://www.fosroc.com.au/news/waterproofing-no1-defect-nsw-strata-buildings/
ACIL Allen (2024): Waterproofing failure remediation costs research
Strata Plus: Waterproofing & Mould in Strata — https://www.strataplus.com.au/resource/waterproofing-in-strata/
Sedgwick: Cost to rectify water-related defects can be 10x the prevention cost
Dino Biordi
Founder & Managing Director, LUNA Management
25+ years in construction | NSW ABMA Independent Review Panel
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