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Waterproofing 101: How to Get it Right

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Recent Deakin University research has found defects involving waterproofing are one of the major issues for Australian buildings. The research study focused on multi-residential buildings and included an in-depth examination of 212 building defect audit reports from Queensland, Victoria and New South Wales for buildings completed over the past decade.

The researchers also interviewed owners, building managers, and industry stakeholders.

According to the study funded by the PICA Group, water damage was the biggest problem in apartment buildings. Water ingress and moisture accounted for 29 per cent of defects impacting the buildings, and waterproofing as a distinct building system was defective in more than one in ten cases.

“Of the 3,227 defects analysed, defects relating to building fabric and cladding were the most prevalent, followed by fire protection, waterproofing, roof and rainwater disposal, and then structural issues,” said lead researcher Dr Nicole Johnston, a senior lecturer in Deakin Business School.

“It is important to note that of the defects coded to building fabric and cladding, one-third were a consequence of water penetration or moisture.”

Membrane-related defects were the most common waterproofing defects reported. Balcony areas comprised 28 per cent of reports, internal wet areas 19 per cent and with podiums, windows and doors, caulking seals and planter boxes also mentioned often.

Of the defects coded to building fabric and cladding, one-third were a consequence of water penetration or moisture.

When asked about causes, interviewees suggested human error, misuse of products, poor workmanship, time pressures, poor supervision, lack of training, and lack of licensing of the relevant subcontractor.

“A number of concerns were also raised about the relationship between the National Construction Code and the Australian Standards, where there is some disconnect in requirements, and industry identified a need for better consistency,” Dr Johnston said.

“The focus on minimum standards instead of best practice in the National Construction Code was also raised as a concern, as well as the private certification system, where community expectations were seen to be out of step with legal requirements.”

The report also flagged the impact water damage has on owners and residents. Mould growth due to water penetration, for example, can have major health effects.

“And for lot owners, there are also financial impacts,” she said. “The type of defects we commonly observed require invasive and often costly remedial works to rectify, particularly for waterproofing and fire separation failures.”

The report recommends stricter oversight and regulation to ensure waterproofing meets the required standard.

During a recent review of Victorian building regulations, the Australian Institute of Waterproofing asked the Victorian Building Authority to consider introducing inspections as a measure to correct the chronic rate of waterproofing failures. However, the change was not introduced, leaving the builder responsible for signing off on the Compliance of waterproofing with the relevant provisions of the National Construction Code.

Secretary of the AIW, David Hepworth told Jobsite that the two most common locations for waterproofing defects are external balconies and internal bathrooms.

He said the reason defects are so common in multi-residential project bathrooms is a failure to follow the National Construction Code and comply with the specific Australian Standards referenced in the Code. There is a similar problem with balconies, he added.

Cost and time pressures which are passed from builders onto subcontractors are also a factor, he explained. Sometimes, people simply take shortcuts.

Hepworth also said there are not enough inspections, and that they are often a case of “compliance by paperwork, not by observation.”

One of the ways builders, project managers and site supervisors can mitigate this situation is to carry out their own inspections of waterproofing before moving on the next stage of works, such as tiling.

Hepworth said taking a photo of the waterproofing is valuable. It can serve as documented proof waterproofing was completed to the standard. As some defects are caused by subsequent work post-completion or by failures in a maintenance practice, it also protects the builder from unfair blame or potential legal liability.

Builders should “get familiar” with the relevant standards for waterproofing of internal bathrooms and external balconies.

He said builders should “get familiar” with the relevant standards for waterproofing of internal bathrooms and external balconies.

There are also other parts of the construction process to which builders, site supervisors and project managers should be paying greater attention. Faults in expansion joints, window caulking, rainwater harvesting systems, guttering, facades and roofing can all contribute to water ingress or moisture issues, according to the Deakin research.

For balconies, AIW President Paul Evans has noted that lack of appropriate expansion joints in tiled areas can lead to failure of even a compliant waterproofing membrane. As tiles expand and contract during weather extremes, the membrane may tear.

Moreover, it is important builders look for an experienced waterproofing subcontractor, Hepworth said.

While ensuring work meets the standards will reduce defects, Hepworth believes any builder aiming for best practice should strive to exceed them. If the standard requires waterproofing of a specific area of floor relative to a drain, he suggested doing the whole floor instead. For showers and walls, where the standard requires one metre of waterproofing from floor level, doing the whole wall is also an option.

He said the increase in materials costs and time is negligible, but the outcome is a much better product. Waterproofing is only around one per cent of total project costs. However, if defective, it can be responsible for approximately a third of the cost of any defect rectification works.


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