Waterproofing in residential buildings has traditionally been considered in isolation. Experts say a more holistic design approach is needed to prevent problems and catch issues long before construction begins.
Flammable cladding and cracks in buildings often make headlines, but waterproofing is the most common defect found in class 2 residential apartment buildings in New South Wales.
This is according to a survey of more than 1400 strata managers across the state conducted by the Office of the NSW Building Commissioner and Strata Community Association NSW. The survey found waterproofing defects were likely to affect 23 per cent of all buildings.
Greg O’Mara, Principal Compliance Officer, Building and Construction with the NSW Department of Customer Service leads a team that conducts audits of class 2 buildings.
He has seen a range of waterproofing issues since starting his role in August 2020.
“We identify problems or potential issues with documentation and check for compliance,” O’Mara told create. “We’re looking primarily for what we classify as a serious defect.”
Serious defects include defective design, defective or faulty workmanship or defective materials, and a failure to comply with the performance requirements of the Building Code of Australia, the relevant Australian Standards or the relevant approved plans.
O’Mara said it was rare to find problems with a design, particularly since the Design and Building Practitioners Regulation came into effect in July 2021. This requires designers, engineers and builders who work on apartment buildings to be registered, and states that building work cannot begin until regulated designs and compliance declarations have been lodged on the NSW Planning Portal.
Instead, it is usually in the execution of a design that problems occur.
“Across the board, the designs are usually okay,” he said. “We find a big problem when it comes to execution. You have a design, you just haven’t followed it.”
O’Mara pointed to an example of an apartment block with marble tiled bathrooms and high-quality finishes. Although everything looked good on the surface, underneath it was a different story.
“When we reviewed photographs of the wet areas in the bathrooms under construction, we found major faults,” O’Mara said.
“While we could see a great level of care had gone into the application of the waterproofing membrane, we noticed that the product on the floor was one colour and the product on the walls was a different colour.”
An inquiry to the builder revealed waterproofing products from two different manufacturers had been used in the bathrooms.
The team also noticed the wall linings weren’t fixed with screws but had been glued on, meaning the substrate would eventually fail under the weight of the tiles.
“Although the level of workmanship in terms of the waterproofing application was some of the best we’ve seen, they used the wrong products,” O’Mara said.
“Plus, no matter how good the waterproofing is, if the substrate fails, the waterproofing is not worth anything. The result was the developer pulled out all the bathrooms and started again.”
A more holistic approach to waterproofing
Many waterproofing issues stem from the fact it has traditionally been viewed in isolation from the broader building design. This means there has been little consideration given to how a waterproofing membrane will interact with adjoining sections of a building, or the impact of building deflection on drainage.
This lack of integration needs to change, said Engineers Australia Fellow and Chartered engineer Michael van Koeverden FIEAust CPEng, Director of CQT Services.
A past President of Engineers Australia’s Newcastle Division and ast National President of the Concrete Institute of Australia, van Koeverden is Engineers Australia’s representative on a committee convened by the NSW Building Commissioner to improve waterproofing practices. The group will produce technical specifications for waterproofing and development of a formal waterproofing qualification.
“The reason it’s become so apparent that training is needed is because of the extent of water damage in new buildings, and the way waterproofing has been treated in the past,” he told create.
“In many cases, people consider a waterproofing membrane to be a waterproofing solution. We are moving towards a more holistic approach and a new definition of waterproofing, where it’s the collection, redirection and drainage of water, rather than just the application of waterproofing membranes.”
A more integrated approach is also important as the standard for concrete structures (AS 3600:2018: Concrete Structures) requires a design life of 50 years, while waterproofing membranes can last as little as 10 to 15 years.
“We have a potential disconnect between the waterproofing provided by the membranes and what the structure is required to do,” van Koeverden said.
“Future designs will be required to nominate 10-year deflections, joints will need to be identified clearly on drawings in terms of what their role and function is, and part of the engineers’ responsibility is to provide a design that’s capable of meeting the requirements for waterproofing.”
O’Mara said a coordinated approach would help mitigate some of the more common waterproofing issues his team sees. For example, cantilevered balconies where stormwater drainage is embedded in the slab.
“We’ve seen a case where the balcony is deflected to the point where, structurally it’s no problem, but [the water] that would once fall towards the drainage outlet now falls to the outside edge,” he said.
“That’s an example of not enough coordination in design … We need to make sure the structure is involved with the drainage, with the waterproofing, with the facade. It should be holistic rather than individual silos doing their own thing.”
For van Koeverden, improving waterproofing is ultimately about providing the best solutions for the community.
“As professional engineers that is one of our goals — to act in the best interest of the community we serve,” he said.
“We need outcomes that the community can be proud of, and we as a profession can be proud of. Not only in terms of creating areas that people want to live in, but also … providing high-quality buildings that will last long into the future.
“That’s the big thing for me — ensuring that people who are involved in these designs and in construction understand they have a responsibility to deliver quality designs and structures.”