Waterproofing

Leaks, which may not become apparent for some time, often only occur after a building is occupied. In many cases they are difficult to trace and may involve considerable cost to rectify. They are also a major cause of frustration for building owners with contractors often attempting quick-fix solutions rather than undertaking the work necessary to rectify the underlying or root cause problem.

Problem areas include roofs, basement walls, verandahs, raised planters, green roofs, decks and wet areas. The building must prevent water from causing unhealthy conditions due to dampness for the occupants, also deterioration of building elements.

Water is to be collected, redirected and drained to the appropriate outlets. Failures of waterproofing systems are due to poor documentation as well as poor construction.

The onus is on the design team to ensure water is directed away from the building. Full documentation is to be provided to communicate water shedding details, for instance slabs to be built with a fall need to be drawn and modelled with a fall, not just an arrow noted ‘fall’. Good practice suggests that the National Construction Code (NCC) requirements and the manufacturer's recommendations are transferred to the construction details, so there can be no doubt how the work is to be undertaken. Referenced details in the NCC or from the manufacturer's guides may not be well understood by those constructing the work or by the inspecting architect. Where the detail is available in the drawings it is more likely to be followed and those inspecting the work have a much better chance of identifying non-conforming work.

Some contractors require fully warrantied systems to be used. For example: the whole system (waterproofing, screeds, etc) should be worked through with the one supplier and they provide specifications and warranties for the whole system from bottom to top, outside to inside or relevant application.

Standard details, which have been proven on other projects, should be repeated and where new materials or technologies are being used for the first time they should be thoroughly investigated and the details developed in conjunction with the manufacturers or specialist consultants. Details should illustrate the difficult junctions, not just the easiest. Architects should ensure that a list of accredited installers are referenced in the specification to ensure a high standard of delivery.

Architects should also make sure that the key waterproofing activities such as waterproofing membranes and roofs are inspected before they are covered up or scaffolds are removed, making inspection difficult.

Waterproofing Standards

There are a number of Australian Standards providing guidance on the appropriate design methodologies required to achieve compliant waterproofing, including:

• AS 3740: Waterproofing of domestic wet areas
• AS 4654 suite: Waterproofing membranes for external above-ground use
• AS/NZS 4858: Wet area membranes

Further resources:

• For information on the NSW Design and Building Practitioners (DBP) Act and Regulations, please refer to our dedicated Institute page.
• Waterproofing in buildings: preventing leaks and Lawsuits (Available via Online CPD)