Sub-grade structural waterproofing has become a serious issue in the Australasian construction industry. This article does not pretend to be a definitive or exhaustive dissertation on the topic. We would simply like to review some key points that should be considered in context, and given upcoming changes to the NCC in 2025.
There is no Australian or New Zealand standard for sub-grade waterproofing. By default, British Standard 8102 has been referred to by construction designers for many years. BS8102 underwent its most recent revision in 2022.
Assessing levels of risk
One of the core guidelines in the Standard is the grades of environment.
- Grade 1A – Seepage Acceptable, i.e. water ingress – for example a low-grade car park
- Grade 1B – No seepage / water ingress, but dampness within the structure is accepted. A typical car park would adopt this level.
- Grade 2 – No seepage, dampness acceptable only as a result of condensation. A plant room could handle this level of environment.
- Grade 3 – No seepage or dampness acceptable. This would be the requirement for a habitable area.
The term ‘dampness’ strictly refers to internal moisture created within the structure by condensation and similar. Any moisture penetrating from the outside is classed as ‘seepage’.
Grade 1A basement structures are commonly known as ‘wet wall’. This low level of protection is not recommended. Indeed in Australia the impact of the drained water on council infrastructure has led some councils to actively decline such systems in new builds.
It is worth mentioning shotcrete construction at this point. The sheer difficulty of providing consistency in shotcrete application means that it cannot be relied upon to support the waterproofing of the structure.
Waterproofing protection types
We then come to the different methodologies used in response to these risk levels.
- TYPE A: Barrier protection – bonded membranes.
- TYPE B: Integral Protection – such as admixtures.
- TYPE C: Water management system – drainage.
These are reasonably self-explanatory. Type C, drainage, is the response to Grade 1A structures, i.e. wet walls. As discussed above, this low level of risk mitigation is not recommended.
Type B, integral protection such as admixtures, will often be adequate for Grades 1B and 2. There are other factors to be considered, however, such as the construction method, and the height of the water table.
Type A, bonded membranes, would usually be required for Grade 3 structures. Indeed, for the highest protection, and in high-risk projects, a combination of Types A and B should be used: membranes plus admixture.
The risk level and requirements for each project must be specifically assessed; a cookie-cutter approach is not acceptable. Joint design and gasket placement also become very significant.
De-Risking from the outset
For any such project, it is critical that a waterproofing specialist is appointed from an early stage, and intimately involved in the design process.
Initial design concept – the building is devised around certain needs, commercial considerations, and land available.
Structural design considerations – what will this concept involve? The footprint, volume and envelope of the structure will impact the risk level. The site needs to be assessed for water table height and any other geological risks.
The client’s requirements – what factors around the practical requirements and use of the building, will affect the waterproofing risk?
Hence the importance of appointing the waterproofing specialist early in the design process. They can draw these elements together before any design is committed to.
A desktop study will give shape to the overall project and identify risks which may or may not have been considered.
The process will result in a practicable design, with risk identified and avoided or mitigated as part of that process.
Waterproofing type/s can then be selected.
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CSSW Certification and other accreditation
In the UK, a structural waterproofing specialist should carry CSSW certification: Certificated Surveyor in Structural Waterproofing. The CSSW certification is a professional qualification for individuals involved in diagnosing defects connected to water entering structures below ground level and who recommend design solutions.
Within Australasia, you should certainly ensure your specialist has appropriate levels of professional indemnity. If you have access to a CSSW certified expert, they will be able to offer key and relevant assistance.
Other factors include a system warranty in the installed system – not just product replacement; tightly controlled quality assurance; and environmental impact provisions.
Overall, the message is this: de-risk from the very start, using professional specialist guidance. British Standard 8102 remains a distinct influence within Australia and New Zealand.
A recent webinar featuring industry experts from both UK and Australia is available here.
Questions? Like to discuss an upcoming project? We’re keen to hear from you.
