Despite being one of the most important factors to the longevity and integrity of a building, tanking is often the epitome of ‘out of sight, out of mind’.
However, since areas-built underground are more prone to water ingress, ignoring or underestimating the importance of using the right waterproofing methods in modern construction could lead to more severe problems.
There are three types of tanking systems: Type A, Type B, and Type C.
Type A systems rely on a membrane applied to the exterior of a structure to prevent water ingress, while Type B systems are integral to the structure itself (such as specifically designed, waterproof concrete).
Type C systems, however, manage water that has entered the building and then remove it through a controlled internal drainage system.
Depending on the building, either Types A or B are considered essential, with Type C used as a contingency in new builds or a remedial solution for existing buildings.
Despite the global application of Type C as a crucial component for high-risk areas in new builds (in conjunction with either Type A or B), New Zealand has been relatively slow in embracing Type C tanking systems.
In New Zealand, Type C is typically only considered when the existing Type A or B systems fail. This failure can occur due to a range of reasons, including poor quality workmanship to a change in the function of the space (for example, transforming a storage basement into an electrical room, which demands a drier space).
This raises a critical question: Is New Zealand falling behind in adopting the most current and effective standards in construction?
The only remedial option
In short, because tanking is underground, once a building is built, there are limited repair options you can do to a Type A or Type B system if they have issues or start to fail.
The good news is that Type C can be retrofitted to a building to deal with the water ingress.
While it is, obviously, cheaper to have installed Type C when the building was being built – particularly if it has areas that can’t risk having any water in them – Type C is usually the only remedial option you have available. The alternative is to tear the building down and start again.
Additionally, as we’ve seen in heritage projects like the Sofrana Building in Britomart, if a building’s use changes, so too can the waterproofing requirements.
During a refurbishment of the building’s basement, there were unexpected issues with water vapor from the floor. This problem was due to unusually high-water table levels and external structural excavation.
The building’s base slab lacked structural integrity, making it impossible to bond any coatings directly to it. Additionally, there wasn’t enough height space to pour a new slab over the existing one. In this situation, our team applied the Newton System 500, a Type C waterproofing solution.
It works by creating a controlled drainage path which prevents water from penetrating internal spaces, effectively mitigating the risk of dampness and structural damage.
Placed directly on top of the existing surface and covered with a screed, it allows for future flooring installation. This system effectively prevented moisture from getting in and ensured the interior space remains dry.
Another factor causing the need for a contingency system is future neighbouring construction that changes the groundwater levels. Sooner or later, this is going to negatively affect the efficiency of your Type A or B tanking system. Unless, of course, you have installed a Type C that allows for all groundwater conditions up to ground level.
Getting it right from the start – Type C in new builds
For new builds, the cost of implementing a Type C tanking system is similar to that of Type A.
Type C is not used alone and always accompanies another system, choosing it from the beginning essentially doubles the initial cost – which is often why it is not included in the design phase.
However, this is a short-sighted view when you consider the potential future cost of water damage to your building. Couple this with the cost, possible complexity to retrofit with Type C, and the disruption to the building’s occupants during the remedial work, and the overall cost could be uncalculatable.
Looking at it like that, Type C is an extremely worthwhile investment to protect your building, ensure its longevity, and prevent costly maintenance and repairs.
And, speaking of maintenance, Type C is the only tanking system that is able to be monitored and maintained for the life of your building. As an example, the vents or outlets of the Newton System can simply be flushed with a hose, before returning to normal functionality.
The future of waterproofing in New Zealand
Currently, New Zealand has no formal underground Code of Practice. Our tanking guidelines are not clear on which type of system should be applied to which type of new building.
In general, we follow the British standard, which was recently updated at the end of 2022. That code now specifies that any habitable space underground requires two forms of waterproofing. It’s not yet law here, but it is sensibly starting to become more and more common on building specifications.
Changes in the UK have mostly come about due to the involvement of insurance companies in the legislation. Given that New Zealand is a country prone to weather events and seismic shifts, the chances of similar concerns being raised by our construction insurance industry are increasingly likely.
To date, Type C remains largely unknown to architects or building consent authorities as it’s mainly introduced at remedial stage.
As the industry becomes more aware of international best practices, and the benefits of introducing it as a contingency in the beginning, we hope to see Type C become a standard requirement.
Do what’s best for your building
In summary, speaking from our 47+ years of experience, the combination of Type A and Type C is your best bet to ensure a fully watertight building. The addition of a Type C tanking system during a new build is the most modern, forward-thinking method, and one that New Zealand would benefit hugely from adopting consistently.
As tanking specialists, there isn’t anything we haven’t seen and can help you select the right tanking system for your building.
When it comes to installing Type C in new builds or as a remedial solution, we’re industry leaders and are Approved Installers of Newton Systems.
So, get in touch to start the conversation.