May 2024 Leakfix Newsletter: Overcoming Waterproofing Challenges in Modern Construction
Owners Insights: High Performance buildings - how to make them work in a framework of Australian NCC?
1. BASEMENTS
We were recently engaged by Client to compile a “Waterproofing Performance Solution” for a project involving construction of 2 structures, a Class 1a building (as per NCC Classification) and a Class 2 Apartment Building with 2 single level Class 7a buildings for a basement.
Navigating the compliance pathways, we initially suggested using a Performance Specification as a Performance Solution for basement waterproofing. This mainly due to lack of DTS provisions for below-ground waterproofing and the nature of the underground structure. We assessed the site conditions and suggested using British Standard BS8102 as a reference for developing the waterproofing performance specification.
It is important to note that we did not claim full compliance with the standard; instead, we incorporated its design philosophy to propose waterproofing performance that was deemed appropriate by the building owner. By the time we were involved, much of the structural design was already completed. The client was eager to submit the application for CC1, consequently, we adapted the waterproofing to fit the pre-existing design, making minor adjustments to ensure the desired internal grade of waterproofing performance can be achieved.
Basement Waterproofing Design by Architect in this case was technically a Performance Solution to exceed Performance Requirements in NCC, not a mandatory compliance requirement but merely an attempt to exceed the minimum requirements imposed by the NCC and council.
Given upcoming changes to NCC (2025), it is wise to adapt overall basement design strategies to align with new objectives. The earlier you engage a Waterproofing Specialist, the better outcomes you will generally get. Ideally a Waterproofing Specialist should be involved before structural design is in place and not the other way around, as it is almost always required to alter parts of structural design to integrate it with the waterproofing strategy.
Waterproofing Specialist can be anyone with sufficient knowledge and experience. I personally have passed my CSSW (Certificated Surveyor in Structural Waterproofing) certification in order to be able to provide my clients with adequate support while they are developing their basement waterproofing designs.
We think that for waterproofing design a simple performance objective could be used. The structure will be watertight below ground or it won’t be. Suitable performance should be decided based on the intended use of the structure. Structure should be either tanked or drained depending on ground conditions. If the structure is drained, suitable provisions should be made to avoid water under pressure building up against the structure for the design life of the structure - this should be taken seriously. Maintenance plan should always be prepared by a suitably experienced person. We think that in high risk scenarios no modular construction should be used below ground level. However in some cases if risk is deemed low, and dampness in the space tolerable and can be controlled with regular maintenance, we think that perhaps it is appropriate to use such a modular approach.
📨Give Jakub a shout if you feel like you need specialist advice for your basement
waterproofing.
2. ROOFS, TERRACES, BALCONIES
We at Leakfix do care about the environment and we think that in order to build more sustainably, drastic increase of energy efficiency of structures is required, this however brings all sorts of challenges related to sealing the building envelope and moisture control of the internal environment.
In order to achieve our energy efficiency goals the use of more insulation in the building assemblies is unavoidable. This inevitably makes the fabric of our structures thicker, more complex and in effect more expensive to engineer and verify.
For flat roofs (or low slope roofs) from insulating point of view, there are 3 most common types of assemblies:
2.1 Warm Roof
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| Figure 1 |
2.1.1 The obstacles.
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| Figure 2 |
- Conflicting and incompatible NCC DTS provisions - in a nutshell, Part F is not entirely compatible with Part J anymore - Performance Based Designs are needed.
- Widespread lack of understanding on how to treat these high performance assemblies by all building disciplines consultants.
- Lack of sufficiently skilled trade people to facilitate installation of such assemblies.
- Uncertain future of this solution in the face of upcoming NCC changes.
2.1.2 Prognosis
Despite complicated compliance pathway, warm roof assembly is the most efficient and practical to use in most cases where flat or low slope roof is proposed. If NCC 2025 imposes the new requirements for the falls being in structural substrate, this assembly will be in effect outlawed.
In order to make this assembly work better in Australia, an innovative performance based approach is needed. Due to complexity and very often a custom nature of required solutions, an adaptable verification method is needed to determine watertightness of the assemblies. In our opinion this is very much an achievable alternative for the compliance pathway. If a waterproofing assembly can be designed as “hydrostatic” (capable of being watertight even under pressure), it can be said that there are a variety of testing methods available on the market to verify such “watertightness claim”. Each system should be engineered to suit site specific conditions, unfortunately Deem To Satisfy Pathways no longer seem practical and will cause widespread confusion amongst the designers wanting to utilize this design in their building.
2.2 Inverted Roof
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| Figure 3 |
2.2.1 The obstacles.
- It is hard to make this design compatible with all of the other design objectives,
- It works best when ballasted/buried,
- Often insufficient R value to meet the requirements,
2.2.2 Prognosis
Due to the low thermal efficiency of this assembly, it will likely be abandoned for above-ground construction unless technological advancements occur.
This buildup undeniably presents a lower waterproofing risk for below-ground construction made of concrete. This approach will not work for lightweight construction often used above ground level. While it is technically possible to lay timber and other lightweight substrates to falls, it is neither easy nor practical, especially in large-scale multi-residential projects.
2.3 Cold Roof
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| Figure 4 |
2.3.1 The obstacles.
- Sealing the thermal envelope is complicated in this arrangement
- High risk of condensation in the cavity exists is most cases
- Given the fact that multi residential structures are built for profit, it doesn't seem to be feasible to increase or decrease the height of the building to accommodate the space required for this buildup,
2.3.2 Prognosis
While still not an ideal solution, it is widely used in residential pitched roof construction, where it is somewhat more practical. We at Leakfix are of the opinion that this assembly should not be used for flat or low slope roofs assemblies above habitable spaces, mainly due to risk of condensation.
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