Water leaks are not always from faulty membrane

19 January 2021
By Simon

Over the years we have talked extensively about water leaks and the issues they cause. We have detailed the role of a good membrane, of having good waterproofing and even the need to ensure you maintain your drains and down pipes. But one thing we have neglected is the role of cavity flashings.

Flashings are used across industrial, commercial, multi-dwelling apartment buildings and single-dwelling homes and are a requirement for complying construction. But whilst they may be required, it does not mean that they are always installed correctly, or that over time they have not broken down and now the cause of your water ingress issues.

In this article, we explain the role of cavity flashings, explore issues which can come around from their failure and other interesting information which will help you see the importance of a complete waterproofing system.

The problem with water leaks

To simply say that water ingress is bad news is an understatement. Water ingress in buildings can cause immediate damage (carpet, electrical or other damage) and ultimately lead to hefty rectification costs involved with detecting leaks, rectifying the cause and then taking steps to remedy the situation (which the longer it goes on, will cost more to fix).

And if you do not believe us, then let us share this: Based on statistics, 80 percent[1] of building defects are attributed to water leaks and consequential damages yet water proofing only accounts for just 1 percent of the building costs. According to a study conducted by University of New South Wales (UNSW) City Futures Research Centre, waterproofing is listed as the foremost problem in newly build apartments in Australia.

And here is the thing, even mild water ingress may cause ongoing issues when the water or moisture comes into contact with areas of vulnerability such as electrical and communication wires, plasterboard or internal surfaces including carpet. Furthermore, as we have spoken about at length, water issues will ultimately lead to structural issues, and can also increase the risk of pest and health issues caused by mould and damp. Fixing any of these issues (notwithstanding fixing the structural issues) can cost tens of thousands of dollars.

So what else do you need to know? Well here are a few pertinent points to consider.

What you need to know about Flashings

Compliant to Performance Requirement P2.2.2, the roof and external walls of a structure must prevent the entry of water that could lead to unhealthy or dangerous conditions, a loss of amenity for residents, and undue dampness or deterioration of the elements in the building. Flashings should be installed in masonry to function as a barrier to water penetration or seepage, and redirect moisture which would otherwise get into the building. Flashings should be either partially exposed or embedded, and made up of metal (lead, aluminium, copper, zinc) or non-metal (rubber, plastic).
Flashings are typically utilised on roofs around projections or intersections, wall interruptions such as windows, under sills on windows or door thresholds, intersection of roof and wall, through-wall or cavity wall, lintels above doors and windows, edges of roof, junctions on slope, pipes penetrating roofs, and at the intersection of two (2) roof planes forming a valley in which water may pond. In other words, it should be anywhere where there could be a weak point in the building structure due to a change in plane or material.

Cavity flashings (which can be thought of as through-wall flashing) are a continuous sheet of impervious material installed across gap of the wall, that redirects moisture that may enter the wall towards the wall exterior to keep the building structurally intact. It is applied to all points where moisture may enter the wall and in select places susceptible to water infiltration.
Weep holes or head joint vents often accompany (we believe they should always be present, though many builders neglect this simple and effective measure) through-wall flashing to formally permit water egress. This type of flashing is required to span from a minimum of 200 mm from the low point of external wall to the high point inside the wall. Weep holes are spaced typically at 600 mm centre to centre throughout the wall length allowing moisture an easy way to exit the building especially if one of them should be blocked.

Factors which affect the performance of Flashings

If you have water ingress issues, you may benefit from checking/installing your flashings. But before you do go and install new/replacement flashings, there are a few things to consider which are stipulated in the Building Code. Factors including design, materials selection, installation and maintenance will affect the efficacy of the flashings you install.

Materials and component compatibility.

When you are installing flashings there may be other metals in the area you are looking to install them. When exposed to water and other metals, metal flashings may cause undesirable chemical reactions. Make sure you check for other elements, and where possible, ensure flashing materials and components are acquired from a single manufacturer.

Limits of application

Compared to trimmed flashings, extending the flashing beyond the face of the wall improves overall drainage. However, as with all things, More is not always better, so check that you ensure your design is not over the top.

Adhesion to substrate

There is no use installing your flashings if they are not adhered adequately. Make sure you have full adhesion to the substrate material which prevents lateral movement.


There will be instances where you need to overlap the flashings. Where this occurs, ensure you overlap the flashings by at least 150 mm to the substrate and ensure you seal the edges. Sealant recommendations from the manufacturer should be sought to protect edges of splice.

Continuity to corners and projections

Where you need to add bends or corners, try to source prefabricated pieces as these improve the performance of the flashing. Where this is not possible, make sure you overlap all cuttings and adhere them adequately.


An end dam of at least 25 mm to head joint should be constructed where flashing is not continuous, such as on openings and sides of vertical expansion joints. Flashings should be integrated with water-resistive barriers to enhance drainage. Any flashing can be terminated at the bed joint of a wall interior and termination must be held in place.

UV exposure

Flashing materials should withstand exposure to sunlight, and not lose desirable physical properties.

Don’t be wet behind the ears

What we are trying to say is, don’t take shortcuts. Shortcuts in the building and maintenance process inevitably lead to both short and long-term issues which end up costing building owners much more than you may think. When it comes to flashings – whether the installation of new or the rectification of existing ones which are not working as expected – ask a professional. We have a team of experts on hand to help identify your issues and provide a course of action to help you rectify the issue. If you need more information, call the Remedial offices today.

[1] https://www.architectureanddesign.com.au/suppliers/projex-group-1/waterproofing-tips-for-commercial-property-owners