Building constructions are a composite of complex components. As water ingress is amongst one of the most pressing concerns in the industry, waterproofing is a core component of a construction project.

Waterproofing Design

When designing new buildings, the structural design should consider the overall construction process together with a waterproofing design, as they interact & affect each other. For a building to permanently withstand water penetration, the fundamental issue is good waterproofing design.

Essentially, good waterproof design protects the structure from the penetration of water, thereby eliminating structural and aesthetic potential damage via water ingress.  Well-designed waterproofing together with correct installation and appropriate materials prevent water ingress into entire building envelope: internal and external, above and below ground, incorporating basements, foundations, balconies, planter boxes, terraces, roofs, and walls

However all too often little attention is paid to waterproofing design, as it is a construction component hidden and out of sight.  Failure to appreciate waterproofing and its function to protect a structure has resulted in catastrophic consequences.   Studies suggest that nearly 60% of all building damages and defects are caused due to water.

Water Ingress – Internal

Waterproofing is the combination of materials used to prevent water intrusion into the structural elements of a building or its finished spaces.

Once water enters an internal space, it can accumulate behind ceilings and walls which typically have high moisture concentration combined with lack of light. In such area’s moisture creates an environment highly suitable to encourage production of mildew and mold.

With time, mold and mildew can compromise not only the integrity of the building but impact the health and wellbeing of a building’s inhabitants and visitors.


Water Ingress – External

External areas of buildings such a balconies, terraces, basements, and roofs, need to have effective waterproofing to safeguard against damaging effects of weather and water. Waterproofing membranes play an integral role in enclosing and protecting external building surfaces.

If left unprotected, or poorly protected, external building elements become vulnerable to water penetration which in turn leads to the potential harmful effects to the fundamental integrity of the building.

External structures like balconies, roofs and terraces have finished surfaces such as screed, ballast or tiling which are designed to limit water penetration into the rest of the building envelope.  However, these finishes alone do not possess the ability to prevent water ingress completely. The waterproof membrane should do that

Surface Drainage

Waterproof design should also consider where and how to manage water flow.

When water falls on a surface it is either contained, distributed, or drained away. Balconies, decks, and external areas should be designed to provide drainage and surface falls to distribute water away.  If drainage is inadequately designed, or drains become blocked etc, surface water may “pond” or stand still.  Water may seep under the finished balcony surface, ie. under tiles and penetrate structural elements below. Over time water penetration will have aesthetic and damaging effects, and particularly significant if weight bearing structures are involved.

Waterproofing design must consider membranes to permanently stop water ingress, but also the movement, distribution, and drainage of water from surfaces.


Suboptimal Waterproofing Practices

Membranes refer to watertight materials laid over a surface to prevent water penetration. For instance, for balconies these membranes are applied either below finished tiles or above the structural slab in the case of flat roofs and terraces.

So many times, I have seen water penetration from an external balcony into a habitable room below. When taking up some of the tiles and removing some of the wall tiles & skirting we would often find that the waterproofing membrane was not turned far enough up inside the wall to contain the water. A perfectly good and expensive job rendered useless because an individual decided not to extend the membrane further up the wall. At junctions, membranes require turn ups, turn backs, and drip grooves to adequately control water.


Waterproofing Materials

Waterproofing membranes can be classified as sheet membranes or liquid applied membranes.

Membranes that can stretch and move according to the contours of the building, make an ideal solution for long term protection against water ingress. If the membrane is to be exposed to the sun, then it should be UV stable. The membrane should be flexible enough to take any shape it is laid over and be capable of turning up and over walls and other construction features. High-rise buildings benefit from the waterproofing applications that can stretch over future cracks that may develop.

Waterproofing membranes also demonstrate potential in metal and steel components of a building to prevent water leaks.

Liquid-applied systems offer important advantages over sheet and roll products, they provide seamless protection across the surface and seal difficult areas like around multiple penetrations, skylights, gutter ways, fountains and behind indoor tile. They also eliminate the time and expense of installing flashing and termination bars.”

Because these membranes are applied as a liquid, they’re monolithic (no seams) and are typically considered self-flashing, so it’s an excellent choice for external structures with difficult flashing details. The lifespan varies, depending on conditions and materials, but is typically about 25 years.

Waterproofing often possess beneficial properties such as tear resistance and breakage, as well as the ability to release water into the atmosphere in vapour form to lengthen the life of the structure.


Concrete & Waterproofing

Form defects, imperfections, honeycomb, shrinkage cracks and numerous penetrations all add up to one thing, concrete is not a reliable water containment.  Concrete can be made to be waterproof, however unfortunately concrete very rarely is waterproof. Concrete structures are often affected by water penetration problems. To name just a few like Cold joints c& expansion joints are a major water entry point even in vertical surfaces. Beam and column ties can also be a point of water penetration.

Waterproofing design involves those who have a responsibility to ensure a construction project is made watertight and perform as such for a given period (min 10 years).

The industry needs to consider the contribution of waterproofing as a vital component in the design, planning and construct of our buildings. Waterproofing design affects building quality and the longevity of structures.


Article by Paul Evans 

President – Australian Institute of Waterproofing (AIW)  

Registered Victorian Building Practitioner (RBP) – Building Practitioners Board License CBU-4077 & DBU-7983  

Master Builders Association Victoria (MBAV) Specialist Contractor – License 094507  

Managing/Director - Findlay & Evans Waterproofing  

Telephone: (03) 8812 2918  




Australian Institute of Waterproofing (AIW)

Contact Details: 

Address: 155 Barkly Ave Burnley Vic 3121 

PH: 1300 249 466