Whether it’s caused by free water or high humidity, prolonged dampness in buildings can result in mould and decay, deterioration of internal finishes and even pest infestation. In fact, numerous studies – including one by the University of New South Wales – corroborate that there is a high proportion of water penetration issues causing damage to buildings.

Paul Ratcliff – a building consultant with over 30 years of experience and an excellent grasp of what makes building structures work and fail – thinks that a lot of it comes down to the fact that there is still not enough education around how to control moisture in buildings in the industry.

And with a plethora of multi-residential and high-end commercial projects under his belt, there is no doubt he’s the expert on the matter. “I can walk through the door and be able to tell right away if the house is suffering from bad dampness issues,” he reveals. “In fact, just standing in the street, I can give you the variables that will affect it. Considering the way the house is orientated; where the soil is around the site relative to the external walls, and where the planter boxes are relative to external walls and habitable spaces. It's all a risk.”

Paul says that the first thing good design needs to do is to identify these risk elements and try to reduce them so that in the event that something goes wrong that it's not going to affect habitable spaces. “In my experience as a building consultant, moisture control, water entry prevention and condensation in buildings are incredibly important,” Paul sets out the basics. “And to be successful in moisture control, you really have to keep the building dry and well-ventilated as possible, and use materials that don’t degrade if they do end up getting wet.”

Paul adds that – like many things in building in constructions – it all starts with good foundations. “The basement or the sub-floor area are the engine room of the house. And if you don't get the drainage and ventilation right in those sections of the property, that stale damp air is going to get pushed through the building, negatively affecting habitability and creating health issues for the occupants.”

So what are some of the most crucial things architects and designers should be paying attention to – or trying to address and fix? Drainage is the first thing Paul looks at. “When I get a set of plans from an architect and they want me to review waterproofing, the first thing I do is look at the hydraulic design,” Paul explains. “Because if you can get the water away from the surface and it doesn't build up on the back of the basement wall because there's good vertical drainage, then the element of risk of water coming through any failure in the membrane is significantly reduced.”

Paul adds that when it comes to bathroom design, the architects need to specify more than a 3740 minimum standard. “Architects need to indicate the areas that need to be waterproof, and the areas that need to be water resistant.” He explains that mostly that’s left up to the builder, but would be better specified by the architect.

“The next thing that's really important is substrate step down. I think the minimum step down should be 20 millimetres,” Paul adds. “I know that's difficult in multi-residential developments because of ceiling heights and other factors, but even 20 millimetres is better than no step down at all. There is now a mandatory requirement for the structural substrate of all wet areas to have fall. So in your design, you've got to allow for a minimum of one to 100 fall to the drainage outlet.”

Paul adds that it’s also really important not to have movement joints in bathrooms. “If you've got a multi-residential building, don't put a control joint in a shower recess or in a bathroom. Movement is one of the biggest things that can affect the membrane.”

And for balconies? Apart from dealing with the problematic planters, Paul prefers a balcony to have a concrete hob around the perimeter. “It reduces risk so that if you have a failure of the membrane there's a good chance that the concrete will contain the moisture and it won't leak out,” Paul says. “Always assume the worst and hope for the best,” he adds.

There is obviously much more to the subject of waterproofing so listen to the full episode and find out more about why drainage is paramount to maintaining the weather proofing of a building and why Paul doesn’t think adhering to the waterproofing standards is a guarantee of successful design.