Building Blox: Episode 1 - Why Balconies Leak

Building Blox is an educational video series produced by Ross Taylor & Associates, featuring the voice of Ross Taylor.

More training materials and resources: https://www.rtas.com.au/waterproofing...

Following is a transcript of Episode 1: Why Balconies Leak

Modern high-rise apartment construction is often plagued by a wide variety of building defects. Amongst managers, owners and builders water penetration problems are known to be the most frequent and most expensive type of defect. Over recent years, leaks in and around balconies have become the No 1 source of water penetration problem in modern unit construction.

Drive down the major highways of your city and the white staining and leaking of balconies is evident. Not only is this unsightly but in many cases balconies leak internally causing damage to surfaces and inconvenience to occupants.

This module will deal with these types of leaks.

Balcony leaks reveal themselves in various forms: Leaking into interior spaces via doors, windows and flashings. Leaks through cracks in balcony soffits or ceilings, which form stains, drips and stalactites. Leaching up through tile surfaces causing unsightly white stains.

Or leaching through balcony edges. To find out why these occur we need to go right back to the beginning of the building process.

Let's follow one scenario and how it leads to defects of this type.

Step 1: a developer decides to build a set of apartments and an architect is asked to put together initial drawings. Ideally at this time, balconies would be designed with integral hobs, integral falls and step-downs at sliding doors. This design lets most of the water shed from the balcony without running internally or leaching to the outside.

However, in this case and many others this isn't what happens. The developer needs to maximize the number of floors to make his profit on the job. So, the architect will be asked to reduce the floor to ceiling heights. This means step-downs at the sliding doors and integral falls in the structural slab are eliminated.

The builder is selected via a cheapest price tender, which means he'll need to pick the cheapest subcontractors to win the job. Part of the deal is for the builder to take over finishing the design detailing of the building.

Once he reviews the drawings he realizes that he can make a saving by pouring the concrete slab without an integral hob at the perimeter. This gets back some of the profit given away at tender stage.

We now have a flat plate slab design for all the balconies. All the protections to water penetration from our original sketch have now been removed. And somehow they need to be added back. Without a step down in the slab the doorframe is bolted straight to the flat concrete surface. To keep the balcony tile and tile bed in place aluminum angle is attached at the edge of the slab. Without an integral fall in the slab the waterproofing membrane is applied straight to the concrete, angles and frame.

To get the falls in the surface of the balcony to shed the water cement topping screed and tile is then added.
The building is handed over to the new owners. The leaking and leaching begins. Lets see how this unfolds:

Once the step down at the sliding doors is deleted, the build up of the tiles and tile bed makes the water level on the outside of the sliding door higher than inside.

Since the membrane was only turned up to the underside of the frame, it is easily overflowed in bad storms. Then 'bingo' - water entry and wet carpet. Once the integral fall in the concrete slab is taken away the membrane has to be applied to a flat plate and stores water forever more.

There is huge differential movement between each of these elements as they respond to thermal changes, flexing from wind pressure and settlement of the structure. Remember a single continuous structural concrete profile would not be subjected to many of these differential stresses.

The builder has only allocated enough money for a thin acrylic type membrane to be applied. This type of membrane cannot bridge the huge movements that take place between the different bits that have been added to the flat plate slab. Any thin or rigid membrane is likely to crack at this point. Then the stored water has time to seep through the concrete dissolving calcium and other minerals as it runs down the cracks. On exposure to the air the mineral solution dries, leaving behind stalactites, just like in caves...