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 The Importance of Good Balcony Design

Now that the Spring rain is here, it’s a good time to focus on balcony design and how to avoid water damage. If the waterproofing system on a balcony is not installed correctly, it can result in major repair work being required.

Waterproofing methods and systems have changed considerably over the years.  They can be painted on, screeded on, rolled on, come in sheets and have mesh incorporated in them. Some thought needs to be given to the structure the waterproofing system is being applied to, the balcony’s location and orientation, and whether it’s covered or uncovered. These factors impact the effectiveness of the waterproofing.

The waterproofing is really only as good as the substrate that it’s sitting on. If you don’t have a good foundation and the building moves later on, it is very likely that the substrate will move, the linings will move and the waterproofing membranes will break.

Good design will minimise problems with balconies

In most cases the common contributing factors to failures of balconies can be attributed to:

  • Lack of planning prior to construction,
  • Incorrect substrate and use of substrate materials,
  • The substrate is not sound and solid and allows for too much movement,
  • The substrate in not cleaned and made ready to accept the membrane (dust, uneven surfaces, rough joins – membrane won’t adhere),
  • Incorrect membrane selection  – indoor used instead of outdoor membrane,
  • Minimal amount of drain outlets and some may be too small in diameter,
  • Incorrect or insufficient fall for drainage,
  • No overflow provisions provided,
  • Lack of detail around waste and other penetrations,
  • Inadequate flashing or waterproofing to the balcony floor and external wall join or to the treatment at the window door opening.

By ensuring that some thought has gone into the preparation and design of the balcony and the waterproofing system to be used can save time and expense in the future to rectify a leak.


Drainage is a key element and if the waterproofing membrane applied cannot withstand ponding water, over time the membrane will break down, causing water leaks. Any water falling on the balcony also needs to flow to well-maintained drainage outlets.

Blocked floor wastes or outlet drains, can cause pooling or ponding of water which can enter the building via the openings or above any flashing level.

Australian Standards for Building Work (Waterproofing)

There are two Australian Standards applicable to the waterproofing of external balconies these are:

AS4654.1-2012 waterproofing membranes for external above-ground – Materials

AS 4654.2-2012 – waterproofing membranes for external above-ground -Design and Installation

HIA members can contact our technical team for more information.

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