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Balcony failures - why do they leak?

September 17, 2019

Spring is here and this brings the rain, for many buildings with balconies it also highlights the failures of the waterproofing system causing leaking and major repair work being required.

Balconies are vulnerable to water seepage since they’re constantly exposed to the elements. The method of installation and the type of waterproofing 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, however unless some thought is given to the structure the waterproofing system is being applied to, the balconies location and orientation, covered or uncovered, it is more than likely  to have an impact on the effectiveness of waterproofing membranes.

The construction of each balcony is unique, and the risk of water intrusion is more likely if waterproofing systems don’t accommodate the balcony design. It is important to ensure that the balcony sub-floor framing is sound and solid and substrate material used is fit for purpose.

A waterproofing membrane 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.

Balconies also require proper drainage and correct isolation from the internal elements of a building, with the correct waterproofing system installed to prevent leaking.

Why do balconies leak?

The failure of the waterproofing system could be attributed to the fault of an inexperienced contractor, however 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 (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 (use of indoor membrane instead of outdoor membrane)

  • Minimal amount of drain outlets and the few that are installed are too small in diameter

  • Incorrect or insufficient fall to the drainage outlet

  • 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.

Many balconies are being constructed with minimal falls to the substrate, especially in multi-level apartments. A balcony with minimal fall is susceptible to water pooling and moisture between the membrane and tiles, known as “ponding”. If the waterproofing membrane applied cannot withstand ponding water, over time the membrane will break down, causing water leaks. Waterlogging can also cause joint failure, leading to leaks.

Other factors to consider

There are other contributing factors that can cause the waterproofing system to fail.

The type of tiles to be installed. Tile are subject to UV, dark coloured tiles soak up heat from the sun which will transmit the heat into the membrane and substrate causing movement to all the materials. Each material will move differently and could cause the membrane to tear. Once the membrane has torn penetration of any water can then seep under then membrane.

The installation of expansion joints to the tiles is very important to allow for the expansion and contraction of the tile. Lack of expansion joints can cause tiles lift due to compression and upheaving, thus tearing at the membrane allowing water migration into the room or apartment below.

Maintenance also play an important part of ensuring any water falling on the balcony flows to the 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.

Checking joints in the tiles to ensure they are still grouted and debris has not been ground into the join causing the membrane to be penetrated.

Australian Standards for Building Work (Waterproofing)

Waterproofing of external balconies must be carried out in accordance with Australian Standards that cover waterproofing membranes for external above-ground use. The relevant standards are:

  • Materials AS4654.1-2012

  • Design Installation AS 4654.2-2012

The builder needs to understand the methodology of how waterproofing is applied and how to prepare the substrate and prepare the building itself to receive the waterproofing. Builders and certainly water proofers do have to understand movement and the control of movement in buildings.

For further information, please call 1300 650 620 to speak with the HIA Building Services Team.