Key Considerations for Waterproofing Rooftop Gardens

Key Considerations for Waterproofing Rooftop Gardens


Beautiful rooftop garden

At Danrae Group, we provide high-quality, compliant and comprehensive waterproofing solutions across commercial, civil, construction, government and strata sectors.

As experts in end-to-end waterproofing solutions, we know that effective waterproofing requires a holistic approach. This means that we may waterproof several areas of a property, including basements, lift shafts, balconies – and rooftop gardens.

Also called green roofs, rooftop gardens are becoming increasingly popular in strata and commercial spaces due to their environmental, aesthetic and wellbeing benefits. They do require a slightly different approach to standard flat roof waterproofing, with a few key considerations.

Rooftop park in the city

About rooftop gardens


Green roofs can be created on pitched or flat roofs, with the surface partially or wholly filled with soil and vegetation that grows above a waterproofing membrane.

A green roof consists of several layers. Vegetation sits above a substrate layer, which contains drainage and landscaping materials. And beneath this is the protective waterproofing membrane. The membrane acts as a barrier to water seepage from both environment and garden.

The Australian Government’s Your Home guide to sustainable homes lists several benefits of green roofs, including improved sound, heat and cooling insulation, increased biodiversity, reduced and slowed stormwater runoff, capture of pollutants and interestingly, a longer roof lifespan.

Glass building house covered by green ivy

Types of green roofs


While the definitions are not rigid, green roofs are usually classified as intensive or extensive. Typically, extensive green roofs are shallower gardens, with less than 200mm of soil and ground cover vegetation. This type can be retrofitted to existing buildings, be low maintenance and relatively economical, but as they support weights of between 60–200kg/m2 only, they are not suitable for people to access.

Intensive gardens can hold soil up to 1m deep and support vegetation up to tree size and a wide variety of plantings.

Intensive gardens support much greater loads – between 180–500kg/m2 or more – so they are suitable for access.

Intensive green roofs are obviously more expensive given structural requirements, but they also have much greater thermal and acoustic properties. Intensive rooftop gardens generally include additional features such as seating, paved areas and decking.

Aerial view of roftop garden

Membrane considerations for green roofs


The Danrae Group team is certified and experienced to work with all membrane varieties, so we understand best options for diverse applications.

Rooftop gardens require a membrane that will support the garden weight, be robust enough to resist gardening chemicals, be able to withstand diverse weather conditions and damp soil, and be flexible to respond to structural movement.

Given vegetation roots can cause significant damage to unsuitable membranes, it’s important that the membrane also be root-resistant. In a recent blog on new waterproofing technology, we featured Ardex Root Repell™, a great product that has a plant root repellent impregnated within the membrane. It works to repel roots away from the membrane without killing them, so it’s a good option for both rooftop gardens and planter boxes.

Danrae Group

Managing your rooftop garden waterproofing


At Danrae Group, our comprehensive waterproofing solutions include diagnostic, solution design, remediation, waterproofing and preventative maintenance. And we can onboard for new construction or existing rooftop gardens.

If you have a leak in a rooftop garden, we use a variety of testing techniques and technology to pinpoint the exact location. With diverse trades skills in-house including building, carpentry and tiling, we look after every stage of roof remediation, including site preparation and induction, rebuild and clean up.

And our full project management covers every aspect of a project including crane hire, council permits and tenant communication.

The Danrae Group team has the expertise to provide a complete waterproofing solution for your rooftop garden. Contact us to find out more.

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