Table of Contents
Deep Planting Zones
What is Deep Planting?
A deep planting zone is an ‘in-ground’ area of a specific width and breadth that is dedicated to landscape and is able to sustain large subtropical shade trees.
The aim is to retain or provide significant vegetation to urban areas for shade, amenity, offset of carbon emissions and to mitigate the heat-island effect in urban areas caused by dense built-form and hard surfaces that fill cities.
Due to the intensification of our cities with additional built form, (concrete, walls, pavements, buildings and the like) providing sufficient deep planting areas ensures we are retaining and providing dedicated landscape spaces within the our cities.
Brisbane City Council has specific requirements for deep planting however it does depend on the relevant code.
Dual Occupancy Code – Deep Planting Requirements
The Dual Occupancy Code is not as strict when it comes to deep planting as the Multiple Dwelling Code.
Generally it is explained as:
- provide an opportunity for the co-location of deep planting areas to support the retention of significant vegetation and establish large subtropical shade trees within the street or on adjoining premises.
Multiple Dwelling Code – Deep Planting Requirements
The Multiple Dwelling Code is much stricter and has specific requirements which are non-negotiable.
It includes:
- The deep planting areas must be 100% open to the sky (no overhead roofs)
- No driveways, maneuvering or hardstand areas and pedestrian paths
- No underground development (basements, tanks) or infrastructure (services)
- In natural ground (not in cut/fill area or a planter)
- Can incorporate existing trees
- Some times must meet a minimum dimension (width and breadth).
Clearly, not all of the landscape area typically indicated on a site plan meets these requirements.
Multi-storey apartment buildings often include garden areas at entry areas that are located beneath upper levels. Multiple services and structural footings are often located beneath landscape zones.
4 Common Intrusions to Deep Planting Zones
Services
(transformers, fire boosters, water meters, switchboards)
A common and significant (size) intrusion to a deep planting zone is the introduction of a pad-mount transformer. Ironically, the requirements for locating transformers are quite similar to deep planting zones so of course this is exactly where they end up.
Understandably, the requirement for these is often not certain until after a DA is achieved. Because of this, it is now common for Brisbane City Council to require transformers to be indicated on site plans for development approval.
Stormwater infrastructure
(overland flow zones, stormwater pipes, bio-basins)
Overland flow zones are often accompanied by restrictions to the density and type of vegetation that can be planted within it.
Sometimes it means no planting at all. Where a stormwater pipe is shallow, any large tree planting will pose a risk to the integrity of the pipe. Many tight development sites make use of underground stormwater treatment devices.
But when the need to an open bio-retention area is identified late in the design process, often the only location left on the site to put these are landscape areas.
At times a bio-retention area may be designed to accommodate trees, but this falls short again, as the very design of a bio-zone involves replacing the filter media at a future time, thereby removing any vegetation.
Footings
Footings to walls and structures can significantly impact landscape areas in terms of the amount of growing media that is available to plants. Boundary walls that require footings to be contained within the site can result in significant footing extents that commonly impact landscape areas.
For instance, a typical landscape buffer zone might be 2 metres wide, which normally allows small columnar trees and screen shrubs to be planted.
If such a buffer happens to be located adjacent to a wall that has a footing intruding 800mm into the landscape area, it could mean that no trees can be planted in that zone unless footings are greatly lowered, adding significant cost to the whole exercise.
Access
(footpaths, hardstand, parking spaces, driveways)
Fire exits and access paths to service areas are items that are at times resolved quite late in a project. Where landscape areas are minimal, these can have a big visual impact on the resulting amount of planting area, as well as affecting what areas can be counted as deep planting.
The challenge here is that many of these components remain in a conceptual form throughout the DA phase. Often their resolution occurs after key structural components of buildings and structure and it is then simply too late.
While each may be small individually, their combined impact on the amount of deep planting can be significant to the point where landscape conditions cannot be fulfilled.
The key is to factor in realistic area estimates required for all components and services at the early stages. Getting a Landscape Architect involved early in the site planning phase allows an opportunity for feedback that can lead to a more robust proposal that will withstand inevitable change.
What do I need to be aware of?
Preliminary Calculations Could Mean the Difference to ‘Approved’ or ‘Not Approved’
An area designated as deep planting should be treated as a planted garden bed area that includes trees. Turf is not considered an acceptable solution.
It is important that a client/developer understands the specifics of the deep planting requirements under the Landscape Code and also under the specific code their property falls under.
Deep planting requirements can make a significant difference to the size of a proposed dwelling or building on a specific parcel of land. On narrow and particularly small lots, this could make the difference to the amount of negotiation required to achieve Development Approval or even in the more extreme whether a project is worth pursuing or not.
It is important to seek professional advice prior to spending a huge amount of fees on consultants and then end up finding out down the track that there is insufficient space on a parcel of land.
How Much Deep Planting do I need on My Site?
This will depend on your local jurisdiction, the specific city plan and the local authority requirements. Brisbane City Council have specific requirements depending on the zone that applies to your particular parcel of land.
It is best to engage a Town Planner to determine what is required for your property. At time of writing, Brisbane City Council requires a deep planting area of 10% of the property. However there are several other factors involved and it is best to engage a Town planner and landscape architect to determine the specific requirements for your development.
What are the Benefits of Deep Planting to a city?
Deep planting brings significant benefits to our cities and town. The following are just some of the advantages of deep planting.
Improved air quality
Trees play a crucial role in purifying the air by absorbing carbon dioxide and releasing oxygen through photosynthesis. Deep planting increases the number of trees in urban areas, leading to better air quality and reduced pollution levels. This is particularly important in cities where air pollution is a significant concern.
Urban heat island mitigation
Urban areas tend to have higher temperatures compared to surrounding rural areas due to the urban heat island effect. Deep planting helps mitigate this effect by providing shade and evaporative cooling. Trees create a cooling effect through evapotranspiration, reducing energy demand for air conditioning and enhancing overall comfort in cities.
Stormwater management
Urban areas often face challenges related to stormwater runoff, which can lead to flooding and increased strain on drainage systems. Deep planting helps manage stormwater by absorbing and retaining rainwater through the tree’s root systems. This reduces the burden on stormwater infrastructure and improves water quality by filtering pollutants before they enter water bodies.
Biodiversity and habitat creation
Urban areas are typically characterized by a loss of natural habitats. Deep planting helps restore biodiversity by creating new habitats for birds, insects, and other wildlife. Trees provide food, shelter, and nesting sites, promoting urban wildlife diversity and supporting ecological balance in cities.
Aesthetics and well-being
Trees contribute to the visual appeal of cities, softening the built environment and adding natural beauty to urban landscapes. Research has shown that exposure to green spaces and trees can have positive effects on mental health, reducing stress levels and improving overall well-being. Deep planting enhances the aesthetic value of cities and creates more inviting public spaces for residents and visitors.
Noise reduction
Trees can act as natural sound barriers, absorbing and deflecting noise from traffic and other urban sources. Deep planting along busy roads and in densely populated areas can help reduce noise pollution, creating a more peaceful urban environment.
