Designing structures around trees

Designing structures around trees

When constructing near trees, it is important to consider the potential impact that the construction may have on the trees. In this article, we will explore how architects can design structures around tree roots, ensuring less than 10% total TPZ area encroachment while following the Australian Standard AS4970-2009, Protection of Trees on Development Sites.

Why Protecting Trees is Important

Trees are often an integral part of a property’s natural assets and are valued by the community or the tree owner. They are important for the environment, as they provide numerous benefits such as reducing the heat island effect and improving air quality. Therefore, it is essential to protect them during the construction process. By requiring tree reports and impact assessments as part of the planning permit process, councils can ensure that the trees are protected, and their value is preserved.

Understanding the Australian Standard AS4970-2009

The Australian Standard AS4970-2009, Protection of Trees on Development Sites, is a guide that provides guidance on the protection of trees on development sites. It is a useful resource for architects and developers who are planning to build near trees. The standard outlines various measures that must be taken to protect the trees, including assessing the trees’ health, identifying the tree protection zones (TPZs), and designing the construction project to avoid damaging the trees.

Understanding Tree Protection Zones (TPZs) and Structural Root Zones (SRZs)

Tree protection zones (TPZs) and structural root zones (SRZs) are two important concepts in tree protection during construction. The TPZ is an area around the tree encompassing canopy and rootzone where construction activities are restricted, while the SRZ is the area beneath the soil where the tree’s roots grow, limited to a smaller size. The size of the TPZ and SRZ depends on the size of the tree. These two radial measurements become larger for larger trees.

Assessing the Impact of Construction on Trees

Before designing any structure near trees, it is essential to assess the trees’ impact on the construction process. An impact assessment is an evaluation of the potential impact that a proposed construction project may have on trees on the property, the neighboring property, or council land. The assessment will identify any potential impacts on the trees and will recommend ways to minimize or mitigate these impacts. An arborist will conduct the assessment and provide a report detailing the findings. The arborist will assess the trees on the property to determine their size, species, age, health, and structure, among other factors. They will also assess the location of the trees in relation to the proposed construction and any other structures on the property. The arborist will identify any potential risks to the trees and recommend ways to mitigate these risks.

Designing Structures Around Tree Roots

When designing structures around tree roots, architects must ensure that the structure does not encroach on the tree’s TPZ. The TPZ is an area around the tree where construction activities are restricted. The size of the TPZ depends on the size of the tree, and it is calculated as a radial measurement from the center of the tree trunk. The TPZ can be calculated using the formula TPZ = DBH x 12, where DBH is the tree’s diameter measured usually at 1.4m from the gound. To ensure less than 10% total TPZ area encroachment, architects must design the structure in a way that avoids the TPZ or minimizes the TPZ’s impact. If the structure needs to be built within the TPZ, the architect must take measures to protect the tree roots. This can be achieved by using various techniques, such as root pruning, root barriers, or suspended slab construction.

  • Root pruning involves selectively removing tree roots to create space for the structure’s foundations. This should be done by a qualified arborist, who will determine which roots can be safely removed without damaging the tree’s stability or health.
  • Root barriers are physical barriers that are installed underground to prevent tree roots from growing into the construction area. This technique can be useful in areas where root pruning is not feasible.
  • Suspended slab construction is a technique used to build a structure above the ground without disturbing the tree roots. This involves building a platform supported by columns or posts that are installed outside the TPZ.

In conclusion, designing structures around tree roots is a complex process that requires careful planning and consideration of the tree’s health and well-being. Architects and developers must work closely with qualified arborists to ensure that the construction process does not harm the trees on the property. By following the Australian Standard AS4970-2009 and taking measures to protect the TPZ and SRZ, architects can ensure that trees on development sites are preserved and protected for future generations.

Facts about tree reports for development:
  • Tree reports are essential for protecting trees during the construction process.
  • The arborist’s report will provide recommendations for protecting the trees during construction.
  • Tree reports must be submitted as part of the planning permit process for many local councils.
  • The arborist’s report will identify any potential risks to the trees and recommend ways to mitigate these risks.
  • Tree reports are required to comply with the Australian Standard AS4970-2009, Protection of Trees on Development Sites.
Further reading:
  1. Australian Standard AS4970-2009:
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