Important Updates to AS4970–2025 Protection of Trees on Development Sites

On 30 May 2025, the Australian Standard for tree protection on development sites was updated (see AS4970-2025, Updated Standard) to supersede AS4970-2009 (former standard).

Critically, in the Updated Standard, the following changes have been made:

1. The new term ’Nominal Root Zone (NRZ)’ partially replaces the former terms ’Tree Protection Zone’ or ’TPZ', as regards roots and soils, reflecting the focus on root protection measures. The term ’TPZ’ should no longer be used to describe any root zone issues but is now only a reference to any above-ground tree protections.
2. Further, root investigations guidance is strengthened and includes preferred techniques, timing and documentation methods.
3. Soil and root zone management now includes detailed soil health maintenance recommendations, such as permeability aeration and moisture retention.

Importantly, the former standard’s TPZ Encroachment Guidance allowed for minor encroachments up to 10% with minimal justification.

In the Updated Standard, encroachment in the NRZ and TPZ is now provided for up to 20% (moderate encroachments) with provisions for 20-30% (major encroachments) using root mapping and tree sensitive designs.

Arborist, David Shrimpton from Koala Arbor, says that in his experience you could have up to 50% encroachment with strong arborist support for tree viability and with the right species.

Of interest to our clients will be the changes in the Updated Standard related to the monitoring and compliance of tree protection measures during construction, including reporting intervals.

Hat tip to David Shrimpton of Koala Arbor (david@koalaarbor.com) for letting us know of these changes. See the Standards Australia website for more information.