Tree protection zones: what Melbourne builders need to know

What NRZ, TPZ and SRZ mean under AS 4970:2025

AS 4970:2025 (Protection of trees on development sites) is the current Australian Standard. Standards Australia lists it as published in 2025 and superseding AS 4970-2009 (Standards Australia catalogue). Melbourne councils refer to it in their tree protection guidance and use three zone terms. The descriptions below come from published council guidance, not from the standard itself, which was not reviewed for this guide:

• Notional Root Zone (NRZ) is a calculated zone based on trunk measurements. Council Arboriculture Victoria's free AS 4970:2025 calculator works out diameter at standard height (DSH) and the NRZ and SRZ from a trunk circumference or diameter (Council Arboriculture Victoria). Nillumbik Shire Council asks arborist reports to state the NRZ, SRZ and TPZ dimension for every tree (Nillumbik Shire Council). The NRZ is a starting point for assessing where roots may be, not a precise map of the root system.
• Tree Protection Zone (TPZ) is the area protected on site during construction. The City of Boroondara describes it as an area above and below ground that is protected with fencing, mulch and ground protection throughout construction (City of Boroondara). Hobsons Bay City Council describes the TPZ as a zone above and below ground at set offsets from the trunk, calculated by multiplying the trunk DSH (measured at 1.4 metres above grade) by 12, and says it must be isolated from all construction activities (Hobsons Bay City Council). Council pages differ on whether they call the calculated zone the NRZ or the TPZ, so follow the terms and dimensions used in your arborist report and permit.
• Structural Root Zone (SRZ) is the second calculated zone produced by the AS 4970:2025 calculator and listed in Nillumbik's report requirements. Have the project arborist explain what any works near the SRZ mean for the tree's stability and retention before excavation or design changes.

Do not treat a zone calculation as permission to encroach. Confirm proposed access, excavation and fencing changes with the project arborist and the relevant council before work.

Initial calculation vs. site-specific protection plan

A zone calculation gives a starting point for understanding how much area a tree's root system may need. Translating it into the protection zone that is fenced on site is the project arborist's job, and involves assessing the actual site layout, soil conditions and what the design proposes within or near the calculated zones.

Hobsons Bay City Council's development guidance describes two protection documents, which it says were formerly known together as a Tree Protection Management Plan (TPMP):

• A Tree Protection Plan (TPP) is the visual document: a site plan showing the location of retained trees, their TPZs and the location of protection devices such as fencing.
• A Tree Protection Specification (TPS) is the written document: the protection measures and management processes to be implemented and followed throughout development or construction works.

Hobsons Bay says these documents must be provided to all workers on site, with a copy always available, and that failing to comply with them may breach the planning permit and incur penalties. Check which documents your own planning permit or council requires. For more about this documentation, see the Tree Protection Specification and Plan service.

Before you finalise the design

The earlier you account for retained trees, the fewer problems during construction. Check these before committing to a design:

1. Identify which trees must stay. Check the planning permit, overlays, council local laws and any vegetation controls that apply to the property. Trees on neighbouring properties and council land may also need protection if their root zones extend into your site.
2. Engage an arborist before finalising plans. A tree impact assessment examines how the proposed design affects retained trees and identifies where the proposed works come close to or inside the protection zones. This step can save redesign costs later.
3. Check access, services and storage. Plan vehicle and machinery access routes that avoid root zones. Ask the arborist whether underground services (water, drainage, power, gas) can be routed outside the protection zones and, if not, what installation method they will specify. Identify where materials, equipment and site sheds can be stored outside the TPZ.
4. Account for neighbouring trees. A retained tree on the neighbouring property may have roots extending well into your site. If a neighbour's tree has a protection zone that overlaps your proposed works, include it in the arborist assessment and the protection plan.

Not sure whether you need an arborist report at this stage? Start with the guide to when an arborist report is needed.

Before excavation or site work begins

Once the design is approved and you are ready to start on site, these steps protect the trees and your permit compliance:

1. Install TPZ fencing before any site activity. Fencing must be in place before demolition, excavation or material delivery. Your planning permit will specify the fencing requirements; check it for minimum height, signage wording and placement.
2. Keep materials and equipment outside the TPZ. No fuel, chemicals, building waste, soil, machinery or temporary structures inside the fenced area. Plan your site layout so deliveries and storage have a designated area away from retained trees.
3. Avoid soil disturbance within the TPZ. No excavation, grade changes or open-cut trenching for services within the protected area unless your permit and the endorsed protection documents specifically allow it, using the method the project arborist specifies.
4. Brief every trade. Subcontractors, delivery drivers and machinery operators all need to know where the TPZ boundaries are and what is not permitted inside them. A printed copy of the TPP on the site noticeboard helps.
5. Do not attach anything to retained trees. No wires, nails, screws, signs, lights or temporary fixings.

Breaching TPZ conditions can trigger enforcement action from council. Nillumbik Shire Council notes that penalties apply for each tree affected (Nillumbik Shire Council). Boroondara warns that damage to a protected tree during construction could result in fines or prosecution (City of Boroondara). Check the enforcement provisions that apply to your council area.

What councils typically require

Tree protection conditions appear on planning permits across Melbourne, but the detail varies between councils. Three examples:

• Hobsons Bay City Council says it is important to engage a suitably qualified arborist (minimum AQF Level V or equivalent) before any plans are drawn up, describes TPZs assigned in accordance with AS 4970:2025, and says the TPZ must be isolated from all construction activities. Its guidance also describes the TPS and TPP documents outlined above (Hobsons Bay City Council).
• Nillumbik Shire Council requires TPZ fencing at a minimum height of 1.5 metres with "Tree Protection Zone – No Entry" signage on each side before any site work or demolition begins. Their planning permits list prohibited activities including material storage, soil disturbance and open-cut trenching for services (Nillumbik Shire Council).
• City of Boroondara says the TPZ is usually protected with fencing, mulch and ground protection, and that works within the TPZ of a significant tree need a Tree Removal/Works Permit. It lists machine excavation, parking vehicles and machinery, compacting soil or changing levels, and installing utilities and signs as activities that can damage trees and may require council approval or an arborist's supervision. Preparing chemicals (including cement products), storing or dumping materials or waste, washing down and refuelling equipment, and lighting fires are not permitted within the TPZ (City of Boroondara).

Other Melbourne councils apply similar conditions, but definitions of protected trees and local law requirements differ. Always check the specific planning permit and council guidance that applies to your site before starting work.

Common questions about tree protection zones

Get tree protection advice for your project

If you are planning construction near retained trees and need to understand the protection requirements, Arbor Analytics can help. We prepare tree impact assessments, tree protection specifications and plans and provide arborist reports for Melbourne builders working through council requirements.

What this guide does not cover

This guide is general information for people building near retained trees in Melbourne. It does not cover the tree protection rules of every council, tree works on council land or road reserves, or what a specific tree can tolerate. Zone dimensions, fencing requirements and any approved works inside a zone come from the arborist report, protection documents and permit conditions for your site, not from this page.

Sources

• Hobsons Bay City Council: Protecting trees during development (accessed 29 September 2026)
• Nillumbik Shire Council: Tree protection zones (accessed 29 September 2026)
• Nillumbik Shire Council: Arborist report for planning applications (accessed 29 September 2026)
• City of Boroondara: Protect trees during construction (accessed 29 September 2026)
• Council Arboriculture Victoria: Resources and AS 4970-2025 calculator (accessed 29 September 2026)
• Standards Australia catalogue: AS 4970:2025Protection of trees on development sites, listed as current, published 2025, superseding AS 4970-2009 (accessed 29 September 2026). The full standard was not reviewed for this guide; zone descriptions above are taken from the council guidance listed here.