What the New AS 4970:2025 Tree Protection Standard Means for Your Development Project

If you’re planning a development project in Melbourne, whether it’s a new build, renovation or subdivision, it’s essential to understand AS 4970:2025, the newly updated national standard for tree protection on development sites.

Introduced in 2025 to replace the older AS 4970:2009, this standard brings significant changes to how trees are assessed, protected and retained during construction. These updates affect developers, builders, architects, planners and homeowners alike and can directly influence the speed, approval and success of any project that involves trees.

Here’s a quick summary of the major updates:

Key Area	AS 4970:2009	AS 4970:2025
Base Metric	DBH × 12 = TPZ	NRZ = DSH × 12 then TPZ derived
Encroachment Response	Distance-based, qualitative	% of NRZ impacted triggers Minor, Moderate or Major
Root Zone Protection	TPZ only	NRZ and SRZ used together to define protection zones
Tree Reporting	Single AIA report	Staged: PAR, AIA, TPS and TPP
Arborist Involvement	After design phase	From site acquisition through to completion

Understanding these changes helps reduce redesign risk, avoid compliance issues and improve long-term tree health around development sites

What Is AS 4970:2025?

AS 4970:2025 is the newly revised Australian Standard for protecting trees on development sites. It replaces the older 2009 version and provides a more structured and enforceable approach to managing trees in and around construction zones. Whether you’re a builder, developer, planner or homeowner in Melbourne, understanding this new standard is essential if your project involves trees on-site or nearby.

A National Framework for Tree Protection

AS 4970:2025 sets out clear guidelines for assessing, retaining and protecting trees during all stages of property development. Unlike the older version, which was often used as a reference guide, the 2025 update has become a more central, enforceable part of planning regulations across Australia. Councils, planning authorities and arborists now use this framework to determine whether a development can proceed without harming existing vegetation.

Who Needs to Comply?

Anyone planning to build, renovate, subdivide or excavate land where trees are present will need to comply with AS 4970:2025. This includes property developers, builders, architects, landscape designers and homeowners. Local councils are increasingly conditioning planning permits based on this standard, which means non-compliance can lead to project delays, fines or the loss of valuable trees.

Why the Update Was Necessary

Urban development in cities like Melbourne has placed increasing pressure on mature trees. The 2009 standard was often applied inconsistently, and it didn’t fully address modern construction methods or tree science. AS 4970:2025 fills these gaps by introducing a staged planning process, quantifiable encroachment thresholds and a greater role for project arborists in early design decisions.

Key Changes in AS 4970:2025 (vs. AS 4970:2009)

Feature	AS 4970:2009	AS 4970:2025	Why It Matters
Base Metric	TPZ = DBH × 12	NRZ = DSH × 12 (then TPZ derived from NRZ)	Provides a more accurate reflection of usable root zone area
Encroachment Assessment	Based on distance or judgement	Measured as % of NRZ area affected	Introduces clear thresholds: Minor, Moderate, Major
Encroachment Response	Qualitative	Requires staged response based on % NRZ and SRZ involvement	More objective and enforceable; earlier arborist intervention
Structural Root Zone (SRZ)	Defined but not heavily enforced	SRZ breach automatically treated as Major encroachment	Prioritises protection of critical structural roots
Tree Viability Offsets	Rarely used	Explicitly encouraged if NRZ is lost	Allows for design flexibility without sacrificing tree health
Crown Protection	Minimal guidance	Dedicated section with clear instructions	Equal focus on canopy and root zone protection
Planning Integration	Arborist engaged late	Arborist involved from site acquisition to post-completion	Prevents redesign and ensures continuous compliance
Tree Reporting	Single-stage report (AIA)	Staged: PAR → AIA → TPS and TPP	Matches the pace of project development and reduces confusion
Document Structure	Lightly defined	Clearly sequenced to project phases	Improves coordination between arborists, planners and contractors
Construction Compliance	Assumed	Requires monitoring, certification and post-completion check	Stronger protection, accountability and documentation throughout construction

The 2025 update to the Australian Standard introduces several important changes that affect how trees are protected during development. These updates are designed to reduce tree loss, improve compliance, and bring arborists into the project much earlier. Here’s a breakdown of what’s new and why it matters.

1. New Root Zone Metric: NRZ Replaces TPZ as the Starting Point

In the 2009 standard, the Tree Protection Zone (TPZ) was calculated directly from the trunk diameter (DBH × 12). In AS 4970:2025, the Nominal Rootable Zone (NRZ) becomes the base metric instead. It’s calculated using the tree’s Diameter at Standard Height (DSH × 12). The TPZ is then derived from this NRZ.

This shift gives a more accurate picture of the underground root spread and soil volume a tree needs to survive. It results in better planning around tree roots and reduces the likelihood of accidental root damage during site works.

2. Encroachment Is Now Measured in Percentages

Rather than relying on vague distance measurements, AS 4970:2025 introduces a clear system based on the percentage of NRZ affected. It defines three encroachment levels:

• Minor: ≤10% of NRZ
• Moderate: 10–20% of NRZ
• Major: >20% of NRZ or any encroachment into the SRZ

Each level has its own required response, from basic protection measures to full arborist-led design reviews. This ensures decisions are more objective and defensible, especially in council or legal disputes.

3. Structural Root Zone (SRZ) Becomes a Hard Limit

The Structural Root Zone (SRZ) was already defined in AS 4970:2009, but in the 2025 version, any encroachment into the SRZ is automatically classed as a major impact. The SRZ is where the tree’s most critical roots are located, so disturbing this zone can seriously compromise stability and health.

This change reinforces the need for early design interventions. Builders and developers must plan around the SRZ from the start, rather than hoping to negotiate later.

4. Tree Viability Offsets Are Now Explicitly Allowed

If a section of the NRZ is disturbed, the new standard encourages compensating by protecting an equivalent area elsewhere within the TPZ. This gives developers more flexibility in tight sites while still preserving enough soil volume and root access for tree survival.

For example, if a corner of the NRZ is lost to footings or drainage, an offset can be created by extending fencing or root protection elsewhere. This approach allows for practical design solutions without compromising the tree.

5. Arborists Now Have a Bigger Role, Sooner

In AS 4970:2009, arborists often came in after the design was already finalised AS 4970:2025 changes that by embedding the arborist into every stage of the development, from site acquisition through to post-construction certification.

This early involvement helps reduce redesign costs, identify high-value trees before site layout is locked, and improve communication between planners, designers and contractors.

The New Encroachment Decision Ladder

One of the most practical and impactful updates in AS 4970:2025 is the introduction of a three-tiered encroachment system. This new framework gives developers and arborists a clear, consistent way to assess how much a proposed structure or excavation will impact a tree’s root system, and what level of response is required.

Instead of relying on distance alone, encroachment is now measured as a percentage of the Nominal Rootable Zone (NRZ) affected by development. This allows for more precise and informed decisions, particularly on complex or space-constrained sites.

1. Minor Encroachment (≤10% of NRZ, Outside SRZ)

Minor encroachments are considered low risk if they remain outside the Structural Root Zone (SRZ). These situations usually do not require changes to the design, but protective measures must still be active on-site. This may include temporary fencing, ground protection and offsetting any lost root area within the Tree Protection Zone (TPZ).

Provided the tree has not suffered recent or repeated disturbances, this level of impact can typically be managed without long-term damage to tree health.

2. Moderate Encroachment (10 to 20% of NRZ, Outside SRZ)

Moderate encroachments are the official trigger for involving a project arborist early in the planning phase. The arborist will review the design and may suggest root investigations, ground-penetrating radar (GPR), or soil analysis to evaluate how the tree might respond to the proposed works.

At this stage, the design may need adjustments to avoid additional stress. Service routes, construction zones and excavation methods should all be reassessed to minimise long-term impacts on tree stability and health.

3. Major Encroachment (More than 20% of NRZ or Any Encroachment into SRZ)

Major encroachments carry a high level of risk and require strong evidence to justify proceeding. If over 20 per cent of the NRZ is affected, or if any activity occurs within the SRZ, the developer must demonstrate that the tree will remain viable with mitigation.

This typically involves advanced arboricultural assessments, including root mapping, soil testing, a review of site history, and examples from other projects. If viability cannot be confidently proven, the tree may need to be removed or the design revised significantly.

This structured system gives all parties a clearer path for making informed decisions about tree protection. It replaces vague judgment calls with measurable thresholds, which helps avoid disputes and ensures better long-term outcomes for trees and developments alike.

Planning Workflow: What Developers Must Now Do

AS 4970:2025 outlines a structured planning process that integrates tree protection into every stage of development. This approach shifts tree care from being an afterthought to becoming a core part of project design and approval. Developers, builders and architects must now engage with arborists earlier and ensure tree-related planning aligns with the updated standard.

1. Site Acquisition

Tree protection begins well before construction starts. During site acquisition, developers must identify any legal or planning constraints related to trees, including overlays, heritage listings or significant landscape features. Understanding tree risks and obligations at this early stage allows better feasibility planning and reduces approval delays.

2. Survey and Preliminary Arborist Report (PAR)

A qualified arborist must carry out a detailed tree survey using accurate site data. The Preliminary Arboricultural Report (PAR) assigns Nominal Rootable Zones (NRZs) to trees, assesses their health and structural condition, and determines whether they should be retained, relocated or removed. This report becomes the foundation for the tree protection overlay in the early design phase.

3. Preliminary Design with NRZ Overlay

Designers must overlay the NRZs on architectural and engineering drawings during the concept stage. The goal is to reduce or eliminate disturbance within these zones by adjusting building footprints, driveways, drainage and service alignments. Early coordination at this step can prevent the need for major redesigns later.

4. Arboricultural Impact Assessment (AIA)

If any works are proposed within an NRZ, an Arboricultural Impact Assessment (AIA) is required. This report analyses the type and severity of encroachment, outlines design alternatives considered, and provides mitigation strategies where applicable. It also justifies any necessary tree removals and evaluates tree viability based on the latest encroachment thresholds.

5. Tree Protection Specification (TPS) and Tree Protection Plan (TPP)

These two documents provide detailed instructions for how trees will be protected during construction. The TPS sets out protection requirements such as fencing, signage, and construction restrictions, while the TPP maps this information onto the site plan in a staged, sequenced format. Both are living documents that should be updated throughout the project.

6. Pre-Site and Construction Phase Actions

Before site works begin, all protective measures must be installed and certified by the project arborist. This includes setting up fencing, verifying tree retention or removal, and ensuring the protection zones are clearly marked and respected. During construction, the arborist may need to supervise pruning, monitor root zones and provide updated certifications for council compliance.

7. Completion and Post-Development Care

Once the build is complete, the project arborist must certify the final condition of retained trees. All temporary protection measures are removed, and if required, a post-development maintenance plan is implemented to support long-term tree health. This final sign-off is often essential for planning approval and occupancy certification.

This staged approach promotes better project coordination, fewer delays and a higher success rate for tree retention. It also ensures compliance with councils and planning authorities who are increasingly referencing AS 4970:2025 in development conditions.

Why Early Arborist Involvement Matters

One of the most important shifts in AS 4970:2025 is the increased expectation for early and ongoing involvement from a qualified arborist. Tree protection is no longer a one-off report completed just before permit submission. It is now a strategic component of the development process, starting from the moment a site is assessed for feasibility.

1. Arborists Help Identify Tree Constraints Before Design Lock-in

Engaging a project arborist during the early planning stage ensures that tree-related risks and opportunities are properly understood. Trees that appear healthy may still pose underground challenges, while others may be in decline and suitable for removal. Early identification of protected trees, significant root zones and SRZs allows architects to design around these constraints without needing to rework approved plans later.

2. Reduces Risk of Redesign, Delays and Compliance Issues

When arborists are involved after plans are submitted or approved, there’s little room left to make meaningful changes. This often leads to costly redesigns, delays in permit approval or even breaches of tree protection requirements during construction. Early arborist input reduces these risks by shaping the design to comply with AS 4970:2025 from the start, streamlining the approval process.

3. Enables Smarter, More Flexible Construction Planning

An experienced arborist can recommend practical ways to retain valuable trees while still meeting development objectives. This includes using root mapping, air spading, or creating offset zones within the TPZ to balance structural needs with ecological protection. Arborists also work closely with engineers and contractors to ensure construction methods are tree-sensitive, such as using pier-and-beam footings instead of slabs or adjusting excavation methods.

Early arborist involvement is not just about ticking a compliance box. It adds real value to the design and construction process by minimising risk, improving outcomes and enhancing the long-term health of trees in urban environments. At TLC Trees, we work closely with clients from day one to ensure their project meets the latest tree protection standards with confidence.

Real-World Impacts: What This Means for Your Build

AS 4970:2025 is not just a technical update. It has real implications for how you plan, design and execute construction projects when trees are involved. From increased documentation to stricter compliance enforcement, developers and builders must now take a more strategic and proactive approach to tree protection.

1. Poor Planning Can Lead to Costly Redesigns

If tree protection requirements are not factored in from the beginning, your project may face major delays once the council reviews the arborist report. Design changes made late in the process are expensive and time-consuming, especially if construction has already started. By understanding the encroachment limits and planning with NRZ and SRZ boundaries in mind, you can avoid setbacks and keep your timeline on track.

2. Non-Compliance May Trigger Legal and Financial Risks

AS 4970:2025 provides clear thresholds and documentation standards that councils will now use to enforce compliance. If your site activities damage a protected tree, whether above or below ground, you may face fines, stop-work orders or insurance complications. Proper fencing, certified protection measures and arborist supervision are no longer optional; they are critical to meeting your legal obligations.

3. Tree Protection Is Now a Selling Point, Not a Burden

Today’s homebuyers and local councils value green space and mature trees. By preserving healthy, established trees on-site, you can increase property value and community appeal. A well-executed Tree Protection Plan (TPP), backed by professional arborist reports, not only meets the standard—it signals quality, sustainability and foresight in your project.

Incorporating AS 4970:2025 into your development strategy helps avoid risks, enhances your approval success, and contributes to a more attractive and environmentally responsible end result.

At TLC Trees, we help you align every stage of your project with the new standard, so you can build with confidence.

How TLC Trees Can Help

At TLC Trees, we understand that the new AS 4970:2025 standard can seem complex and overwhelming, especially when you’re juggling permits, contractors and tight construction timelines. That’s why we offer expert arborist services tailored to help homeowners, developers, and builders navigate these changes with ease.

1. Arborist Reports That Meet Council Requirements

We prepare fully compliant arborist reports at every project stage, including Preliminary Arboricultural Reports (PARs), Arboricultural Impact Assessments (AIAs), and Tree Protection Plans (TPPs). These reports are developed in line with the AS 4970:2025 structure and are accepted by councils across Melbourne. You’ll get the documentation you need to satisfy planning conditions—without unnecessary delays or revisions.

2. On-Site Tree Protection and Supervision

TLC Trees provides practical, on-site support to ensure your construction activities stay within the protection guidelines. From installing fencing and signage to supervising root investigations, pruning and trenching, we’re there to make sure your team does things right. Our arborists are qualified, experienced and fully equipped to provide real-time solutions if issues arise during the build.

3. Expert Advice at Design Stage and Beyond

We don’t just respond to problems, we help you prevent them. Our team works closely with your planners, architects and engineers to recommend design-friendly tree retention strategies, minimise encroachments, and plan effective mitigation when space is limited. With TLC Trees involved from the beginning, you reduce the risk of costly redesigns and keep your project moving forward.

Whether you’re managing a residential build, a multi-unit development or a commercial site, our goal is simple: to protect valuable trees, reduce compliance risk and keep your project on schedule. With AS 4970:2025 now in full effect, having the right arborist on your side is more important than ever.

Frequently Asked Questions (FAQ)

Do I need an arborist for a small renovation or extension?

Yes, if there are trees on or near the property that could be impacted. Even minor works like driveway widening or fence installation can disturb root zones. Councils may require an arborist report to assess tree viability, especially for regulated or native trees.

Can I just remove a tree if it’s in the way of construction?

Not without checking local planning overlays and getting approval. Many councils in Melbourne protect native or established trees, and removing one without permission can lead to fines. An arborist can help determine if the tree is protected and what alternatives may be available.

What’s the difference between a general tree lopper and a qualified arborist?

A tree lopper focuses on cutting and removal, often without formal qualifications or understanding of standards like AS 4970:2025. A qualified arborist is trained in tree biology, structure and care, and provides detailed assessments, reports and compliant protection plans.

What happens if construction damages a protected tree accidentally?

Damage to roots, trunk or canopy can result in council enforcement, fines or even legal disputes if the tree was subject to a planning condition. Councils may also require remedial action or compensation. Engaging an arborist to supervise site activity helps prevent these issues.

Can an arborist help get my building permit approved faster?

Yes. Councils now expect high-quality documentation that aligns with AS 4970:2025. A professional arborist report submitted early can answer key planning questions, reduce back-and-forth with council and improve your chances of a fast, smooth permit approval.

Final Thoughts

AS 4970:2025 marks a major shift in how trees are managed and protected during development across Melbourne and the rest of Australia. With clearer guidelines, stricter compliance measures and a focus on early arborist involvement, this updated standard encourages smarter planning and better environmental outcomes.

For developers, builders and property owners, this is not just about ticking boxes. It’s about building with foresight, reducing project risk and creating spaces that respect the long-term value of mature trees. Integrating tree protection from day one can save time, money and stress and lead to better results for both your project and the surrounding environment.

At TLC Trees, we’re ready to help you meet these new requirements with confidence. From tailored arborist reports to on-site protection and design guidance, we partner with you to make compliance simple and stress-free.

Need help with tree protection for your next project?

Contact TLC Trees today to book a site assessment or request an arborist report aligned with AS 4970:2025.