Root-zone impacts
Building footprints, excavation, footings, retaining walls, fill, level changes, pavements and services are compared with each tree's Notional Root Zone and Structural Root Zone.
Arboricultural Impact Assessments · Melbourne
Test the design against the trees.
Resolve impacts before submission.
An Arboricultural Impact Assessment evaluates a developed proposal against retained trees, root zones and canopy. It identifies likely impacts and recommends practical design modifications, construction controls and protection measures.
Discuss your project
A developed proposal
From design drawings to defensible recommendations.
An Arboricultural Impact Assessment is prepared once a proposal has progressed beyond early feasibility. It compares the proposed building, excavation, levels, access, services and construction requirements with the trees that may be affected.
The assessment explains where impacts are acceptable, where more investigation is required and where the design or construction method should change to support tree retention.
The assessment process
Evidence first. Then a practical design response.
- 01
Confirm the proposal
Review the project scope, current drawings, relevant authority requirements and available arboricultural information.
- 02
Verify the trees and site
Inspect relevant trees and confirm the site conditions, dimensions and constraints that may influence the assessment.
- 03
Overlay root zones and canopy
Compare the proposal with the Notional Root Zones, Structural Root Zones and existing crown extents of retained trees.
- 04
Quantify likely impacts
Assess encroachment, excavation, fill, level changes, services, access, pruning and construction activity.
- 05
Assess tree viability
Consider tree condition, species tolerance, root distribution, site history, soil, drainage and structural stability.
- 06
Investigate uncertainty
Where needed, undertake targeted root investigation, soil assessment or further review of site and tree history.
- 07
Coordinate the design response
Recommend sympathetic design alternatives, construction methods and protection measures where practical.
- 08
Prepare the assessment
Document the impacts, viability conclusions, required changes and pathway to tree protection documentation.
What is assessed
Root, canopy and construction impacts considered together.
Canopy impacts
The assessment considers crown clearance, likely pruning, building and scaffold interfaces, crane and machinery access, retained canopy function and whether the proposed works can be completed without unacceptable damage.
Construction impacts
Access, material storage, temporary facilities, demolition, equipment movements, drainage and work methods are reviewed so practical controls can be incorporated into the project.
Illustrative moderate encroachment
Measure the impact, then test viability.
Encroachment is assessed by its area, proximity to the trunk and relationship with the Structural Root Zone. The example illustrates a 20% encroachment into the Notional Root Zone while remaining outside the Structural Root Zone.
A percentage alone does not determine the outcome. Tree condition, root distribution, species tolerance, site history, soil, drainage, construction method and the location of the impact must also be considered.
Encroachment into the Notional Root Zone
Three classifications. Different levels of arboricultural input.
Encroachment into a tree's Notional Root Zone is assessed according to the extent and proximity of proposed works in accordance with AS4970:2025 Protection of trees on development sites.
10% or less
Minor encroachment
An encroachment is minor when it affects 10% or less of the total Notional Root Zone area, is outside the Structural Root Zone and does not involve recent Notional Root Zone disturbance.
Significant impacts to tree health, structural stability or longevity are generally unlikely. Tree protection measures still apply. An equivalent area is added to the Tree Protection Zone unless the project arborist demonstrates that tree viability will not be compromised.
More than 10% to 20%
Moderate encroachment
A moderate encroachment affects more than 10% but no more than 20% of the Notional Root Zone and remains outside the Structural Root Zone.
A project arborist assesses the impact and any further investigation required to address tree viability. Design modifications or specific construction controls may be needed. An equivalent area is added to the Tree Protection Zone unless continued viability can otherwise be demonstrated.
More than 20% or within the SRZ
Major encroachment
A major encroachment affects more than 20% of the Notional Root Zone or occurs within the Structural Root Zone.
The project arborist works with the design team to develop alternatives or demonstrate continued viability. Detailed investigation may include root investigation, soil testing, tree history, research or comparable cases. A Tree Protection Plan and Tree Protection Specification should support retention, with equivalent area added unless viability without compensation is demonstrated.
Above-ground impacts
The canopy is part of the assessment.
Canopy impacts can be as important as root impacts. The assessment reviews the relationship between the existing crown and the proposed building, scaffolding, access, crane operations and other construction requirements.
Branch architecture, canopy condition, pruning tolerance and the amount and location of proposed clearance are considered. Where an acceptable outcome is possible, recommendations may include design setbacks, adjusted roof or balcony lines, controlled pruning, access restrictions or specific construction sequencing.
Design coordination
Resolve conflicts while practical options still exist.
Move or reshape the footprint
Adjust walls, decks, driveways or other works to reduce concentrated encroachment and retain functional soil area.
Change the construction method
Consider suspended, piered or bridging solutions, reduced excavation, hand excavation or non-destructive service installation where appropriate.
Investigate roots before committing
Targeted root investigation can clarify actual root distribution where it may materially affect the design or viability conclusion.
Define protection early
Identify the Tree Protection Plan, Tree Protection Specification, supervision and hold points needed to translate the assessment into site controls.
Preliminary report or impact assessment?
The project stage determines the right report.
Preliminary Arboricultural Report
Prepared before the design is fixed. It identifies trees, retention values and root-zone constraints that should inform the layout.
Explore Preliminary ReportsArboricultural Impact Assessment
Prepared once a proposal has developed. It evaluates likely impacts and the modifications, investigations and protection measures required for retained trees.
Information to provide
Current drawings make the assessment useful.
- Property address and a short description of the proposal
- Feature and level survey
- Current architectural drawings and schedules
- Civil, hydraulic, landscape, service and retaining-wall drawings where available
- Previous Preliminary Arboricultural Report or tree survey
- Council request, permit conditions or further information request
- Required timeframe and current project stage
Frequently asked questions
Impact assessment questions.
When is an Arboricultural Impact Assessment prepared?
It is usually prepared after a concept or developed design is available, so the proposal can be assessed against the trees, root zones, canopy and construction requirements.
Is every encroachment unacceptable?
No. The extent, location and nature of the impact are considered together with tree condition, root distribution, species tolerance, site history and construction method. Some impacts can be addressed through design modification, investigation and protection controls.
What happens when the encroachment is more than 20%?
It is classified as major encroachment. More detailed arboricultural investigation is required, and the project arborist works with the design team to develop alternatives or demonstrate that the tree can remain viable.
Are canopy impacts included?
Yes. The assessment considers crown clearance, likely pruning, building and scaffold interfaces, construction access and the ability to retain a functional canopy.
Will the report include design recommendations?
Yes. Where practical, the assessment identifies sympathetic alternatives such as adjusted footprints, reduced excavation, different footing systems, modified levels, redirected services or controlled construction methods.
Does an AS4970:2025 aligned report guarantee approval?
No. The report provides arboricultural evidence and professional recommendations. Planning and permit decisions remain with the relevant authority.
Start with the drawings
We will confirm the right scope.
Share the property address, current project drawings and any existing tree information or authority request.
[email protected] 0401 766 127Consulting across Melbourne & Victoria
Subject to service-area eligibility.
Service area note: Consulting work cannot currently be accepted for properties within Maroondah municipality due to a professional conflict-of-interest requirement.