Arboricultural Impact Assessment Report

Sometimes. Where a tree has genuinely low retention value — poor health, poor structure, short useful life expectancy — the assessment can build an evidence-based case for removal. What it cannot do is manufacture a justification for removing a healthy, high-value tree. An honest read early is far cheaper than a redesign after refusal.

Before. Tree constraints identified at concept stage are a design input. Identified after the drawings are done, they become an expensive redesign.

Under AS 4970:2025, the Tree Protection Zone is the area set aside and fenced off to protect a tree’s roots and crown during the build. The project arborist sets it, starting from the Notional Root Zone (12 × the trunk diameter, the circle that used to be called the TPZ) and adjusting it for where the roots actually are. It matters because it is what your builder has to protect, while how far your works reach into the NRZ (up to 10%, 10 to 20%, or past that) decides whether the design goes ahead as drawn, has to be justified, or has to change. Work out the NRZ and SRZ for your tree.

All three come from AS 4970:2025. The NRZ (Notional Root Zone) is the calculation: a circle around the trunk with a radius of 12 × the trunk diameter, measured 1.4 m above the ground, and never less than 2 m or more than 15 m. Before the 2025 edition, that circle was called the TPZ. The SRZ (Structural Root Zone) is the smaller area close to the trunk holding the tree upright, worked out from the diameter just above the root buttress, and any encroachment into it is major. The TPZ (Tree Protection Zone) now means the area actually fenced off and protected on site, set by the project arborist from the NRZ and adjusted for where the roots really are. Encroachment is measured against the NRZ; the TPZ is what your builder protects. What changed in AS 4970:2025.

It is an impact assessment whose conclusion is that a tree cannot viably be retained — the same root zone calculations and the same encroachment analysis, with a different answer at the end. If the tree is coming out and there is no construction involved at all, the document you actually need is an arborist report.

From $1,100 including GST, delivered in 5-7 business days. The figure scales on the number of trees and the size of the site rather than the value of the build, and a fixed quote follows once the plans have been reviewed. The full price list and a cost calculator are on the pricing page.

All of them in substance, though the name on the information request varies. Brisbane City Council asks for one where works will significantly impact protected vegetation; the other South East Queensland councils arrive at the same requirement through their planning scheme vegetation codes and overlays. What triggers it is the works falling inside a protected tree’s root zone rather than which council you are in — the rules for each council set out the local wording.

The line is what you are doing to the tree, not how big the job is. Removing a tree means an arborist report, from $660. Building near a tree that is staying means this one, from $1,100. Being quoted for the first when council wants the second is the most common and most expensive mix-up in this work.

What differs is the subject. An arborist report assesses the tree — species, condition, structure, and the case for the work. An impact assessment assesses your proposal against the tree: root zones calculated under AS 4970:2025, encroachment measured off your drawings, and a protection specification the site team has to build to.

Where a development does both — one tree out, three staying — the impact assessment covers all of it and you do not need two documents. The report picker settles it in two questions if you are still unsure.