PAR or AIA — or both?
You’ve been told you need “an arborist report” for your DA. The architect mentioned a PAR; council said something about an AIA; your last project used an AIA but this one has a different scope. Which do you actually need?
This is the most common pre-DA arboricultural question. The short answer: they’re not interchangeable, they’re sequential. Each is the right answer at a different point in the project. Choosing the wrong one wastes money and time.
In this post
What’s in a PAR
A Preliminary Arboricultural Report is the early-stage report. It identifies the trees on and around your site and produces the constraint information your design team needs before the building footprint is locked in.
Typical PAR contents
- On-site tree inventory: species, dimensions (DBH, height, canopy spread), condition rating
- AS 4970-2025 calculations for every tree: NRZ radius, SRZ radius
- Retention value rating per tree (high / medium / low)
- Site plan with protection zones overlaid — the constraint map for the design team
- Plain-English commentary on design implications
- Council pre-DA briefing pack
What a PAR does not do: classify encroachment, prescribe specific mitigation, generate a replacement-planting schedule, or produce a Tree Protection Plan. Those are AIA outputs.
Think of a PAR as “these trees exist; here’s where they can’t be touched; design around that”.
What’s in an AIA
An Arboricultural Impact Assessment is the DA-stage report. It takes a specific design (the building footprint, driveway, services, earthworks) and quantifies the impact on each retained tree under AS 4970-2025.
Typical AIA contents
- Everything that’s in a PAR (tree inventory, dimensions, NRZ / SRZ calculations)
- Encroachment classification per tree: Minor / Moderate / Major
- Mitigation protocols specific to each tree’s encroachment tier (air spade investigation triggers, root pruning protocol, ground protection specification)
- Replacement planting schedule per council DCP requirements
- Tree Protection Plan (TPP) site plan with TPZ fencing, no-go areas, supervision schedule
- Council-ready written report with photographs and signed declaration
An AIA presupposes a design. It tells you what the proposed design does to the trees; it doesn’t tell you how to design.
Think of an AIA as “these are the trees, this is the proposed design, here’s what happens to each tree, here’s how to mitigate”.
When you need a PAR
A PAR is the right report at concept stage when the design is still flexible. Specific situations:
1. Site purchase due diligence
Before buying, you want to know what trees are on the site, which need to be retained under council DCP, and what the design constraints will be. A PAR gives you that without committing to a specific design.
2. Concept / feasibility design
Architects working on a concept design need to know the TPZ footprints before sketching the building layout. A PAR done early in concept saves redesign work later.
3. Early design (footprint still flexible)
If you’re still moving rooms around, considering different building positions, or evaluating two or three layout options, a PAR informs each option. The cost of one PAR is much less than the cost of an AIA you have to redo when the design shifts.
4. Subdivision feasibility
For subdivision DAs, the PAR identifies tree constraints across the whole site, which informs lot layout, road access, services routing. Done before the subdivision design, not after.
For all four scenarios, the alternative — commissioning an AIA on a non-final design and then redoing it when the design changes — costs more in total and adds weeks to the timeline.
When you need an AIA
An AIA is the right report at DA stage, with a locked or near-locked design. Specific situations:
1. DA submission with retained trees
Most NSW councils require an AS 4970-2025 AIA for any DA where retained trees are within the proposed works’ TPZ. The AIA is the council’s primary tree-impact evidence for the DA.
2. Late design / construction certificate preparation
Where the design is finalised but DA hasn’t been lodged, the AIA goes alongside the architectural and engineering drawings.
3. RFI response on an existing DA
If council issues a Request for Information specifically about tree impact, the AIA is what closes the RFI. Faster than starting from a PAR.
4. After-the-fact for unauthorised works
Where works have already begun without an AIA and council is investigating, a retrospective AIA documents the current state of the trees and the works done. Often part of a remediation plan.
When you need both (staged approach)
For any project with multiple trees or significant trees, the cost-effective path is staged:
- PAR at concept / early design — informs the building footprint, captures the constraints, avoids designing around trees that aren’t actually protected.
- AIA at DA stage — takes the locked design and quantifies impact per tree. The PAR’s data is reused; only the design-specific impact analysis is new work.
Doing both staged is typically cheaper than doing an AIA alone twice (which is the common failure mode when the AIA is commissioned too early and the design shifts).
The most common mistake. Commissioning an AIA before the design is locked in. If the building footprint shifts (a common outcome of a thorough PAR), the AIA has to be redone — you pay twice. For greenfield sites, sites with multiple significant trees, or any project where the design is still flexible, do the PAR first.
Cost and timing
| PAR | AIA | PAR + AIA staged | |
|---|---|---|---|
| When in the project | Concept / early design | DA stage | Staged across both |
| Indicative cost (NSW) | $1,500 – $2,500 + GST | $1,800 – $3,500 + GST | Combined $3,000 – $5,500 with discount |
| Indicative turnaround | 5 – 7 business days | 7 – 14 business days | Same as individual |
| 11+ trees / heavily vegetated | Scoped per tree count | From $2,500 + GST or more | PAR informs the AIA scope |
| Council-accepted for DA? | Only as pre-DA / supporting | Yes – primary DA document | Yes (AIA is the DA evidence) |
Note that costs scale with complexity. A simple single-tree report on a residential site sits at the bottom of the range; a multi-tree site with significant trees, complex access, or council-specific reporting requirements sits at the top. Final scope confirmed after site review.
Use the PAR vs AIA decision tool
If you want a quick answer without reading the whole post, our PAR vs AIA Decision Tool is a 5-question wizard that routes your specific project to the right report (PAR, AIA, both staged, standalone TPP, expert witness, or “no report needed”). Includes indicative cost banding and turnaround for each outcome.
5-question wizard: PAR or AIA?
Stage, project type, tree count, significant trees, driver. Indicative cost and turnaround for each pathway. Free PDF summary for your council pre-DA meeting.
Once you know the report type, our TPZ Calculator gives you preliminary AS 4970-2025 numbers for your trees — useful for council pre-DA meetings or to brief your architect.
FAQ
My council didn’t specifically ask for an AIA – do I still need one?
If your works are within the Tree Protection Zone of any tree on the site, neighbour property or street verge, most NSW councils require an AS 4970-2025 AIA under the local DCP. Pre-DA enquiry to council confirms the specific requirement for your project. Submitting a DA without an AIA where one is required is a common RFI trigger and adds weeks to the timeline.
Can the PAR and AIA be combined into one report?
For very small sites (1-2 trees, simple design) yes. For anything larger, the value of the PAR is in informing design before lock-in, so combining them defeats the point. Most multi-tree NSW projects benefit from staging.
What’s a Tree Protection Plan (TPP) and how does it fit in?
The TPP is the construction-stage document – drawn site plan with TPZ fencing layout, ground protection, signage, supervision schedule. Usually a deliverable of the AIA (included in the scope). Can be commissioned standalone post-DA when council has made tree protection a condition of approval and the AIA didn’t include construction-stage drawings. Standalone TPP from $1,200 + GST.
Does the AIA replace the need for a Project Arborist on site?
No. The AIA is design-stage; the Project Arborist is construction-stage. Most NSW DAs with retained trees require both – an AIA as part of the DA, plus a named Project Arborist for site supervision. The same consulting arborist can perform both functions if engaged for the project.
How long is an AIA valid for?
Most NSW councils accept an AIA for 12-24 months from the date of inspection, provided site conditions don’t materially change. If the DA process drags on, council may ask for an updated inspection – the tree dimensions and AS 4970-2025 calculations don’t typically change, just the inspection date.
Can I commission an AIA from a tree-services company?
Most NSW councils require the AIA to be written by a qualified consulting arborist at AQF Level 5 (Diploma of Arboriculture) or equivalent. A tree-services company holding only AQF Level 3 (Certificate III) typically can’t write a council-accepted AIA – their qualification is for pruning and tree work, not for assessment and reporting.
Note. This is general educational content. Specific council requirements vary by LGA. For your project, run the decision tool or call Assurance Trees for a 15-minute scoping conversation before committing to either report type.
Need a PAR or an AIA?
Assurance Trees writes Preliminary Arboricultural Reports + Arboricultural Impact Assessments to AS 4970-2025 across NSW. AQF Level 5 Consulting Arborists, NSW Licensed Builder, in-house GIS. Quote in 24 hours.
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