Get clear on TPZ so you can plan works near trees with less risk, fewer surprises, and fewer approval delays.



What you’ll learn: what a Tree Protection Zone is, how TPZ is typically calculated in Australia, what “encroachment” really means on site, and the practical steps that help keep projects moving.

• What TPZ is, and why councils and certifiers care
• How TPZ is calculated, and common measuring mistakes
• What happens if you need to work inside a TPZ
• How a Tree Protection Plan supports construction compliance

What is a Tree Protection Zone (TPZ)?

A Tree Protection Zone is the area around a tree that should be protected during development, construction, or site works.



It exists to reduce the chance of tree decline, instability, or failure caused by root damage, soil compaction, or changes to levels and drainage.

TPZ vs SRZ, what’s the difference?

You’ll often hear two related terms:

• TPZ (Tree Protection Zone): a practical protection area used for planning and site controls.
• SRZ (Structural Root Zone): a smaller zone focused on the roots most critical for tree stability.



On real sites, both matter, but TPZ is usually the starting point for design layout and construction controls.

When TPZ matters on a project

TPZ comes up any time works are proposed near existing trees, especially where approval, permits, or compliance documentation is required.



Common triggers include:

• new builds, extensions, and multi-dwelling projects
• driveways, crossovers, paths, decks, and pools
• excavation, cut and fill, and retaining walls
• trenching for services like stormwater, sewer, power, NBN, irrigation
• demolition access, crane pads, scaffolding zones, and material laydown areas

If you are unsure whether tree constraints will affect your design or program, a Tree Protection Plan can clarify what must be protected and how it will be managed on site. See Tree Protection Plan.

How TPZ is typically calculated in Australia

TPZ is generally derived from trunk diameter, then expressed as a radius measured from the centre of the trunk at ground level.

The commonly used method sits within the Australian Standard for tree protection on development sites. You can view the standard listing here: AS 4970:2025, Protection of trees on development sites.

Step 1, measure the trunk correctly

Most TPZ calculations start with trunk diameter measured at breast height, typically 1.4 m above ground.



If the tree is multi-stemmed, or has a flare or buttress, the measurement approach can change. That is where mistakes often happen.

Step 2, apply the TPZ method used for planning

A common planning method expresses the TPZ radius as a multiple of trunk diameter.

This gives you a protection radius you can plot on plans and test against:

• building footprints
• excavation extents
• service alignments
• temporary works and access

Step 3, plot it on the right drawings

TPZ only helps if it is shown clearly on the same plans being used for approvals and construction, including:



• site plan and set-out
• demolition and temporary works
• services and drainage
• earthworks and retaining

TPZ rules for building near trees, what “encroachment” means

Encroachment usually means you are proposing works inside the TPZ.

That does not automatically mean “no”, but it does mean the design and construction method need to be assessed properly.

Typical factors that influence whether encroachment is feasible include:

• the tree species, age, health, and structure
• soil conditions and slope
• how much of the TPZ is affected, and where
• the type of impact, excavation is different to a pier and beam system
• whether roots can be retained, bridged, or managed safely



Where impacts are likely, an Arboricultural Impact Assessment can document what is proposed, what the risk is, and what controls are needed.

Why TPZ matters, beyond approvals

Tree damage problems often show up later, not during the build.

Root damage and soil compaction can lead to:

• canopy dieback and decline over months
• loss of stability after wet seasons and storms
• pest and disease entry points
• disputes around responsibility and rectification



A clear TPZ approach supports smoother approvals, cleaner site compliance, and fewer avoidable tree-loss outcomes.

What a Tree Protection Plan actually does

A Tree Protection Plan translates “protect the tree” into site-ready controls.

It commonly covers:

• tree protection fencing locations and specifications
• exclusion zones for machinery, storage, and washout
• requirements for excavation near trees
• controls for service trenching and crossings
• inspection, supervision, and sign-off points during construction



Good TPZ controls are simple, visible, and easy for a site team to follow.

Practical examples that commonly cause TPZ issues

Driveways and crossovers

These often clip the TPZ because they run close to the front boundary.

Options may include:



• adjusting alignment and widths early
• using construction methods that reduce excavation
• locating piers or supports to avoid critical root zones

Services and trenching

Trenching can be one of the biggest hidden risks.

Where services must pass near trees, controls can include:



• rerouting to avoid sensitive areas
• using non-destructive methods where appropriate
• staged works with supervision and root management

Cut and fill, retaining walls, and level changes

Changing levels inside a TPZ can alter soil conditions and root function.

Key risks include:



• burying roots under fill
• exposing roots with cut
• changing drainage patterns and waterlogging

FAQ

What is a Tree Protection Zone in simple terms?

It is the area around a tree that should be kept free from damaging activities like excavation, compaction, storage, and level changes during works.

How do I measure the tree for a TPZ calculation?

TPZ is usually based on trunk diameter measured around 1.4 m above ground. Multi-stemmed trees and buttressed trunks can need a different approach.

Can I build inside a TPZ?

Sometimes, but it needs assessment and the right construction method. Excavation, trenching, and level changes usually carry higher risk than low-impact methods.

Does a TPZ guarantee the tree will survive?

No. It reduces risk, but outcomes still depend on tree condition, site conditions, construction method, and how well site controls are followed.

What documents commonly reference TPZ on a project?

Planning drawings, landscape plans, engineering and services plans, plus the Tree Protection Plan and any impact assessment documents.

Common mistakes

• treating the tree protection fence as a rough suggestion, then moving it later
• measuring the trunk at the wrong point, or mixing up circumference and diameter
• plotting TPZ on planning drawings, but not reflecting it in construction drawings
• stockpiling soil or materials inside TPZ “just for a day”
• allowing repeated vehicle movements that compact soil inside the TPZ
• trenching through roots without a documented method and supervision

Quick checklist and next steps

Use this as a quick pre-start check:

• confirm which trees are being retained, and which are exempt or approved for removal
• measure trunks correctly, especially multi-stemmed trees
• plot TPZ on the drawings the builder and engineers are actually using
• identify any proposed encroachments early, before lodgement or final design
• choose construction methods that reduce excavation inside TPZ
• document site controls in a Tree Protection Plan and brief the site team
• schedule inspections at the right moments, not after damage has happened



The earlier TPZ is resolved, the fewer design changes and site delays you tend to wear later.

Wrap-up

TPZ is not just a line on a plan. It is a practical way to protect trees, reduce risk, and keep projects compliant during construction.



If your design, access, or services are pushing into a TPZ, the cleanest path is usually to assess the impact properly, document controls clearly, and make it easy for the site team to follow. Start with a Tree Protection Plan and link it to the wider assessment pathway when required, such as an Arboricultural Impact Assessment.

Enquire
Send your plans and site details, we will help confirm TPZ impacts and the next step.