NRZ encroachment calculator
Work out what proportion of the notional root zone a proposal occupies, and how that classifies.
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Calculate
Encroachment into the root zone
Give the distance from the trunk to the works and the encroached area is worked out for you, then classified against the notional root zone as minor, moderate or major.
1The tree
Where exactly do I measure?
- Level groundMeasure the diameter 1.4 m above ground level.
- Sloping groundTake ground level on the upslope side, then measure 1.4 m above that.
- Leaning trunkMeasure 1.4 m along the lean, not 1.4 m vertically off the ground.
- Fork above 1.4 mOne trunk at that height, so measure it as a standard tree.
- Fork below 1.4 mEach stem is measured, then combined. Use the multi-stemmed tree type.
- Buttressed treeMeasure just above the buttress, where the trunk stops widening into the roots.
Enter a trunk diameter and the notional root zone appears here.
2Structural root zoneOptional
Enter the buttress diameter and the structural root zone appears here.
3The proposed works
A straight edge — a slab, wall or footing
The encroachment needs a trunk diameter in step 1 first.
Your figures
Enter a trunk diameter and the zones appear here. Nothing on this page is a Tree Protection Zone — that is determined by a project arborist.
- NRZ radius
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- NRZ area
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- From DSH
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- SRZ radius
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- Encroached area
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- Encroachment
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- It does not give you a Tree Protection Zone. The notional root zone is the calculated starting point; the final TPZ is determined by a project arborist after considering the tree, the site and the proposed works.
- It does not tell you whether a development complies, whether a council will approve anything, whether a tree can be removed, or whether works are safe to proceed.
- It does not replace a site inspection. The measurements have to be taken on the tree, and site-specific professional assessment may still be required.
- It does not handle palms, cycads or tree ferns, because the supplied Standard does not support applying the standard method to them.
- The shapes are simplified — a straight edge, a right-angled corner and a straight trench. Real works are rarely that tidy, and an irregular footprint needs the area worked out from the plan.
- It classifies one tree against one proposed encroachment. A site with several trees, or works reaching more than one root zone, is an assessment rather than a calculation.
Common questions
About this calculator
The part of the notional root zone the proposed works occupy. That includes the footprint of what is being built, and the ground disturbed to build it — excavation, access and level changes all count even where nothing permanent ends up there. You give the distance from the trunk to the works and the area is calculated from it, so measure to the edge of the disturbance rather than to the wall.
Because where the encroachment sits matters as much as how large it is. Anything intersecting the structural root zone is major regardless of percentage, since those roots are what hold the tree up.
Because the percentage fell in the minor band but the root zone has already been encroached, or it is not known whether it has. A previously encroached zone does not carry the same tolerance, and the supplied rules do not resolve that case automatically. Returning a confident "minor" there would be false certainty.
For minor and moderate encroachments, an equivalent area considered elsewhere around the tree. It is shown for information only and it does not redefine the final Tree Protection Zone.
No. A classification is one input into an assessment, not an approval. It does not establish that a proposal complies, that a council will accept it, or that the tree will be unaffected.
Contact
Send Adam the address and he will take it from there
For many protected vegetation questions, the property address is enough to start checking. Call, or send the details below.