AS 4970-2009 Calculator

The AS 4970-2009 Calculator is a free web app based on the Australian Standard® AS 4970-2009 Protection of trees on development sites. The calculator allows you to calculate tree protection zones (TPZ/SRZ) and two types of encroachment. The calculator accepts circumference or diameter measurements and can calculate DBH for multi-stemmed trees.


Calculate Protection Zones

cm
TPZ radius (m)2.0
TPZ area (m²)12.6
cm
SRZ radius (m)1.5
SRZ area (m²)7.1

Measuring DBH/DAB for a single stem/trunk tree.1


Calculate Encroachment

A
m
Distance (m) for minor encroachment (10%)1.4
TPZ radius (m)2.0
SRZ radius (m)1.5
TPZ area (m²)12.6
Encroachment area (m²)
6.3
Encroachment (%)
49.9

Encroachment Type A: Works intersecting along a straight edge.2


Footnotes
1 For further examples refer to AS 4970-2009, Appendix A, Figure A1.
2 For further examples refer to AS 4970-2009, Appendix D, Figure D1.


Glossary
DAB

(Diameter above buttress) Diameter (cm) of the trunk/stem measured immediately above the root buttress. Referred to as ‘D’ and measured in metres in AS 4970-2009.

DBH

(Diameter at breast height) Diameter (cm) of the trunk/stem measured at 1.4m above ground. For multi stem trees, refer to AS 4970-2009, Appendix A, Figure A1.

Encroachment

Any work within the protection zone of a tree, including excavation, compacted fill and machine trenching.

SRZ

(Structural root zone) An area around the base of a tree required for the tree’s stability in the ground. Woody root growth and soil cohesion in this area are necessary to hold the tree upright. Typically expressed as a radius in metres that defines a circle with the trunk/stem at its centre.

TPZ

(Tree protection zone) An area set aside for the protection of a tree’s roots and crown to provide for the viability and stability of a tree to be retained where it is potentially subject to damage by development. Typically expressed as a radius in metres that defines a circle with the trunk/stem at its centre.

Work

Any physical activity in relation to land that is specified by the determining authority (e.g. a local council).


About CAV

Council Arboriculture Victoria Inc. (CAV) is an association of arborists, tree managers and related professions working in local government in Victoria. CAV supports its members to pursue best practice arboriculture and advocates on arboricultural matters across industry and government sectors. Find out more.