Compiled Approved plans MCU22/0087.01 & OPW22/0140.01

                                                                                                   Consult Arborist

                 7.2 CALCULATING TREE PROTECTION
                 The descriptions of the Tree Protection Zone (TPZ) and Structural Root Zone (SRZ) are from
                 the Australian Standards, AS 4970-2009 Protection of trees on development sites. These
                 descriptions provide the basic prerequisites to calculate the TPZ and SRZ, and the
                 compensates for when encroachment or a reduction in the size/area of the TPZ is required to
                 facilitate a development: see Appendix D of the Australian Standard AS 4970-2009.

                 Many factors need to be taken into consideration when estimating tree root growth and spread.

                 7.2.1 TREE PROTECTION ZONE (TPZ)
                 As specified in the Australian Standard, AS 4970-2009, the TPZ is the principal means of
                 protecting trees on a development site. The TPZ calculates the radius of a circular area
                 combining the root and crown spread of a tree for protection and isolation from construction
                 disturbance so the tree can remain in a viable condition for the future. The TPZ incorporates
                 the SRZ.

                 DBH = Diameter at Breast Height - trunk diameter measured at 1.4m above ground

                 TPZ RADIUS = Twelve times the DBH

                 Example: .5m DBH x 12 = 6m TPZ RADIUS.

                 A TPZ should not be less than 2m or greater than 15m unless additional crown protection is
                 required.

                 7.2.2 STRUCTURAL ROOT ZONE (SRZ)
                 The SRZ, as specified in AS 4970-2009, is the minimum surface area of protection required
                 around a tree to maintain that tree’s stability – a larger area than this is required to maintain a
                 tree in a viable condition for the future. It is only necessary to calculate the SRZ when major
                 encroachment into a TPZ is proposed.

                 An indicative SRZ RADIUS can be determined from the lower trunk diameter (above the root
                 buttress), D, measured in metres and applying the following formula:
                                                                       0.42
                                                     RSRZ = (D x 50)          x 0.64

                 The SRZ RADIUS for trees with a trunk diameter less than 0.15m will automatically be 1.5m.


                  Please note that these are theoretical calculations and are to be used as a guide. Large tree
                  species, particularly Fig trees, will have woody structural and feeder roots that extend to a
                  greater distance than the calculations. Trees within urban environments where solid
                  structures restrict root growth can also alter a tree’s root spread and direction. An additional
                  water/food source would also encourage roots to grow further than expected.




                 22_12_01_AIA_Thynne_37 Bottlebrush Ave                                                Page 15 of 21
Document Set ID: 24320610
                  22595441
Version: 1,
         2, Version Date: 20/11/2025
                          25/09/2023