RPA for Veteran Trees


Section 4.6 of BS 5837:2012 provides a methodolgy for calculating the Root Protesction Area (RPA) for trees and KeyTREE uses this to calculate the RPA that is drawn. For single stemmed trees, this is based on 12 times the stem diameter but there is widespread debate that veteran trees are more likely to have a larger RPA and 15 times the stem diameter would be more appropriate.

You would like to know how to draw an RPA for veteran trees based on this higher, or different, calculation method.


When using the "BS Calculated" option, there is no option within KeyTREE to change the the calculation method for detemining the drawn RPA. To draw RPAs for veteran trees, where a differnt calcuation method is required, please continue as follows:

  • Manually calculate the radius of the RPA required, based on the stem diameter and your preferred calculation, e.g. stem diameter x 15 (for veteran trees)
  • Add or modify a tree and next to "Root / RPA", select the [...] elipsis

  • Below RPA, change the option from "BS Calculated" to Radial and enter the RPA radius determined from your calculation

  • Pick OK to apply the change and return to the Add of Modify Tree dialog.
  • Pick OK to apply these changes and return to the drawing
  • The RPA will draw now based on the radius you have entered

NOTE: You are not able to apply an RPA incusion when using this method but you can set the RPA dropdown to Geometry and either draw the estimated RPA, including the incursion, or use "From Drawing" if the RPA with the incursion has already been drawn using standard AutoCAD geometry.