Offsetting Root Protection Areas
For Trees Near Built Infrastructure

Offsetting Root Protection Areas (RPAs) involves adjusting the protective zones around trees during development projects to safeguard their root systems while accommodating construction activities.

Trees growing in an urban environment and in close proximity to built infrastructure such as boundary walls, areas of hard standing and building foundations can pose a tricky constraint to development design. Many assume that tree roots will not be found growing in such inhospitable conditions and disregard them as a material constraint to development. However, our team of arboricultural consultants all too often come across roots in the most unusual places.

Our consultants worked closely with a local architect on a project in south west London that involved a large Sweet chestnut, sited in a footway but within close proximity to the sites boundary wall. Tree roots can be heavily influenced by built infrastructure as they will naturally follow the path of least resistance toward a favourable growing medium. Therefore predicting the root protection area of trees sited in close proximity to built infrastructure can be very difficult from an above ground visual assessment alone. A root protection area is a layout design tool indicating the minimum area around a tree deemed to contain sufficient roots and rooting volume to maintain the tree’s viability and where the protection of the roots and soil structure is treated as a priority.

In order to make an informed decision regarding the sites feasible development area, the projects architect was keen to understand the constraint posed by this third party tree. Our arboricultural team completed a series of trail trenches using air displacement equipment (air lance or air spade) to reveal the location of roots sympathetically and without causing damage to the delicate root bark. Following completion of these trenches, our arboricultural consultants produced a detailed Tree Constraints Plan that included an ‘offset’ root protection area for the Sweet chestnut, that would allow the architect to develop a detailed design. As opposed to a typical circular root protection area, an offset root protection area is commonly presented as a polygon and takes rooting constraints on site into consideration.

By completing the above process, our arboricultural consultants provided the architect with an accurate Tree Constraints Plan that clearly and accurately depicted the constraint posed by the  third party tree. This allowed for a detailed design to be created that safeguarded the tree but also utilised the maximum development area available on site. Please follow the link below to our free guide to developing land with trees.

https://www.pjcconsultancy.com/wp-content/uploads/2017/03/Planning-Arboriculture-Complete.pdf

If you are working on a development opportunity and require an arboricultural survey, please get in contact and one of our experienced arboricultural consultants today.