Root Protection Zone Foundations for a Garden Room in Surrey

When building near protected trees, the foundation design must comply with strict arboricultural and planning conditions. Preformed Substructures Ltd provide low-impact Root Protection Zone (RPZ) piling solutions that allow construction without damaging tree roots.

Project Summary

A client in Surrey required a traditionally build brick and block walled garden room for use as a small office located within the Root Protection Area (RPA) of a mature protected tree. Site excavation was restricted, so a non-invasive piling method was needed.

root protection zone

Step-by-Step Project Delivery

  • 1

    Arboricultural Review

    We reviewed the tree survey, RPA measurements and planning conditions requiring low ground pressure and minimal excavation.

  • 2

    RPZ Foundation Strategy

    Our engineers specified high load capacity GoliathTech helical screw piles positioned carefully to avoid significant root structures. A suspended galvanised steel beam with beam and block infill was used to span over sensitive areas.

  • 3

    Root Mapping & Hand Excavation

    Trial pits were hand dug to identify key roots. Pile positions were adjusted to ensure zero root severance.

  • 4

    Low-Impact Pile Installation

    We used a lightweight pile installation equipment positioned on ground protection mats to avoid soil compaction.

  • 5

    Suspended Ground Beam Construction

    Steel beams were installed a minimum of 150mm ground level, ensuring tree roots remained undisturbed and airflow could circulate below.

  • 6

    Arboricultural Sign-Off

    We provided photographs, pile logs and RPZ compliance documentation to the local authority.

Results

The protected tree remained healthy, and the client achieved planning compliance without delay.

Building Near Protected Trees?

Preformed Substructures Ltd offer professional RPZ piling solutions across London & the South East. Read more about our screw pile installation service or get in touch today