Tree Root Protection Questionnaire.

TRP Panels require an evenly graded subbase layer, which can be made up to any high points with granular, permeable fills such as crushed stone (CORE SubFlow20 or 6), sharp sand or clean graded soil, dependant on depth of fill required.

No, standard separation membranes do not have the adequate tensile strength required for tree root protection. A specialist TRP membrane should be used below the system, they have high tensile strength and help maintain water and gaseous exchange.

CORE TRP Geogrid is an additional 2-dimensional support layer that helps to distribute the traffic load further, preventing the fill material within the cells from puncturing the specialist TRP membrane when exposed to extremely heavy traffc loads.

The fill material is one of the most important elements of the TRP system. The TRP Panel should be filled with a SUDS compliant free draining subbase material such as CORE SubFlow20 or SubFlow40 (a cohesive angular 4/20mm or 20/40mm mix that has been screened and washed to create a ‘reduced fines’ infill that remains porous even after compaction within the cellular structure).

The depth of TRP panel required depends on the intended traffic loads. The heavier the traffic or softer the subsoil, the deeper the panel will need to be to sufficiently distribute the load. Please refer to page 17 for guidance and consult your arborcultural advisor.

BS 5837 recommends a minimum distance of 500mm between new surfacing and buttress roots. There may be scope for flexibility in this separation for mature trees with little potential for future growth, if agreed by the supervising arboriculturist.