Once the layout and AIA are agreed, BS5837 expects a detailed Tree Protection Plan (TPP) to show exactly how retained trees will be safeguarded during works. This plan is superimposed on the topo and layout, so everyone can see protection in the context of buildings, levels and services.
The TPP should:
- Show all retained trees, their crowns and RPAs on the final layout.
- Plot the line of all protective fencing, forming construction exclusion zones.
- Show where ground protection is needed inside RPAs for temporary access.
- Identify any extra physical measures such as tree protection boxes around stems.
Barrier and ground‑protection lines should be drawn as polygons, dimensioned from fixed features so they can be accurately set out on site.
Tree Protection Fencing: Default and Lighter Options
BS5837 sets out a “default” heavy‑duty barrier: scaffold poles in a rectangular frame, braced and supporting 2 m weld‑mesh panels, with posts driven 0.6 m into the ground. This creates a rigid fence that reliably excludes vehicles and plant from the RPA.
Where risks are lower (for example, small‑scale works or only light plant), a lighter system of 2 m welded mesh panels on rubber or concrete feet can be used. In that case the panels should be:
- Joined with at least two anti‑tamper couplers, only removable from inside the fence.
- Braced with stabiliser struts and ground pins, or block trays where pins are not possible.
All barriers must be in place before any demolition, soil stripping or delivery of materials. They are treated as sacrosanct and should not be moved without arboricultural sign‑off and, where relevant, LPA approval.
Ground Protection: When You Must Enter the RPA
If site logistics mean you cannot keep all traffic out of part of an RPA, BS5837 allows carefully designed temporary ground protection. The aim is to prevent soil compaction, which can be caused by a single pass of heavy machinery, especially in wet conditions.
Typical ground protection systems include:
- For pedestrians only: scaffold boards over a 100 mm woodchip layer on geotextile.
- For small pedestrian‑operated plant up to 2 t: proprietary interlinked boards over 150 mm of woodchip on geotextile.
- For heavier construction traffic: engineered systems or pre‑cast concrete slabs designed with arboricultural and engineering input.
The TPP should show where existing hard surfaces are to be retained as temporary protection and where new temporary systems will be installed.
Arboricultural Method Statement (AMS): The Step‑by‑Step “How”
The AMS supports the TPP by describing in writing how sensitive work will be carried out near trees. BS5837 says it should cover any development within the RPA, or work with potential to damage retained trees.
A typical AMS includes:
- Sequence: when protection is installed, when tree works happen, and how works near trees are phased.
- Methods:
- Removal of existing surfacing and structures within RPAs.
- Installation and removal of temporary ground protection.
- Excavations using hand tools or air‑spade, and any trenchless techniques for services.
- Construction of new hard surfacing within RPAs using no‑dig or low‑dig systems.
- Installation of special foundations and retaining structures.
- Landscape preparation in protected areas.
- Monitoring: an auditable system of arboricultural site inspections and trigger points for supervision.
- Contacts: key names and details for the arboriculturist, main contractor, site manager and client.
This turns “protect the trees” into specific, measurable instructions for the site team.
Special Engineering Within RPAs: Foundations and Surfacing
Where building or surfacing within RPAs is unavoidable, BS5837 points to special engineering to limit root and soil damage. These solutions are usually reserved for good A or B category trees that would otherwise be lost.
Foundations in RPAs
Traditional strip footings can remove large numbers of roots and should generally be avoided. Alternatives include:
- Piled foundations, with root‑friendly investigation to position piles away from significant roots and beams at or above ground level, sometimes cantilevered.
- Suspended or ventilated slabs with an air void above existing soil and, if needed, redirected roof runoff under the slab, subject to building control agreement.
The design must avoid exposing roots to toxic wet concrete, so sleeved bored piles or screw piles are often preferred.
Hard Surfacing in RPAs
BS5837 recommends “no‑dig” or minimal‑dig surfacing for drives and paths in RPAs. Key principles include:
- No excavation into the soil beyond removing turf and loose organic matter by hand.
- Using three‑dimensional cellular confinement systems or similar to spread loads and avoid localized compaction.
- Limiting new impermeable surfacing in the RPA to no more than 20% of previously unsurfaced ground.
- Incorporating geotextiles, drainage and, where de‑icing salt is used, impermeable barriers and run‑off routes that protect roots.
Edge supports should avoid cutting into the root zone, using above‑ground or pinned systems like sleepers or gabions instead of deep kerb trenches.
Site Monitoring: Keeping Everyone Honest
BS5837 expects an auditable system of arboricultural site monitoring wherever tree protection measures are in place. The project arboriculturist should inspect at key stages – such as after fencing installation, before ground protection is removed, and during any RPA works – and keep records.
While the arboriculturist monitors and advises, enforcement remains with the Local Planning Authority under normal planning powers
