Ground protection within a root protection area

Ground protection is what you specify when construction traffic has to cross a root protection area and fencing it off is not an option. It is not a lesser form of protection. Section 6 of BS 5837:2012 treats barrier fencing and ground protection as alternatives chosen according to what has to happen on that piece of ground, and an arboricultural method statement that proposes ground protection for a route the site actually needs is more likely to be approved than one that fences everything and is quietly ignored in week three.

The root protection area itself is a calculated figure: a circle of radius twelve times the stem diameter for a single stemmed tree, capped at 707 m². Its shape can be adjusted where soil conditions and likely root distribution justify it, provided the area stays the same. Inside that line, the soil is the asset you are protecting.

When ground protection replaces fencing

Fencing is the default because it keeps everything out. Ground protection is the answer where something has to get in: a temporary haul route, a crane position, a scaffold zone against a facade, a delivery bay, an area where a piling rig has to stand.

The test an arboriculturist applies is whether the activity can be moved. If it can, move it. If it cannot, the protected route is designed, drawn and built before any plant crosses the line, and the fencing is arranged around it so the only way into the root protection area is over the protection.

What ground protection is defending against is compaction and rutting. Roots need gas exchange and water movement through soil pores, and a loaded wheel closes those pores in a way that does not recover on its own. The visible damage appears in the canopy two or three seasons later, long after the contractor has left.

Build-ups and what each one carries

The British Standard sets out a range, and the right choice depends on the load and the duration.

The principle running through all three is the same. A geotextile separates the existing soil from anything placed on it, so the surface can be lifted cleanly afterwards. A load spreading layer distributes wheel or foot loads over an area large enough that ground pressure stays below the level at which the soil structure collapses. And nothing is excavated, because the point is to work above existing levels.

For the heavier cases, get an engineer to size the granular layer against the actual plant loading rather than copying a thickness from another job. A tracked excavator and a concrete wagon impose very different pressures, and a specification written for the first will fail under the second.

Getting the drawing and the method statement right

Two documents carry the specification, and both are usually secured by condition.

The tree protection plan shows the retained trees, their root protection areas, the barrier positions and the extent of ground protection, drawn to scale over the construction layout. The arboricultural method statement describes the build-up, the sequence, the loading limits, the duration and the supervision regime. Where either is missing, expect a condition requiring it before development starts, which is the point at which the programme slips.

Include these in the method statement:

1. The build-up in section, with the geotextile, the load spreading layer and the surface named by product type or specification.
2. The maximum axle load or plant type permitted on the protected route.
3. The sequence: protection installed and inspected before any other site activity within the root protection area.
4. The inspection and reporting regime, with the project arboriculturist named and the reporting interval stated.
5. The conditions under which use stops, typically prolonged wet weather or evidence of rutting.
6. The removal and reinstatement method.

The Arboricultural Impact Assessment should already have identified which trees are worth this effort, using the category grading in the British Standard. Spending money protecting a category C tree with eight years of useful life left, while a category A specimen sits unprotected on the other side of the site, is a mistake that gets noticed at appeal.

Loading, duration and the weather

Three variables decide whether protection works in practice.

Load is the obvious one, and it is managed by specifying the plant allowed rather than by trusting a site manager to judge. Write it into the method statement and repeat it on the site induction.

Duration matters more than people expect. A protected route in place for eight months holds soil in darkness under a sealed surface, changing moisture and temperature conditions. Where a route is needed for a long period, allow for the surface to be lifted periodically where practicable, and plan the reinstatement carefully.

Weather is the variable that catches sites out. Saturated soil compacts at far lower loads than dry soil, and winter trafficking over a route designed on a dry summer assessment is how damage happens despite a correct specification. A trigger in the method statement that suspends use when the ground is waterlogged costs nothing to draft and protects both the tree and the contractor.

Illustrative example: a site with a category A oak on the southern boundary needs a delivery route across the outer third of its root protection area. The project arboriculturist specifies a geotextile, a 150 mm granular layer and interlocking steel plates, with use limited to rigid vehicles and a suspension trigger after two consecutive days of heavy rain. Fencing surrounds the rest of the root protection area. Monthly supervision reports go to the authority. Dimensions and details are illustrative, and any real specification needs to be designed for the site.

Taking it up again

Reinstatement is part of the specification, not an afterthought. Lift the surface and the load spreading layer, remove the geotextile, and inspect the soil underneath. Where compaction has occurred, decompaction using compressed air soil injection is the usual remedy, followed by a mulch layer to restore organic matter and moderate moisture loss.

Then record it. A short completion report from the project arboriculturist, with photographs and a note of any incidents during the works, is what discharges the condition and closes the file. It is also the document that protects the developer if a tree declines two years later and someone asks why.

Where the protected route crosses the public highway or involves work near street trees, the position is different again, because the highway authority and the utility undertakers have their own regimes, covered in our note on street trees, highway works and utility trenching. The wider sequencing question, which is how to keep a retained tree alive through a whole construction programme rather than one activity, is dealt with in retaining a tree through a construction programme.

One honest caveat. The British Standard gives recommendations, not a code, and it expects professional judgement to be applied to the particular tree, soil and loading. A specification lifted wholesale from another project is the most common reason ground protection fails to protect anything.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Browse the report types to see what a tree-constrained site usually needs alongside the arboricultural work.