Street trees, highway works and utility trenching

The tree outside your site is probably not yours to deal with. Street trees sit within the adopted highway, which means the highway authority owns and manages them under the Highways Act 1980, and the planning application for your site has very little direct say over what happens to them. Anyone researching street trees highway works for the first time usually discovers this at the point where a service connection, a new access or a footway crossing has already been drawn through a tree pit.

The practical consequence is that you are dealing with two separate organisations on two separate timescales. The local planning authority handles the trees inside your red line. The highway authority handles everything beyond the back of footway, and its programme rarely matches yours.

Who holds the tree

A tree planted in the highway is normally maintained by the highway authority under its powers in the Highways Act 1980, which allow an authority to plant and maintain trees in a highway and to control what happens around them. In two-tier areas that is the county council. In unitary and London borough areas it is the same body as the planning authority, but usually a different team with a different policy document.

Tree Preservation Orders are largely beside the point here. The planning guidance on Orders is directed at trees in private ownership, and street trees are dealt with through the authority's own tree strategy and its highway powers instead. That does not make them easier to remove. Authorities are acutely aware of how contentious street tree felling has become, and many now publish a policy requiring consultation before any mature tree comes out.

The adjoining owner has no right to prune or fell a highway tree, including branches overhanging their boundary. Doing so anyway brings the same category of exposure discussed in the penalties for damaging a protected tree, with the highway authority as claimant rather than the planning authority.

Root protection areas and where a trench can go

BS 5837:2012 gives the method for calculating a root protection area from stem diameter, with the resulting radius capped for very large trees. That circle, adjusted for known root distribution, is the zone within which excavation is presumed to be damaging.

The utility industry works to its own guidance on installing apparatus near trees, which sets out precautionary distances and acceptable methods within them. The hierarchy is straightforward:

• Outside the root protection area, conventional open-cut trenching is normally acceptable.
• Within it, trenchless methods such as directional drilling or impact moling at an appropriate depth avoid the rooting zone altogether.
• Where excavation inside the zone is unavoidable, hand digging or air spade excavation exposes roots so they can be worked around rather than severed.
• Roots above a defined diameter should be retained and bridged, not cut.

Getting this into the design early costs far less than arguing it on site. A tree survey to BS 5837 covering trees outside the site that could be affected, not just those within it, gives you the root protection areas as a drawn constraint at the point the service corridors are being set out.

Illustrative example: a 16-unit scheme with a new access off a residential street lined with semi-mature limes. The drainage connection was drawn on the shortest route, straight through two root protection areas. Rerouting it 12 metres along the carriageway centre line, outside the zones, added a modest length of pipe and removed a consultation objection and a probable refusal reason. That example is illustrative.

Street works, notices and licences

Opening the highway is regulated separately from planning. A statutory undertaker works under the New Roads and Street Works Act 1991 notice regime, giving the street authority notice of the proposed works and allowing it to impose requirements. A developer laying private apparatus needs a licence under section 50 of the same Act.

Either way the street authority can attach conditions dealing with trees, and its arboricultural officer will often be consulted. Where the works are part of a wider highway scheme, the tree requirements will also appear in a construction traffic management plan alongside the routing and wheel-washing conditions.

Coordination between undertakers matters more than most developers expect. Four separate connections dug at four separate times, each nibbling at the same root plate, will kill a tree that would have survived one carefully planned trench.

Section 38 and section 278 agreements

Where new streets are to be adopted, the section 38 agreement sets the specification. Where works are carried out to the existing highway, the section 278 agreement does the same. Trees appear in both, and the terms vary enormously between authorities.

Ask three questions before the layout is fixed. Will the authority adopt trees in the carriageway or verge at all. What planting specification does it require, including soil volume, rooting medium, irrigation and guarding. And what commuted sum does it charge for maintenance, and over what period.

Some authorities decline to adopt street trees entirely, which pushes the planting into private land or a management company, and that changes the landscape strategy and the estate charge model. Finding that out at the discharge of conditions stage is expensive.

Removal, and what replaces it

Where an access cannot in practice be located elsewhere, most authorities will consider removal at the developer's cost. The usual package is replacement planting at a stated ratio, a commuted sum, and a period of aftercare.

Do not assume it. Mature street trees on a protected verge, or trees forming part of an avenue, are frequently refused, and the access has to move. Test this at pre-application, with a drawing showing the alternatives you considered, before the layout hardens.

Replacement planting also has to work. A whip in a 600 millimetre pit under a footway will not become a street tree. Rooting volume, soil specification, structural cells or raft systems under paving, and a watering regime for the establishment period all belong in the specification, and the highway authority will usually insist on them as the price of adoption.

Protection during the works

The protection measures are the familiar ones from BS 5837, applied in a setting where the contractor has less room and more traffic. Protective fencing to the root protection area, ground protection where fencing is impossible, no storage of materials or spoil within the zone, no mixing of concrete or washing out near roots, and no fixings into trunks.

An arboricultural method statement with a supervision schedule, secured by condition, is the mechanism that makes those measures stick. Name the trigger points at which the site arboriculturist attends, and record each visit.

One further point on sequencing. Clearing or grubbing ahead of a decision is a serious risk, and the same logic applies to the highway frontage, as set out in clearing a site before the application goes in. A damaged street tree before determination will colour every consultation response that follows.

This is general guidance, not 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.