Planning a Building Project Near Trees: What You Need to Know Before You Apply

BS 5837:2012 Trees in relation to design, demolition and construction, Recommendations is the standard planning authorities apply when a development sits near a tree. It governs which trees must be surveyed, how much ground around each must be kept clear, and what documents accompany the application.

The critical figure is the root protection area. For a single-stemmed tree it is the area of a circle whose radius is twelve times the stem diameter, measured at 1.5m above ground level, capped at 707m². A tree with a 400mm stem generates a protection radius of 4.8m in every direction.

That circle, not the canopy, is what constrains a design.

When a tree survey is required

A survey is expected where any tree could be affected by the proposed works, and the threshold catches more applications than most homeowners expect.

Trees within influencing distance of the development, broadly, within roughly their own height of the works, normally trigger the requirement. So do trees whose root protection area overlaps the construction footprint, access route, or material storage area, even where the tree itself is some distance away.

Three categories of tree are caught that applicants routinely overlook.

Trees on neighbouring land. BS 5837 applies to any tree that could be affected, regardless of ownership. A neighbour's beech overhanging the site constrains the design in exactly the same way as one on the applicant's own plot.

Street trees. Trees in the highway verge outside the property are caught where access works, service runs or scaffolding fall within their protection area.

Trees to be removed. A tree scheduled for felling as part of the scheme still requires survey and categorisation, because the authority is deciding whether the loss is acceptable.

Winchester makes the requirement close to universal on city applications. The district's TPO density and extensive conservation area coverage mean most mature trees in the urban area carry some form of protection already, and an application that ignores a protected tree will be invalidated rather than refused.

The four categories and what they mean for your design

A BS 5837 survey records each tree's species, dimensions, condition and estimated remaining contribution, then assigns a category. The category determines how hard the authority will defend the tree.

• Category A, high quality, with an estimated remaining contribution of at least 40 years. Removal is very difficult to justify and the design is expected to work around it.
• Category B, moderate quality, at least 20 years' remaining contribution. Retention is expected but removal can be justified against a strong case.
• Category C, low quality, at least 10 years. Removal is normally acceptable, though replacement planting may be conditioned.
• Category U, unsuitable for retention, typically because of irreversible structural defect or advanced decline. Removal is expected regardless of the development.

Category U is worth understanding before designing around a tree. A tree in advanced decline may be removable on its own merits, and establishing that at the feasibility stage can free a plot layout that would otherwise be built around a tree with five years left in it.

Categorisation is a judgement made by a qualified arboriculturist against defined criteria, not a negotiation with the applicant.

The four documents, and the stage each belongs to

A full application near trees typically requires four separate outputs, produced in sequence. Submitting them in the wrong order is the usual cause of delay.

1. Tree survey. The base data, every relevant tree recorded, measured, categorised. Produced before the design.

2. Tree Constraints Plan. The survey translated into a drawing showing each tree's root protection area and shade footprint on the site plan. This is a design input, not a submission document, and its whole purpose is to be produced early enough to change the layout.

3. Arboricultural Impact Assessment. An evaluation of the proposed design against the constraints, which trees are lost, which are affected, what the consequences are, and what mitigation applies. Submitted with the application.

4. Arboricultural Method Statement and Tree Protection Plan. The detail of how retained trees will be protected during construction: fencing positions and specification, no-dig construction where surfacing falls inside a protection area, service routing, and supervision points. Frequently conditioned rather than submitted, meaning the condition must be discharged before work starts.

Producing the Tree Constraints Plan after the architect has finalised the layout is the sequencing error that costs the most. The plan exists to shape the design, and applicants who commission it last discover the constraint at the point it is most expensive to accommodate.

Root protection during construction

Protection is a physical exclusion zone, not an instruction to be careful.

Fencing to the BS 5837 specification, a scaffold framework with welded mesh panels, not a line of plastic netting, is erected on the protection area boundary before any material arrives on site. Nothing enters: no excavation, no vehicle movement, no material storage, no cement washout, no site hut, no spoil heap.

Compaction is the damage mechanism applicants underestimate. Repeated vehicle passes over a root plate collapse the soil pore structure and asphyxiate roots without any visible injury. The tree declines two or three seasons later, long after the certificate of completion.

Where hard surfacing must fall inside a protection area, no-dig construction using a cellular confinement system laid over the existing grade is the accepted solution. It builds up rather than digging down.

Damaging protected roots is the same offence as felling

Severing the roots of a protected tree during construction is an offence under the Town and Country Planning Act 1990 in the same terms as cutting the tree down.

Two features of the offence catch developers. The tree does not have to die, wilful damage completes it. And an excavator operator acting within a general instruction to dig a trench does not insulate the person who gave the instruction.

Penalties reach £20,000 in the magistrates' court, and the authority can additionally require replacement planting. Where the damage becomes apparent only after the tree declines, enforcement can follow years after the building work.

Establishing whether a tree on or near the site is covered by a Tree Preservation Order is therefore a pre-design check rather than a pre-start one. Where the site falls inside a conservation boundary instead, the six-week notification route for conservation area trees applies to any tree work the scheme requires, and that six weeks runs concurrently with nothing.

Which authority determines your application

Part of Winchester district falls inside the South Downs National Park, where the National Park Authority is the local planning authority rather than the city council.

The distinction affects more than the address on the envelope. The Authority applies National Park policy to tree and landscape matters, its expectations on retention are generally more demanding, and its tree officers are separate from Winchester City Council's team. Confirming which authority determines the application before commissioning any survey work avoids producing a report to the wrong policy framework.

Winchester City Council's tree team is reachable on 01962 848 301 for properties in the city council's area.

The sequence that avoids the expensive version

1. Check protection status on every tree on and adjacent to the site, and confirm the determining authority.
2. Commission the tree survey before the architect draws anything.
3. Get the Tree Constraints Plan onto the site plan as a design input.
4. Design to the constraints, moving the building rather than the tree wherever the categories make that the cheaper outcome.
5. Submit the impact assessment with the application.
6. Erect protective fencing before the first delivery.

Schemes with a tree constraint run more cheaply when the survey comes first and the fencing goes up before the groundworks start, our work with property developers across Hampshire covers the implementation side, from protective fencing to supervised excavation within protection areas. Where a Category U or C tree genuinely does need to come out to make a scheme work, removal of a large tree on a constrained site is far simpler carried out before construction starts than negotiated once fencing, foundations and access routes are already in place.