Once you have your BS5837 tree constraints plan/survey, the next step is to use that information to steer the site layout. BS5837 is clear that trees are one of several design factors, but important trees can heavily influence what is realistically developable.
Reading the Constraints on the Layout Plan
Your designer now works directly over the tree constraints plan. Key constraints include:
- Root Protection Areas (RPAs) for all A, B and C category trees plotted on the plan as circles or polygons.
- Above‑ground considerations like canopy spread, height, shade, species characteristics and likely future size.
- Legal and practical issues: TPOs, conservation areas, existing services, access routes and sight lines.
The aim is to test options so that the best trees are retained with realistic space for growth and maintenance.
Designing Around Existing Trees
BS5837 says the default is that structures should sit outside the RPA of trees to be retained. Where that isn’t possible, any encroachment must be justified and supported by technical design.
When shaping the layout, the design team should consider:
- Daylight and sunlight – avoiding unreasonable obstruction, but also using shade where useful.
- Privacy and screening – trees can shield neighbouring properties or busy roads if building orientation and openings are planned around them.
- Direct damage risks – future root and stem growth, and branches rubbing on walls or roofs.
- Future pressure for removal – leaving enough space so occupiers don’t later demand that trees are felled.
- Seasonal nuisance – gutters, paths and parking layouts that can cope with leaves, fruit and honeydew.
Large mature or veteran trees need particular care: if you enclose them within development, you must allow generous long‑term space and realistic access for management.
When Layout Enters the RPA
If the only workable layout requires building within an RPA, BS5837 allows this only where you can show the tree will remain viable. In these cases, the project arboriculturist should:
- Demonstrate that any encroached area can be compensated elsewhere contiguous with the RPA.
- Propose mitigation measures to improve the soil environment, such as decompaction and mulching.
Foundation and surfacing design may then call on “special engineering” solutions like piles and suspended slabs, or no‑dig surfacing systems, all coordinated with arboricultural advice.
What Is an Arboricultural Impact Assessment (AIA)?
Once the layout is at a sensible draft stage, the arboriculturist prepares an Arboricultural Impact Assessment. This document evaluates the direct and indirect effects of the proposed design on trees – and of trees on the development.
The AIA should:
- Use the tree survey and constraints information as its base.
- Identify trees to be retained, removed and pruned, with clear numbering and plan symbols.
- Assess the impact of tree removals on amenity and character.
- Identify any potentially damaging activities near retained trees (demolition, new surfacing, excavation, service routes, level changes).
- Consider buildability: access for machinery, working space, materials storage and topsoil handling.
It should also flag which issues must be tackled in an Arboricultural Method Statement (AMS) and tree protection plan at the next stage.
What Goes Into the AIA Package for Planning?
For a typical planning application, BS5837 envisages the AIA as part of a small suite of documents. That package normally includes:
- Tree survey and constraints information.
- Finalised tree retention and removal plan.
- Proposed layout with retained trees and RPAs shown.
- Arboricultural Impact Assessment text and drawings.
- Draft tree protection plan and “heads of terms” for an Arboricultural Method Statement.
Putting this together at application stage shows the Local Planning Authority that the scheme is realistically buildable without unacceptable tree loss or damage.
