Tree constraints plan against tree protection plan

A tree constraints plan and a tree protection plan are two different drawings, produced at two different stages, for two different audiences. The constraints plan tells the designer where the trees will not let them build. The protection plan tells the contractor what to fence off and when. Asking your arboriculturist for a tree constraints plan vs protection plan in the same breath, at the same moment, usually produces a hybrid that does neither job well.

Both come from BS 5837:2012, which sets out a sequence: survey the trees, plot the constraints, design, assess the impact, then plan the protection. Skip a step and the drawings stop agreeing with each other.

What each drawing is for

The tree constraints plan is a design tool. It takes the survey data and shows, on the topographical base, what each retained tree needs to survive the development and remain in acceptable condition. It is produced before there is a layout, and its whole purpose is to shape one.

The tree protection plan is a construction document. It assumes the design is fixed, shows which trees go and which stay, and sets out the physical measures that keep the retained trees safe during demolition and construction. It is usually the drawing referred to in a planning condition, and it is read on site by people who have never opened BS 5837.

Between the two sits the arboricultural impact assessment, which explains the losses, the incursions into root protection areas and the reasoning. The impact assessment is the narrative; the protection plan is the instruction.

When the constraints plan is produced

Straight after the survey, and before the architect draws anything. That is the sequence the standard intends and the one that saves money.

The survey itself records, for each tree, a reference number, species, height, stem diameter measured at 1.5 metres, branch spread at four cardinal points, crown clearance, age class, condition and estimated remaining contribution. Trees are then categorised: U for those that should be removed regardless, A for high quality specimens with a long remaining contribution, B for moderate quality, C for low quality or young stock.

The categorisation drives the design conversation. Losing a category C hawthorn to achieve a workable layout is an ordinary trade. Losing a category A oak is a reason to move the building.

Where a tree carries a preservation order or sits in a conservation area, the constraints plan should say so on its face, because the consent route changes. Getting this onto the drawing early also avoids the awkward discovery, halfway through a construction programme, that a tree everyone assumed was expendable is protected. The practicalities of holding a tree through the build are set out in retaining a tree through a construction programme.

Root protection areas and shade plots on the constraints plan

Two constraints are drawn, and they behave differently.

The root protection area is calculated from stem diameter: a radius of 12 times the stem diameter for a single-stemmed tree, with the resulting area capped at 707 m². It is drawn as a circle first, then adjusted in shape where soil conditions, existing structures or topography mean the roots cannot be where the circle says they are. The adjusted shape must keep the same area. An arboriculturist who simply deletes the part of the circle that falls under the proposed building has not done the adjustment; they have moved the constraint out of the way.

The shade plot is the second constraint, and it is the one designers ignore until the first complaint about a dark living room. It maps the shadow cast by retained trees across the site through the day and the year, and it exists so that habitable rooms and gardens are not placed where the tree will dominate them. A house sited in the permanent shade of a mature beech generates pressure to fell that beech within five years of occupation.

Draw both, in different line weights, over the topographical survey with levels. A constraints plan without levels is close to useless, because the relationship between existing ground, proposed ground and root depth is where most damage happens.

What the protection plan adds

Once the layout is fixed, the protection plan converts the constraints into instructions.

• Retained trees, trees to be removed and trees on adjoining land, each identified by survey reference.
• Construction exclusion zones, with the line of protective barriers plotted to scale.
• The barrier specification, which defaults to a scaffold framework with weldmesh panels unless a different specification is justified.
• Ground protection where working within a root protection area is unavoidable.
• Routes for services, with any hand-dug or trenchless sections identified.
• Areas for site huts, material storage, mixing and vehicle movement, all outside the exclusion zones.
• Any facilitative pruning needed to allow access or construction, specified properly rather than left to the operative.

Pruning is the item most often fudged. A note reading "prune as required" invites the contractor to reduce a crown by a third, and that is how a retained category A tree ends up as a category C one. Specification discipline is covered in writing pruning specifications properly.

The protection plan travels with an arboricultural method statement, which gives the sequence, the supervision regime and the trigger points at which the arboriculturist has to attend site.

Which drawing the validation list asks for

This varies by authority, and that variation is the source of a good deal of wasted effort.

Most local validation checklists ask for a tree survey and an impact assessment where trees are present on or adjacent to the site, and then secure the protection plan by condition. A few ask for the protection plan up front. Read the checklist rather than assuming, and where the requirement is ambiguous, submit the tree survey with the constraints plan and offer the protection plan by condition.

Keeping both current as the design changes

Designs move. Trees do not.

Every time the footprint shifts, the levels change or a drainage run is rerouted, both drawings need checking. The failure mode is familiar: a protection plan prepared against revision C of the site layout, submitted with revision F, showing a barrier line running through the middle of the approved building. Officers spot this, and it delays determination.

Build a check into the design programme at each issue. It takes an hour and it prevents the condition discharge being refused eighteen months later.

Levels changes deserve particular attention. Lowering ground within a root protection area severs roots even where no building is proposed, and a level change of 150 millimetres across a rooting zone can be more damaging than a foundation placed carefully at the edge.

Common drafting errors

The recurring ones, in rough order of frequency:

1. Root protection areas drawn as circles with the inconvenient segment deleted rather than the shape adjusted at constant area.
2. Trees on neighbouring land omitted, despite their root protection areas crossing the boundary.
3. No shade plot at all, or a shade plot for midsummer only.
4. Barrier lines shown as a dashed annotation rather than plotted to a dimension the site manager can set out.
5. Survey data more than a couple of years old presented as current.
6. Service routes shown on the engineer's drawing but not on the protection plan, so nobody notices the foul run crossing an exclusion zone.
7. Categories assigned generously to trees the design needs to remove.

The last of those is the one that damages credibility. A council tree officer reading a survey where every tree in the way is category C, and every tree at the site edge is category A, will treat the whole document with suspicion.

If you are assembling the evidence base for a site with trees on or beside it, the Landscape Strategy usually sits alongside the arboricultural documents, and the two should share the same retained tree schedule.

Enter your postcode on PlanScope to see which tree and landscape documents your site is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.