The tree constraints plan in a BS 5837 survey

The tree constraints plan is the drawing that should exist before the layout does. It takes the survey schedule from a BS 5837:2012 tree survey and turns it into spatial information a designer can work with: root protection areas, crown spreads, shade patterns and a category for each tree. Produced at the right moment it shapes the building footprint. Produced after planning drawings are fixed, which is the common case, it becomes a record of the conflicts already designed in.

What the plan shows

A tree constraints plan is a scale drawing, normally at the same scale as the site survey, carrying four layers of information for every tree recorded.

The existing crown spread, plotted from the four cardinal point measurements rather than drawn as a circle. The root protection area, shown as a plotted area rather than a note. The category, usually by colour or hatch, with a legend. And shade, where trees sit in positions that affect the usable parts of the site.

It does not show the proposal. That is the point of it. The moment a building outline appears on the same drawing, the conversation shifts from what the constraints are to whether they can be accommodated, and those are different questions asked at different times.

Category grading and what each letter commits you to

BS 5837:2012 sorts trees into four categories based on quality and remaining contribution.

Subcategories record why a tree matters: mainly arboricultural value, mainly landscape value, or mainly cultural and conservation value including veteran status. A category B tree that screens a row of houses from the site is a different negotiation from a category B tree in the middle of a field.

Category U is worth checking rather than accepting. It is the category most open to optimistic grading, and a council tree officer who disagrees will say so at consultation.

Calculating and plotting root protection areas

For a single stem tree, the root protection area is calculated as a circle with a radius of twelve times the stem diameter measured at 1.5 m above ground, with the resulting area capped at 707 m², which corresponds to a radius of about 15 m. Multi-stem trees use a different derivation of the stem diameter, and the survey schedule should show which was applied.

The area is what matters, not the shape. Where existing site conditions make roots unlikely in one direction, a building, a road or a river, the area can be redistributed into ground where roots are more likely to be, provided the total area is maintained and the reasoning is stated. Redistribution has to be justified by evidence about the soil and the existing constraints rather than by the shape of the proposed building.

Two errors turn up repeatedly. Plotting the root protection area as a tidy circle when a wall or an adopted road already prevents root growth on one side, which understates the usable ground elsewhere. And quietly reducing the radius to fit a footprint, which a tree officer with a scale rule will find in a minute.

Plot the areas at survey stage and leave them alone. If the design needs them changed, that is a discussion with the arboriculturist, recorded in the Tree Survey documentation.

Shade, future growth and what a plan can hide

Shade is the constraint designers forget, and it is the one that produces complaints from occupiers rather than objections from officers.

A mature tree to the south of a proposed dwelling casts shade across the garden and the principal rooms for much of the day, and the pressure to fell or heavily reduce it arrives within a year or two of occupation. Plotting the shade pattern at survey stage lets the layout put the tree to the north of the garden instead, which costs nothing at that stage.

Future growth is the second hidden constraint. The survey records the tree as it is, and trees get bigger. A young category C tree with twenty years ahead of it will have a wider crown and a larger stem diameter, which means a larger root protection area, by the time the development is halfway through its life.

Where the plan omits shade and growth, it is doing half the job. Ask for both.

Using the plan to position a building

The sequence that works is simple and is followed less often than it should be. Survey first, constraints plan second, layout third.

With the plan in front of you, the moves available are clear. Shift the footprint out of the root protection area rather than proposing a no-dig construction to get into it. Route drainage and service runs outside the areas, because a single trench through a root protection area can do more damage than the building. Keep site access, compounds and material storage off the areas, which is a construction issue that has to be resolved at layout stage because there may be nowhere else to put them.

Where an incursion is unavoidable, the standard allows engineered solutions, cellular confinement systems, pile and beam foundations, no-dig surfacing, and the arboriculturist should be specifying them rather than the architect assuming them. These solutions have real cost, and the earlier they enter the appraisal the better.

The layout rationale belongs in the Design and Access Statement, and a design evolution section that shows the footprint moving because of a root protection area is exactly the kind of evidence officers respond to.

When the plan is drawn after the design

In practice many arboriculturists are appointed after the planning drawings are complete, and are asked to produce a constraints plan that supports a layout already fixed.

The honest response is to produce the plan properly and let it show the conflicts. Reports that quietly redraw root protection areas to fit the scheme damage the arboriculturist's position and rarely survive consultation. A tree officer reads dozens of these.

Where conflicts are found late, the options narrow to redesign, engineered solutions at cost, or an argument for removal with replacement planting. The last of these works better for category C trees than for category A, and not at all for a tree protected by a Tree Preservation Order unless the case is strong. Trees in a conservation area carry their own notification requirement before works, with a notice period the council can use to make an order.

Moving from constraints to impact assessment

The constraints plan feeds the arboricultural impact assessment, which identifies the trees affected, quantifies the loss, and proposes mitigation. That in turn feeds the tree protection plan and the arboricultural method statement, which are the documents the contractor works to.

Keep the tree numbers consistent through all four. Where the same trees appear in an ecological report or a Biodiversity Net Gain Assessment, the numbering should carry across, since hedgerows and individual trees are counted in the statutory metric and mismatched references make the calculation impossible to check.

The protection measures themselves land in the construction phase sections of a management plan, which is where fencing specifications, ground protection and supervision get written down for people on site.

Councils expect this work from a suitably qualified arboriculturist, and professional review is strongly advised before submission. Browse all 66 PlanScope report types to see which tree and landscape documents a scheme is likely to need.

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