Turning a BS 5837 schedule into a tree constraints plan
The constraints plan sits between the survey schedule and the layout. Drawn before the houses, it saves a redesign; drawn after, it becomes an argument about felling.
A tree constraints plan drawing is the step between the tree survey schedule and the site layout, and it is the document an architect should have on the desk before the first house is drawn. It converts rows of measurements into areas on a plan that the design has to work around: the root protection area of each tree, its actual crown spread, its retention category and the shade it casts. Done properly it saves a redesign. Done as an afterthought once the layout is fixed, it becomes an argument about which trees can be felled.
The order is survey, constraints plan, layout. Not survey, layout, constraints plan.
What the constraints plan has to show
The British Standard on trees in relation to design, demolition and construction sets out what the survey records and what the constraints plan draws from it. The plan is a scaled drawing over an accurate topographic survey, and for every tree, group and hedge it shows:
- The tree reference number, matching the schedule exactly.
- The surveyed position of the stem, not the centre of the canopy.
- The actual crown spread, drawn from the measured radii rather than as a circle.
- The root protection area, plotted as an area with the correct size.
- The retention category, shown by the standard colour.
- An indication of the shade cast, where it affects the usability of proposed garden or amenity space.
It does not show the proposed development. That comes next, on a separate drawing, and keeping them apart is deliberate. The constraints plan is a statement of what exists. Once the layout is on it, people start negotiating with the constraints instead of designing to them.
Trees on adjoining land belong on the plan too, where their canopy or root protection area extends across the boundary. They are surveyed from within the site, with the limitation recorded in the report.
Plotting root protection areas accurately
The root protection area is calculated from the stem diameter, and the standard formula gives a radius of twelve times the diameter measured at 1.5 m above ground level, with the resulting area capped at the equivalent of a 15 m radius. For a multi-stemmed tree the calculation uses the combined stem diameters rather than the largest stem, which is the single most common arithmetic error in this field.
Three points of practice.
First, the root protection area is an area, not a circle. Where there is good reason to expect the roots to be distributed asymmetrically, because of a building, a road, a watercourse or a change in ground conditions, the shape may be modified. What may not change is the total area. An offset root protection area has to be drawn with the same number of square metres as the circle it replaces, and a plan that offsets without preserving the area will be queried.
Second, the reason for any modified shape has to be stated. "Offset to reflect the presence of the adjacent retaining wall" is a reason. A shape drawn to fit the plot layout is not.
Third, measure the stem diameter at the right height and on the right side of a slope. A tree on a bank measured from the downhill side gives a larger diameter and a larger root protection area, which sounds conservative until the discrepancy is spotted and the whole survey loses credibility.
Crown spread against canopy survey
Crown spread is recorded as four measurements, usually to the cardinal points, and the plan should join them into the actual outline of the canopy. Drawing a circle of the average radius is quicker and it misrepresents the tree.
It matters for two reasons. An asymmetric canopy is where shading and nuisance complaints come from, so the side with the long branches is the side where a window should not be. And branch spread, unlike the root protection area, is the dimension that governs clearance to a proposed building, because the crown will be pruned or the building moved, and the drawing has to show which.
Where the tree has a one-sided crown because it grew against a building that is being demolished, say so and note the likely response. A tree released from suppression on one side will grow into the space, which changes the clearance you need by the time the houses are occupied.
Colour conventions for retention categories
The standard assigns each retention category a colour so that a plan can be read at a glance, and consistency with it matters because officers and arboricultural consultees expect it.
| Category | What it means | Standard colour |
|---|---|---|
| U | Unsuitable for retention, in such condition that it cannot realistically be retained as a living tree in the context of the current land use for longer than ten years | Dark red |
| A | High quality, with an estimated remaining contribution of at least forty years | Light green |
| B | Moderate quality, with an estimated remaining contribution of at least twenty years | Mid blue |
| C | Low quality, with an estimated remaining contribution of at least ten years, or young trees with a stem diameter below the threshold | Grey |
Subcategories record why the tree has value: mainly arboricultural, mainly landscape, or mainly cultural including conservation value. A category B2 tree is retained for what it does to the setting rather than for its own quality, which changes how it should be treated in the layout.
Two cautions on category U. Its presence does not justify development, and a plan with a convenient cluster of dark red trees along the only developable frontage will be checked. And a U tree may still have ecological value, so a bat or bird assessment may be needed before it comes down whatever the arboricultural category says.
Shade patterns and future growth
Shade is the constraint most often left off, and the one that produces the most complaints from occupiers. An indication of the shadow cast by retained trees, commonly plotted around the spring equinox at three times of day, shows where a garden will be in shade for most of the growing season and where a ground floor window will receive little light.
The point is not to avoid all shade. Trees cast shade and that is part of why people value them. The point is to avoid putting a small north-facing garden under the crown of a mature oak and then receiving a request to fell it within two years of occupation.
Future growth works the same way. The survey records the tree as it is. The design has to accommodate it as it will be across the design life of the buildings, which means allowing for crown expansion and for the increase in stem diameter that enlarges the root protection area. A clearance that works on the day of the survey and not in fifteen years is a future pressure to fell.
Note: ground conditions matter as much as geometry on shrinkable clay, where the relationship between tree water demand and foundation depth is a structural question rather than an arboricultural one.
Overlaying the proposed layout
Once the layout exists, the constraints plan becomes the base for two further drawings. The tree protection plan shows the retained trees, the protective barriers and ground protection, the construction exclusion zones and any special engineering within a root protection area. The impact assessment reports the losses, the effect on retained trees and the mitigation.
The tests the layout has to pass:
- No part of a building footprint, including foundations and services, inside a root protection area without a specific engineered solution and a stated justification.
- Adequate clearance from crowns to windows and roofs, allowing for growth.
- No level change within a root protection area, including the build-up of a driveway, without a no-dig specification.
- Service runs, including drainage and incoming utilities, routed outside root protection areas, which is where most layouts fail at technical approval.
- Space for the protective fencing to stand where it needs to stand, which has to be accessible and workable during construction.
- Replacement planting with enough soil volume to reach maturity, which usually means more space than the drawing first allocates.
An Arboricultural Impact Assessment carries the reasoning, and councils expect a suitably qualified arboriculturist as the author with professional review strongly advised. Protective measures and site logistics belong in the Construction Management Plan, and the planting that replaces losses belongs in the Landscape Strategy with soil volumes and a management regime.
Mistakes that invalidate the plan
The ones that come back from consultation most often:
Root protection areas plotted as circles where the underlying survey already shows a wall or road that makes the circle impossible. Multi-stem trees calculated from the largest stem. Stem positions taken from a topographic survey that recorded canopy centres. Off-site trees omitted, so their root protection areas appear on the layout for the first time at technical approval.
Then the administrative ones. A plan with no reference to Tree Preservation Order or conservation area status, when those regimes apply regardless of the survey. Reference numbers that do not match the schedule. A drawing with no scale bar, no north point and no revision date. And a plan drawn on a topographic survey several years old, where the trees have grown and two have gone.
A final one that is easy to miss: hedges recorded as a single group with one root protection area, where the hedge contains individual trees that need their own. Where that hedge is also subject to the countryside hedgerow rules, two separate regimes apply to the same feature.
If you review arboricultural work for applicants, the professional directory is the route by which review requests reach a named reviewer for sign-off.
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.
Frequently asked questions
How is a root protection area calculated?
The radius is twelve times the stem diameter measured at 1.5 m above ground, and the resulting area is capped at the equivalent of a 15 m radius. For a multi-stemmed tree the calculation uses the combined stem diameters rather than the largest stem, which is the most common arithmetic error in tree surveys.
Can a root protection area be an offset shape rather than a circle?
Yes, where there is good reason to expect roots to be distributed asymmetrically because of a wall, road, watercourse or change in ground conditions. The total area must stay the same as the circle it replaces, and the reason for the modified shape has to be stated. Reshaping to suit a layout is not a reason.
What colours do the retention categories use?
Category U is dark red, A is light green, B is mid blue and C is grey. Officers and arboricultural consultees expect those conventions, so departing from them makes a plan harder to read and invites queries. Subcategory numbers record whether the value is arboricultural, landscape or cultural.
Do trees on neighbouring land go on the plan?
Yes, where their canopy or root protection area extends across the boundary. They are surveyed from within the site and the limitation on access is recorded in the report. Omitting them is a common failing, and their root protection areas then appear on the layout for the first time at technical approval.
Should the constraints plan show the proposed development?
No. Keep it as a statement of what exists, then overlay the layout on a separate tree protection plan. Combining them encourages the design team to negotiate with the constraints rather than design to them, and it makes the drawing harder for a consultee to check against the survey schedule.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.