The tree constraints plan and the layout it forces

A tree constraints plan layout conversation should happen before the first house type is placed, and on most schemes it happens after. The plan is the stage in BS 5837:2012 that translates a tree survey into spatial limits on design, and it carries far more than the root protection areas that everybody remembers.

Root protection areas are the easy part. For a single stemmed tree the area is derived from a radius of twelve times the stem diameter, capped at 707 square metres, and it goes on the drawing as a circle or a polygon. What forces the layout is the rest of the plan: current and future crown spread, height, and the shade the tree casts across the plots you are trying to sell.

What a constraints plan shows beyond the root protection area

The constraints plan sits between the survey and the impact assessment. It takes the surveyed trees, with their categories under the standard's system of U, A, B and C, and plots what each one demands of the site.

Four layers matter. Root protection areas, adjusted in shape where the ground conditions or existing structures justify it. Existing crown spread, measured on four or eight radii rather than drawn as a circle. Likely future crown spread, because a semi-mature tree retained today will be wider in fifteen years. And shade, plotted as a pattern across the site rather than described in a paragraph.

Category U trees are those in such condition that they should be removed regardless of the development, and they are not a constraint. Category C trees are of low quality and should not dictate a layout. The plan exists to show which trees are worth designing around, so say so on the face of it rather than plotting every stem with equal weight.

Shade patterns and their effect on room layouts

Shade is the layer that changes house positions. Plotting the shadow cast by retained trees at the equinox, with midsummer and midwinter comparisons, shows which plots receive morning light, which receive afternoon light and which receive very little of either.

Two design consequences follow. Rooms that need light, principally living rooms and kitchens, should not sit on the shaded elevation of a plot beside a large retained tree. And the garden of that plot should not be the part of the site in permanent shadow, because that is the garden whose owner writes to the council in three years asking to fell.

The BRE guidance on site layout planning for daylight and sunlight deals with obstruction by trees as well as by buildings, and offers a rule of thumb about the angle a tree subtends from a window. Check the current edition for the figures. On a scheme where shade is the dominant issue, model it rather than relying on a rule of thumb.

Height and the relationship to garden depth

Height governs the perception of dominance, which is a different thing from actual daylight loss and often a stronger driver of complaints. A 20 metre oak on the southern boundary of a 9 metre garden dominates that garden whatever the calculations say.

A common design rule is to keep the distance between a mature tree and a dwelling at least equal to the tree's likely mature height. That is a starting point rather than a standard, and on constrained sites it is unachievable. Where it cannot be met, say what you have done instead: orientating the plot so the tree sits beyond the garden rather than within it, increasing garden depth on the affected plots, or placing parking, a bin store or open space between the tree and the house.

Foundation design is a separate constraint in shrinkable clay, where species water demand and distance drive depth, and the industry guidance used by warranty providers sets out the relationships. Get the structural engineer's view before the layout is fixed, because deep foundations close to a tree may be technically possible and arboriculturally unacceptable. The related question of damage claims from neighbouring trees is covered in our note on trees and subsidence claims.

Future pressure to fell and how it is assessed

This is the part of the standard that developers treat as soft and that councils treat as hard. A retained tree that makes the adjoining home dark, drops leaves into a gutter, sheds fruit onto a car and frightens the occupier in a storm will be the subject of an application to fell within a few years.

Officers assess that pressure by asking practical questions. How far is the tree from the nearest habitable room window. Which way does the garden face. Is the tree within a private garden or in open space. Who will own and maintain it. Is there room for the crown to grow without touching the building.

A layout that scores in the right hand column will be challenged, and the honest answer is usually to move the plot rather than to promise a management regime. Conditions requiring retention do not survive contact with a resident who wants light.

Designing space for the tree to grow

Retention has to include growing room. Plot the crown as it will be at maturity, not as it is today, and keep buildings, hard surfaces and services out of that envelope.

The same applies to new planting, which is where landscape proposals most often fail. A street tree specified at 16 to 18 centimetre girth needs rooting volume, an unobstructed soil profile and a position clear of underground services, and a tree pit detailed as an afterthought produces a dead tree in five years. Set the soil volumes and pit details out in the Landscape Strategy and coordinate them with the drainage and utility layouts early.

Where trees sit in or near the highway, the coordination problem is worse again, and our note on street trees and utility trenching covers it.

Where retention is not credible

Sometimes the answer is that a tree cannot stay. Saying so early, with reasons, is better than proposing a retention that the arboricultural officer will not believe and that the impact assessment cannot support.

Be specific about why. The root protection area covers the only viable access. The tree sits in the middle of the developable area and is category C. Retention would put three plots into permanent shade and create pressure to fell within five years. Then set out what replaces it: replacement planting at a stated ratio, larger stock sizes, and the contribution to biodiversity net gain.

A defensible loss is far easier to argue than an indefensible retention. Officers see the second constantly and discount it.

Using the plan at pre-application

Take the constraints plan to pre-application before you take a layout. Ask the arboricultural officer which trees they regard as constraints, whether they agree with the categories, and where they would accept loss. That conversation, held over a constraints plan rather than a masterplan, changes the scheme at low cost.

Then build the layout from the plan outwards, and record how it responded. The tree survey and arboricultural impact assessment that follows will be much shorter, because the impacts you are assessing are the ones you designed for. Protection through construction is a further stage again, set out in retaining a tree through a construction programme.

Illustrative example. A 45 unit scheme retains a mature beech on the southern boundary. The first layout puts four rear gardens under its canopy. The constraints plan, plotted with equinox shade and mature crown spread, shows those gardens in shade for most of the afternoon. The layout is revised to place a parking court and an attenuation basin beneath the canopy, moving the four plots north. The arboricultural officer supports the scheme. The example is illustrative.

Enter your postcode on PlanScope to see which tree and landscape documents a scheme is likely to need. This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.