Budgeting a BS 5837 tree evidence base

Arboricultural work for a planning application comes in stages, and the tree survey cost planning teams budget for is usually only the first of four or five invoices. The sequence set out in the British Standard for trees in relation to design, demolition and construction runs survey, tree constraints plan, arboricultural impact assessment, tree protection plan and method statement, then site supervision. Each stage is priced separately, each depends on the one before, and the design has to pause between two of them.

The single biggest cost driver is not the number of trees. It is whether the survey was commissioned before or after the layout was drawn.

The survey, the constraints plan and the impact assessment

The survey records each tree with its species, height, stem diameter measured at 1.5 metres, branch spread at four points, crown clearance, age class, physiological and structural condition, an estimated remaining contribution in years, a quality category and preliminary management recommendations. From the stem diameter comes the root protection area, calculated as a circle of radius twelve times the stem diameter and capped at 707 square metres.

Categories run U, A, B and C. Category U trees are those that should be removed for sound arboricultural reasons regardless of any development. A, B and C run from high through moderate to low quality, with subcategories recording whether the value is arboricultural, landscape or cultural. Losing a category A tree is a serious planning problem. Losing a category C hedgerow sapling is not, and knowing which you have before you design saves months.

The tree constraints plan takes the survey and draws it: root protection areas, crown spreads, shade patterns, and the above-ground constraint of existing branches. It is a design tool, and it belongs on the architect's desk before the layout is fixed.

The arboricultural impact assessment comes after the design and reports what the proposal does to the trees. It cannot be written before there is a design, which is why sending an architect a survey and asking for "the tree report" produces confusion and an extra fee.

What each stage costs to produce

Nobody publishes a national tariff, and quotes vary by region and by practice, so get two. What moves the price is predictable:

• the number of trees, groups and hedgerows, and whether off-site trees have to be recorded from within the site
• whether a topographical survey already plots the trees, because an arborist who has to locate every stem is doing survey work twice
• access, especially where trees stand in neighbouring gardens and permission to enter is needed
• whether any tree needs a climbing inspection or decay detection, which is separate work
• whether the site is in a conservation area or carries a preservation order, which raises the level of detail councils expect

Ask for a fee proposal broken down by stage rather than a single figure. A practice that prices survey, constraints plan, impact assessment, protection plan, method statement and supervision separately is telling you how the work will run.

Root protection areas and design iteration

This is where the money is either saved or wasted.

A root protection area is not a no-build zone in every case. The standard allows encroachment where it can be justified and compensated elsewhere in the root protection area, and it allows special engineering such as no-dig cellular confinement construction for driveways and parking within it. What it does not allow is trenching for services straight through the middle of one.

The cost pattern is simple. One round of iteration between the constraints plan and the layout is normal and costs little. Three rounds, because the layout was drawn first and the trees were surveyed afterwards, is not. The arboriculturist re-runs the impact assessment each time, and on a scheme of any size that is a meaningful fee each round.

Service runs are the classic late discovery. Drainage, water, electricity and telecoms all have to get to the building, and routing them outside every root protection area on a treed site sometimes needs the drainage strategy and the arboricultural method statement to be developed together.

The method statement and the supervision stage

Where permission is granted, the conditions usually require a tree protection plan and an arboricultural method statement to be approved before work starts, and often require arboricultural supervision at defined stages.

The method statement is a practical document: the fencing specification and its position, ground protection where vehicles must cross a root protection area, the sequence of demolition and construction near trees, how any approved encroachment is carried out, and what happens if roots larger than a stated diameter are found.

Supervision is the line most first budgets miss. A named arboriculturist attends at stated hold points, signs off the fencing before demolition, witnesses excavation within root protection areas, and reports to the council. On a twelve month build that is several visits plus reporting, and the council will not discharge the condition without the records. Price it as a monthly retainer or a fixed number of visits at the outset.

Trees subject to a preservation order

A preservation order changes the process rather than the survey. Works to a protected tree need the council's consent, and the application is free. In a conservation area, works to trees above the stated size require six weeks' written notice to the council under section 211 of the Town and Country Planning Act 1990, during which it can make an order.

The budget effect is in time rather than in fees. A consent application has its own determination period, and a refusal has its own appeal route. Where a scheme depends on removing a protected tree, the case has to be made on arboricultural grounds with replacement planting proposed, and the tree survey evidence needs to be strong enough to carry it.

Where protected trees are removed without consent, the offence is prosecutable and the council can require replacement. That is not a budget line anybody plans for.

Costs where a survey is done twice

Four situations produce a repeat survey, and three of them are avoidable:

1. The survey is more than a year or two old at submission, and the validation officer asks for it to be updated. Councils differ on the acceptable age, so ask before commissioning.
2. Off-site trees whose root protection areas extend into the site were not recorded, usually because the surveyor was told to survey the site rather than the trees affecting it.
3. The layout changed after the impact assessment, so the assessment no longer describes the proposal.
4. A storm, disease or a neighbour's removal changed the baseline between survey and submission, which is the one you cannot prevent.

Number two is the most common and the most annoying, because it is fixed by one sentence in the brief.

Sequencing the work against the design programme

The order that works:

1. Commission the survey and the constraints plan at feasibility, before any layout is drawn.
2. Design against the constraints plan.
3. Commission the impact assessment once the layout is settled.
4. Prepare the protection plan and method statement for submission or for discharge of conditions.
5. Hold a supervision budget for the construction period.

Tree surveys can be done at any time of year, unlike ecology work, so there is no seasonal excuse for leaving it late. Condition assessment is easier in leaf, and a survey done in deep winter may carry caveats on crown condition, which is worth knowing if the scheme turns on whether a tree is category B or C.

Arboricultural work to the British Standard is expected from a suitably qualified author, and professional review of any draft is strongly advised. The same staged logic applies to other technical evidence bases, including budgeting a contaminated land investigation and budgeting an acoustic evidence base for a noisy site, where site work has to lead the design rather than follow it.

This is general guidance, not legal advice. Council requirements on survey age and supervision vary, so check the local validation list before commissioning.

See PlanScope pricing if you are working out where drafting the supporting statements fits against the specialist survey budget. Reports should be reviewed before submission, and we do not guarantee planning approval.