Budgeting an arboricultural package stage by stage

An arboricultural package cost is not one fee. It is four separate commissions that fall at four different points in a project, and the sequence in BS 5837:2012 is what drives the order: a tree survey with a tree constraints plan before the layout, an arboricultural impact assessment once a layout exists, a method statement and tree protection plan after consent, and site supervision during construction. Pay for them in that order and each one informs the next. Pay for them out of order and you buy the first two twice.

The whole sequence on a single-plot site is modest. On a wooded site with a complex layout it becomes one of the larger consultant lines, and the biggest saving available is almost always a layout change rather than a cheaper consultant.

The documents in sequence and what triggers each

Four stages, four triggers, and the triggers are worth knowing because councils and conditions refer to them by name.

The tree survey and tree constraints plan are triggered by the presence of trees on or adjacent to the site. They come before design, and they are the reason a layout works or does not.

The arboricultural impact assessment is triggered by having a layout to assess. It cannot be written before the design exists, which is why a council asking for one at validation means the design is fixed.

The method statement and tree protection plan are usually triggered by a planning condition requiring their approval before work starts. Occasionally a council asks for them with the application on a sensitive site.

Site supervision is triggered by a condition requiring an arboriculturist to monitor specified operations and to certify completion. That is a cost line in the construction budget rather than the design budget, and it is the one most often forgotten.

The survey and constraints plan

The survey records each tree with a reference number, species, height, stem diameter at 1.5 m, crown spread, age class, condition, estimated remaining contribution and a retention category, and it produces a root protection area for each tree. The constraints plan draws those areas, the crown spreads and any shade patterns onto the topographical survey.

Scope it properly. The survey has to include trees on adjoining land whose canopy or root protection area extends into the site, and those trees are frequently the controlling constraint. Ask for the output as a DWG layer that overlays the tree survey data onto the levels survey, since a PDF constraints plan cannot be designed against.

Two cost drivers: the number of trees, and access. A survey of a hedgerow treated as individual trees costs far more than one treating it as a group, and an arboriculturist who cannot reach the base of a tree cannot measure its stem.

Commission this before the architect starts. A constraints plan delivered after the first layout means the layout changes, and redrawing a layout costs more than the survey did.

Impact assessment once a layout exists

The impact assessment takes the proposed layout and reports the effect on each tree: which trees are removed, which are retained, what encroachment into each root protection area is proposed, what the shade and future pressure position looks like, and what mitigation and replacement planting is proposed.

This is where a careful arboriculturist earns their fee by negotiating with the design rather than reporting on it. Moving a building line 600 mm, changing a drive from bound to no-dig construction or relocating a drainage run can turn an unacceptable encroachment into an acceptable one. An assessment written after the drawings are issued for planning can only describe the problem.

Replacement planting is part of this stage. Councils expect a planting schedule with species, sizes, numbers and locations, and a scheme that removes four mature trees and proposes four whips in the same positions will be challenged. Where the council has a canopy cover policy or a tree replacement standard, the ratio is set locally.

Expect the assessment to be a meaningful document rather than a form. Councils refuse schemes for inadequate tree information more often than for tree loss.

Method statement and tree protection plan after consent

The method statement specifies how the works inside and adjacent to root protection areas will be carried out: the protective fencing specification and its position, ground protection where access is needed, hand digging or air spade excavation near roots, the maximum root diameter that may be severed and who authorises more, the sequence of operations, the materials storage and mixing areas, and the supervision and certification points.

The tree protection plan is the drawing that goes with it, showing fence lines, ground protection extents, access routes, service runs and the construction exclusion zone.

Both are usually required by condition before development begins, which puts them on the critical path. Budget for the discharge application fee as well as the consultant fee, and build the authority's determination period into the programme. Grouping tree conditions with other pre-commencement conditions into a single discharge submission saves a fee, and the process is the one described in construction management plan conditions and their cost.

Site supervision as a conditioned cost

Supervision conditions specify attendance at defined stages: installation of protective fencing, any excavation within a root protection area, installation of no-dig surfacing, and removal of protection at completion. Each attendance is a half day or a day with a site visit report.

On a scheme with six retained trees and a no-dig drive, that can mean five or six visits across a build programme. Price it from the condition wording rather than guessing, and ask the arboriculturist for a schedule of attendances against the construction programme.

Two practical points. Supervision visits need booking against the contractor's programme, and a contractor who excavates before the arboriculturist attends has breached the condition, which is a problem for the client rather than for the contractor. And the certification at the end is what a purchaser's solicitor will ask for on sale, so keep the reports.

Where a layout change saves more than it costs

Illustrative example. A self-build plot has a mature oak with a stem diameter of 780 mm near the southern boundary, giving a root protection area radius of about 9.4 m. The first layout puts the house 7 m from the stem with a bound gravel drive crossing the area. The arboricultural advice is that the scheme needs a method statement, no-dig construction across the drive, hand dug foundations on the southern elevation and supervision at four stages.

Rotating the house 15 degrees and moving it 2 m north takes the foundations outside the area entirely. The drive still crosses it and still needs no-dig construction, and the supervision schedule drops to two visits. The design change costs a day of the architect's time and removes a larger sum from the construction budget, plus the risk premium a contractor prices into hand digging near a protected tree.

That trade is available on most sites and it is only available before the layout is fixed, which is the argument for commissioning the survey first.

Budgeting the whole sequence

Build the budget as four lines with their timing, not one lump.

1. Survey and constraints plan, at feasibility, scoped by tree numbers and including adjoining trees.
2. Impact assessment, at the point the layout is settled, with an allowance for one round of design iteration.
3. Method statement and protection plan, after consent, plus the condition discharge fee.
4. Supervision, in the construction budget, priced from the condition wording as a schedule of attendances.

Add two contingencies. One for a second survey where the first was carried out outside the season for assessing condition in leaf, or where the site changes. And one for a tree the council asks to be retained that your layout assumed would be removed, which triggers a redesign and a revised assessment.

Where a Tree Preservation Order or a conservation area applies, factor in the separate application or notification for tree works, with its own timescales. A conservation area notification runs for six weeks before works may proceed, and that period sits on the programme whether or not anyone objects.

The other pre-application costs sequence alongside this, as set out in when planning costs fall due on a small housing scheme. If you are pricing the written documents at the same time, PlanScope pricing sets out what each tier covers, and the arboricultural work itself should come from a qualified arboriculturist.

This is general guidance, not legal advice. Arboricultural fees vary by site and consultant, so obtain quotes against a written scope. Arboricultural assessment and method statements should be prepared by a suitably qualified arboriculturist, and councils usually expect a named author with relevant professional membership.