BS5837:2012 tree surveys for development

BS5837:2012 — Trees in relation to design, demolition and construction exists to put tree information into a development process at the point where it can still change the design. Its underlying argument is simple: decide which trees are worth keeping before you fix the layout, not after.

The standard is guidance, not law. It acquires force through the planning system — most UK local planning authorities require an arboricultural assessment prepared to BS5837 as a validation requirement where trees are present, so in practice it is mandatory on any site with trees.

Every tree surveyed is assigned a category reflecting its quality and remaining contribution, which then drives how much weight it carries in design decisions:

• Category U — trees that cannot realistically be retained beyond the short term because of their condition. Assessed first, and removed from the constraints picture.
• Category A — high quality, with an estimated remaining life of at least 40 years. A material constraint; losing one usually needs strong justification.
• Category B — moderate quality, at least 20 years remaining. Retained where the layout reasonably allows.
• Category C — low quality, at least 10 years remaining, including young trees below 150mm stem diameter. Should not by itself constrain development.

Categories are further subdivided by the basis of value: subcategory 1 for arboricultural qualities, 2 for landscape qualities, 3 for cultural or conservation value. A U categorisation is a condition judgement and must be evidenced — it is the category most often challenged.

The root protection area is the notional area around a tree that must remain undisturbed for it to survive construction. For a single-stem tree the radius is the stem diameter at 1.5m multiplied by twelve, subject to a cap equivalent to a 15m radius. Multi-stem trees use the standard's combined-diameter method.

The resulting area can be reshaped where soil conditions, existing structures or known root distribution justify it — but the total area must be preserved. RPAs that have been quietly shrunk to fit a plot boundary are the most common reason an arboricultural report is rejected.

• Tree survey — the record of each tree: reference, species, height, stem diameter, crown spread, age class, condition, estimated remaining contribution, category and RPA.
• Tree constraints plan — the survey drawn spatially, showing RPAs and shade, produced before the layout is fixed.
• Arboricultural impact assessment — what the proposed design does to those trees: removals, incursions into RPAs, and their significance.
• Tree protection plan — the physical protection measures, fencing lines and construction exclusion zones.
• Arboricultural method statement — how any work inside an RPA will be carried out, usually with a schedule of supervision.

Where the sequence is followed properly, the constraints plan informs the layout. Where it is not, the impact assessment becomes a justification exercise for a layout already drawn — which is where objections arise.

A BS5837 survey is data-heavy: a dozen or more fields per tree, all of which must be internally consistent and spatially accurate enough to plot RPAs against a topographic survey. Recording on paper and transcribing later is where errors enter, and a transposed stem diameter changes an RPA by metres.

Capturing directly against a mapped asset, with the categories and dimension fields structured at the point of entry, removes the transcription step entirely. Arbrium's configurable survey templates support that approach; BS5837-specific templates are on the near-term roadmap for enterprise customers, alongside the general tree inspection and ash dieback survey types available today.

If you need a BS5837-based report for a lender rather than a planning authority, see our mortgage tree reports page.