BS5837 grades every surveyed tree into one of four retention categories — A (high quality), B (moderate), C (low), and U (unsuitable for retention) — reflecting how valuable each tree is and how long it can be expected to contribute. The category drives which trees your development must be designed around, and it is one of the most contested lines in the whole survey.
Why trees are graded
The point of categorising trees is to tell a designer, a planner and a tree officer at a glance which trees are worth keeping. The higher the category, the more weight the tree carries in planning and the harder it is to justify removing. The grades feed straight into the arboricultural impact assessment that tests your layout — so understanding them tells you where your real constraints lie before you commit to a design. Categorising is a core output of any BS5837 tree survey, and it sits inside the wider set of five BS5837 outputs.
How the cascade works
BS5837 grades trees using a "cascade chart" (Table 1). A surveyor first weeds out the trees that can't be retained at all (U), then assesses the rest against arboricultural, landscape and cultural values, and finally sorts them into A, B or C by quality and expected remaining life. The expected-life thresholds are the backbone of the system: think of them as "how many more years is this tree realistically worth planning around?"
The four categories
| Category | Meaning | Expected remaining life | Plan colour (convention) |
|---|---|---|---|
| U | Unsuitable for retention — dead, dying, dangerous, or so structurally defective it can't reasonably be kept (loss expected within ~10 years). | Under ~10 years | Dark red |
| A | High quality — good examples well worth retaining. | 40+ years | Green |
| B | Moderate quality — retention desirable; may have remediable defects. | 20+ years | Blue |
| C | Low quality — unremarkable, or young/small; little constraint. | 10+ years (or young stems under 150 mm) | Grey |
Colours are the widely-used plan convention; BS5837 specifies precise spot-colours in its own tables, and some house styles vary (U is sometimes shown grey rather than dark red).
Category U — unsuitable for retention
These are trees that can't sensibly be kept — dead, dying, dangerous, or too structurally compromised to have a future. They are expected to be removed regardless of the development, so they place no meaningful constraint on your layout. But "U" is a retention judgement, not automatic permission to fell: if the tree has a Tree Preservation Order or sits in a conservation area, you still need consent or must serve a notice first. Even a genuinely dead tree usually requires five working days' prior notice to the LPA. The old "dead, dying or dangerous" exemption was narrowed by the 2012 Regulations to "dead" plus urgent works to remove danger — a trap for anyone quoting the outdated wording.
Category A — high quality
The best trees on the site — good specimens with 40+ years of expected useful life. These carry the most weight in planning. A scheme is expected to be designed around category A trees and their root protection areas, and removing one needs strong, evidenced justification that a tree officer will scrutinise closely. A veteran or ancient tree sits at the top of this scale and attracts enhanced protection under national policy.
Category B — moderate quality
Trees worth keeping, with 20+ years of expected contribution, possibly with defects that can be remedied by proportionate management. Retention is desirable, and category B trees still shape a good layout, but they carry less weight than category A if a genuine, unavoidable conflict arises. Much of a typical urban or suburban site falls into category B, so this is where most of the real negotiation with the tree officer happens.
Category C — low quality
Unremarkable trees, or young stems under 150 mm, with 10+ years of life. They impose little constraint and are the easiest to justify removing where the design needs it — though replacement planting is often expected as a condition, and a group of Cs can still matter collectively for screening or streetscape.
The subcategory numbers
After the letter comes a number showing why the tree has value:
- 1 = mainly arboricultural qualities (the tree itself is a good specimen — form, vigour, rarity).
- 2 = mainly landscape qualities (its contribution to the setting, screening, streetscape or skyline).
- 3 = mainly cultural values, including conservation, wildlife and historic interest.
So an A1 is a high-quality tree valued as a specimen, while a B2 is a moderate tree valued mostly for its landscape contribution. A single tree can carry more than one subcategory where it has value on several counts — for example a fine, prominent street tree that is also ecologically important.
Don't say "Category R"
A common error — repeated in older guides and 2005-edition references — is to talk about a "Category R" (remove) tree. In BS5837:2012 the correct code is "U" (unsuitable for retention). "R" is outdated; a current report should never use it. If you see "R" in a report, it's a sign the document is working from superseded wording, and worth questioning.
What your category means for building
- U: no constraint on layout — but check protection status before felling.
- A: design around it; removal needs strong, evidenced justification.
- B: retention expected where reasonable; a real factor in a good layout.
- C: low constraint; removable with justification, often with replacement planting.
Where categories trip applications up
Categories are one of the places applications most often go wrong. Optimistic grading — quietly marking a solid B tree as a C so it looks removable — is a favourite of weak reports, and an experienced tree officer will downgrade the design's assumptions right back, or reject the assessment outright. No grading at all is worse. The reverse also happens: a genuinely valuable tree understated to smooth a layout, only for a neighbour or the officer to flag it. A credible, defensible categorisation from a qualified surveyor is what makes the rest of the arboricultural report stand up to scrutiny — which is why the accreditation of the person doing the grading matters (see how to find a tree surveyor).
Category expectations are read locally
How much weight a given category carries in practice is not uniform across the country. The categories themselves are national — set by BS5837 — but how strictly a tree officer defends a B tree, how much replacement planting a C removal triggers, and how much conservation-area or TPO cover overlays the grading all vary by Local Planning Authority. An A tree in a borough with dense conservation-area coverage is far harder to touch than the same grade in an area with little tree cover and pressure to build.
Because that local reading is what actually decides your scheme, it pays to check your own council. PlanWatch tracks live tree-related planning activity per authority, so you can see how applications involving graded trees are handled where you are — compare, for example, Lambeth, Leeds and Bristol, then find your own area from the tree surveys hub.
Ready to get your trees graded? See our cost guide for likely fees, or use our directory to find a tree surveyor.
This guide covers England and the UK-wide BS5837:2012 standard. Statutory tree protection differs in Scotland, Wales and Northern Ireland — check local rules before any works.