What if my neighbour's tree affects my plans?

Tree on neighbour's land but RPA crossing your boundary still requires AIA + foundation design accommodation. Neighbour permission not needed for design changes (you adjust your scheme). Cannot prune neighbour's tree without consent + cannot affect TPO/CA trees without notification.

How long is AIA valid?

Typically 12 months from survey date. If application takes longer to submit, fresh survey may be required (trees grow/decline). On long-running schemes, AIA refresh £350–£650.

Can I remove a tree to avoid AIA?

Only if no TPO + outside CA + no other protection. Felling TPO tree without consent: £20,000 court fine per tree + replacement order. Felling CA tree without 6-week notification: £2,500 fine + replacement. AIA cost (£450–£1,850) far cheaper than risk of unauthorised felling.

Arboricultural Impact Assessment London 2026 | Builderr

What Is an Arboricultural Impact Assessment for London Planning?

Arboricultural Impact Assessment (AIA) per BS 5837:2012 required when planning works within or near tree Root Protection Areas (RPA = 12× stem diameter). Survey + categorisation (A/B/C/U) + RPA mapping + impact assessment + mitigation. Cost £450–£1,850 by certified arborist. Foundation design within RPA may require cantilever raft, screw piles, or hand-dug pads with arborist supervision.

When AIA required

Required when: (1) any planning application includes works within 15m of TPO tree or significant CA tree; (2) extension/foundation excavation within Root Protection Area (RPA) of any tree on or adjacent to site; (3) tree removal proposed as part of works; (4) demolition affecting tree-lined boundaries. Local authority tree officer reviews AIA + comments on application. Many London boroughs (Richmond, Barnet, Bromley, Kingston, Sutton) have wide tree protection — most planning applications in these areas need AIA. Typical residential extension within 5–15m of mature tree: AIA almost certainly required.

BS 5837:2012 methodology

Tree survey: every tree within influencing distance recorded with species, height, crown spread, stem diameter at 1.5m, age class, physiological condition, structural condition, estimated remaining contribution. Categorisation: Category A (high quality, retention strongly desirable, RPA strict no-go); Category B (moderate quality, retention desirable, RPA design constraint); Category C (low quality, retention beneficial); Category U (unsafe/dying, removal recommended). Root Protection Area (RPA): plan area = 12× stem diameter (e.g. 600mm DBH tree = 7.2m radius RPA = 162m² no-build zone). Construction Exclusion Zone (CEZ) = RPA + protective fencing. Tree Protection Plan (TPP) shows RPAs + fencing + ground protection + service routes.

Foundation design within RPA

Standard strip/trench foundations within RPA prohibited (root damage). Solutions: (1) Cantilever raft — reinforced concrete raft spanning over RPA + supported on piles or pads outside RPA; £8,500–£18,500 premium vs standard strip. (2) Screw piles — steel piles screwed into ground with minimal root disturbance; £5,500–£12,500 premium. (3) Hand-dug pad foundations — bear on isolated pads outside major roots, dug by hand under arborist supervision; £3,500–£8,500 premium. (4) Stilted/suspended ground floor — building lifted clear of ground; minimal foundation footprint; £6,500–£15,500 premium. Builderr's Brent Queens Park + Haringey Muswell Hill case studies both used mini-pile foundations for TPO tree retention.