Tree and subsidence claims: the evidence a council needs

A letter from a loss adjuster saying the oak is causing the cracking will not get you consent to fell a protected tree. Councils that deal with subsidence claims regularly expect four things: proof that the building is founded in shrinkable clay, proof that roots of that species are present under the affected foundations, level monitoring through a full seasonal cycle showing movement in the expected pattern, and a reasoned explanation of why crown management or repair will not solve it. Miss any one of those and the tree officer has a straightforward refusal to write.

That is not obstruction. A Tree Preservation Order exists because the authority decided the tree had amenity value, and the 2012 Regulations require it to weigh the case for removal against that value on evidence.

Why a bare insurer's letter fails

Subsidence letters written for insurance purposes answer a different question from the one the tree officer is asking. The insurer wants to know whether the claim is covered and which repair route costs least. The authority wants to know whether this particular tree is the cause, and whether anything less than felling would work.

Three assertions appear in almost every weak application. That the tree is close to the property, which is not evidence of causation. That the species is high water demand, which tells you the risk is plausible and nothing more. That the insurer requires removal, which is a commercial position rather than an arboricultural conclusion. Officers see all three weekly.

Soil, foundations and the trial pit

Clay shrinkage subsidence needs a shrinkable soil. If the house sits on sand, gravel or chalk, vegetation-related shrinkage is off the table and the cracking has another cause, which is worth knowing before you spend anything else.

A trial pit adjacent to the affected corner of the building gives the whole foundation picture in one exercise. The report should record the depth and type of foundation, the soil profile by depth with a description of each stratum, the depth of desiccation if present, and samples taken for laboratory testing.

The laboratory work that carries weight is the plasticity test. A plasticity index in the intermediate, high or very high range supports a volume change case; a low index undermines it. Where the desiccation profile is measured, moisture content against depth compared with a control location away from the tree is more persuasive still, because it shows drying where you say the roots are drawing water.

Identifying the roots under the building

Root presence is where most applications fall apart. Fine roots turn up in trial pits everywhere, and on their own they prove very little. What matters is roots of a species consistent with the suspect tree, at or below foundation level, in the zone of desiccated soil.

Species identification is a laboratory exercise, usually by anatomical examination of a root sample. Send samples with a clear reference to the pit, the depth and the face they came from. Where several trees are candidates, and there usually are, identification to species narrows the field, and where two species are present you have to deal with both rather than pick the one your client wants gone.

A short point that saves arguments later. Record the distance from the trunk to the affected wall and the tree's height, because the ratio is the first thing a tree officer checks against the general pattern of influence for that species.

Level monitoring through a full seasonal cycle

Level monitoring is the evidence that distinguishes clay shrinkage from every other cause of cracking, and it cannot be rushed. Points are installed on the building, read to a fixed datum, and read again at intervals through the year.

What the authority is looking for is a seasonal signature. Downward movement through the summer as the soil dries, recovery through the autumn and winter as it rehydrates, and the largest movement nearest the tree. A pattern of steady one-directional movement through all seasons points somewhere else: leaking drains, historic settlement, made ground or a failed lintel.

Twelve months of readings at monthly intervals is the normal ask. A shorter run covering only the late summer months can support an urgent case, but expect the officer to grant consent for crown reduction rather than felling and to ask for the remaining readings. Include the raw readings and the datum details as well as a graph, and note any interruption in the record.

Crack monitoring with tell-tales or calipers is useful supporting material and is not a substitute. Cracks open for many reasons.

Options short of felling

The regulations require the authority to consider whether a lesser intervention would serve, so an application that has not addressed the alternatives is incomplete on its face.

• Cyclical crown reduction, specified properly, with a stated percentage and a return interval, which reduces water demand without losing the tree
• Root severance with a physical barrier installed in a trench between the tree and the building, where site conditions allow and the tree's stability is assessed first
• Repair of the damage combined with monitoring, where movement is small and the building is tolerant
• Underpinning or foundation strengthening, which is expensive and is often the honest answer where the tree has high amenity value and the damage is modest

Crown reduction is the option most often granted, and it is also the one most often badly specified. A consent that says reduce by 30 per cent is close to meaningless in practice, which is why the specification deserves the same care as any other schedule of works. Our note on writing pruning specifications properly covers the wording that survives being handed to a contractor.

Illustrative example: a mature lime 7m from the rear corner of a 1930s semi on London Clay, with monitoring showing 6mm of seasonal cyclical movement at the nearest point and 1mm at the far corner. A cyclical reduction on a three year cycle, with continued monitoring, is a proportionate outcome. The same monitoring showing 25mm of movement, cracking through the lintels and roots of lime confirmed at 1.2m depth under a 600mm foundation makes a different case.

Putting the application together

For a tree covered by a Tree Preservation Order, you are applying for consent for works under section 198 of the Town and Country Planning Act 1990 and the Town and Country Planning (Tree Preservation) (England) Regulations 2012. For a tree in a conservation area that is not the subject of an Order, you give the authority six weeks notice under section 211 instead, and the same evidence still decides the outcome.

Submit as one bundle: the structural engineer's report, the trial pit log and laboratory results, the root identification certificate, the level monitoring record with the datum and raw readings, an arboricultural report by a suitably qualified arboriculturist covering species, condition, amenity value and the options considered, a plan showing the tree, the building and the pit locations, and photographs of the damage with dates.

A tree survey prepared to BS 5837:2012 does a different job, and where the property is also being extended it is the document the planning case officer will want. If the works form part of a wider building project, the sequencing matters, and our guide to retaining a tree through a construction programme sets out how the two consents interact.

If consent is refused

The authority must give its reasons. Read them for what they attack: a refusal that turns on the absence of root identification is curable, while one that turns on the amenity value of a landmark tree in a conservation area needs a different approach.

There is a right of appeal to the Planning Inspectorate against refusal of consent for works to a tree covered by an Order, and the 2012 Regulations also contain a limited compensation route where loss or damage follows from a refusal, subject to exclusions and a claim period. Take advice on that before relying on it, because the exclusions do real work.

Where the neighbour's tree is the problem rather than your own, liability and cost recovery work differently, and the neighbouring property angle sets out who applies and who pays.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.

Browse the PlanScope report types to see what a tree-related application usually needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.