A tree survey for a mortgage is a risk assessment an arboriculturist carries out when a lender is concerned that a large tree near the property could threaten the building — usually through subsidence on shrinkable clay soil — and it is a completely different document from the BS5837 survey used in planning. If your mortgage offer has come back conditional on a "tree report" or "arboricultural report", this page explains what the lender actually wants, why, and what happens next.
Why a lender asks for one
Mortgage lenders are protecting the value of their security — the house they are lending against. When a mortgage valuation or a fuller homebuyer/building survey spots a substantial tree close to the building, the surveyor may flag a potential subsidence risk and recommend the lender obtain specialist advice before releasing funds. The lender then makes the offer conditional on an arboriculturist's report that either:
- confirms the tree is not a material threat to the foundations; or
- sets out a management plan — for example a crown reduction cycle, a monitoring regime, or root-barrier works — that keeps the risk acceptable.
It is not a sign the purchase is doomed. In the large majority of cases the report clears the tree or proposes a light-touch plan, and the mortgage proceeds. The lender simply wants the risk assessed by someone qualified rather than assumed away — and wants it in writing so its own valuer is covered.
What actually drives subsidence risk
Contrary to the instinct to fell anything tall near a house, tree-related subsidence risk depends on a combination of factors, not the tree in isolation. A competent survey weighs all of these together.
| Factor | Why it matters | Higher risk when... |
|---|---|---|
| Soil type | The single biggest driver | Firm, shrinkable clay that swells wet and shrinks dry |
| Tree species / water demand | High-demand species pull far more moisture | Oak, poplar, willow, elm, eucalyptus |
| Proximity | Roots must plausibly reach under the foundations | Tree within ~1× its mature height of the wall |
| Foundation depth & age | Shallow footings sit in the zone soil moves | Pre-1950 shallow-founded property on clay |
| Tree size & maturity | Bigger canopy, bigger water uptake | Large, vigorous, actively growing tree |
| History of movement | Past cracking signals live risk | Recorded or visible progressive cracking |
Soil is the big one. Shrinkable clay swells when wet and shrinks when dry; a thirsty tree drawing moisture out of clay through a dry summer can cause the ground — and the foundations resting on it — to move. Sand, gravel and chalk soils don't behave this way, and tree-driven subsidence risk on them is much lower. The British Geological Survey shrink-swell data and local geology tell an arboriculturist a great deal before they even look at the tree.
The output of a good survey is a reasoned judgement — risk ruled in or out on the evidence — not a reflex "cut it down".
Worked example: the oak on clay
Picture a 1930s semi in the London clay belt with a mature English oak about eight metres from the rear elevation. The oak is perhaps 18 metres tall, so it sits comfortably within one tree-height of the wall, and oak is one of the highest-water-demand species there is. The property has traditional shallow strip footings. On that combination — high-demand species, close proximity, shrinkable clay, shallow foundations — a surveyor will look hard, check for existing crack patterns, and may recommend a monitoring period or a phased crown-reduction programme rather than clearing the tree outright.
Now move the same oak onto free-draining sand and gravel, with a 1990s deep-founded house: the risk profile collapses, and the report will very likely clear it with no action. Same tree, opposite conclusion — which is exactly why the lender wants a survey and not a rule of thumb.
The counter-intuitive part: don't just fell it
Removing a mature tree can be worse than keeping it. On clay that a tree has kept dry for decades, sudden removal lets the soil rehydrate and swell — a phenomenon called heave — which can lift and crack foundations just as damaging as subsidence, sometimes years later. This is precisely why lenders want a survey, not a chainsaw. The right answer is sometimes retention with a management plan, sometimes a phased reduction that lets the ground adjust gradually, and only sometimes removal.
And you may not be free to remove the tree at all. If it carries a Tree Preservation Order or stands in a conservation area, felling or heavy pruning without written consent is a criminal offence — fines can reach £20,000 in the Magistrates' Court for destroying a protected tree, with an unlimited fine on indictment. So a TPO check is an essential early step for any buyer, and our guide on buying a house with a TPO covers what protection means for you as owner.
How it differs from a planning tree survey
Buyers and even some agents conflate these, so it's worth being precise. They are different reports, for different jobs, read by different people.
| Mortgage / pre-purchase tree survey | BS5837 planning survey | |
|---|---|---|
| Purpose | Assess whether a tree threatens an existing building | Assess trees so a development can be designed around them |
| Trigger | A lender or homebuyer survey flags a nearby tree | A planning application affecting trees |
| Focus | Subsidence, heave, structural proximity, soil moisture | Retention value, categories A–U, root protection areas, construction impact |
| Standard | Building-damage / risk assessment convention | BS5837:2012 (a British Standard — guidance, not law) |
| Output | Risk assessment plus management recommendation | A tree schedule and usually an impact assessment |
| Read by | Your mortgage lender and its valuer | The council's tree officer |
If you're the one building rather than buying — an extension near a tree, say — you want the planning route instead: start with do I need a tree survey for planning. If your concern is purely a tree's physical safety (a suspect limb, storm damage), that's a tree risk assessment. And if you want to understand the vocabulary lenders and surveyors use, tree survey vs arboricultural survey untangles the overlapping terms.
Where insurers fit in
Subsidence is an insured peril, so the story doesn't end with the mortgage. If a property has a claims history, the buildings insurance may carry an exclusion or a higher excess for subsidence, which can itself affect the mortgage. Where there is a live or recent claim, insurers often prefer a monitored, engineered solution — root barriers, managed reductions, level and crack monitoring — over felling, for the same heave reasons an arboriculturist would cite. Our guide on trees, subsidence and insurers explains how the insurance and arboricultural pictures interact, which matters if you are buying a house that has moved before.
What to do if you're buying
- Read the survey flag carefully. Note exactly which tree the surveyor meant and precisely what worried them — proximity, species, existing cracking, or just caution.
- Check protection status with a TPO check before assuming anything can be removed or pruned.
- Instruct a suitably qualified arboriculturist — ideally an Arboricultural Association Registered Consultant or an ICF Chartered Arboriculturist, whose report a lender is far more likely to accept without quibble. See find a tree surveyor.
- Share the lender's exact wording with the arboriculturist so the report answers the question the lender is actually asking, not a generic one.
- Factor in the soil. If you don't know whether the ground is shrinkable clay, the surveyor can advise from local geology — it changes the whole assessment.
- Budget realistically. A focused pre-purchase or mortgage tree report is typically a few hundred pounds; a monitoring programme or engineered mitigation costs more but is usually far cheaper than an unnecessary felling and its consequences.
Requirements and records are set locally — check your area
There is no single national rulebook for how a tree near a house is treated. Two things that matter to a buyer are decided locally by the local planning authority (LPA):
- Protection status. Whether a tree carries a TPO, and whether the property sits in a conservation area, is set and recorded by the individual council — and TPO density varies enormously between authorities. A tree that is freely removable in one borough may be legally protected a mile away in the next.
- Any planning conditions on past works. Extensions and outbuildings near trees are often granted with tree-protection conditions; those live on the council's planning record for the property.
So a buyer must check the specific authority covering the address, not rely on a national assumption. PlanWatch tracks live planning activity and tree-related applications down to the individual council, so you can see the planning and tree history around an address before you commit. Explore example authorities such as Leeds, Manchester or Lambeth, or head to the tree-surveys hub to find yours. Note too that this guidance is England-centric: Scotland, Wales and Northern Ireland run parallel but distinct tree-protection regimes, so confirm the local rules if the property is outside England.
Used early, an arboricultural report is rarely a deal-breaker — it's the evidence that turns a vague survey worry into a clear, financeable answer.