Subsidence – Risk, Response and Remedies
Philip Hill – Landmark
What Will We Cover
 What is subsidence and equally important what is not.
 The lender and insurer approach to subsidence including
general policy terms and exclusions, claims management
and recovery and contribution.
 Subsidence risk assessment methods.
 The range of actions the property owner can take to reduce
the risk of subsidence.
What is Subsidence?
‘Subsidence is the vertical downward movement of a building
foundation due to loss of support of the ground from volumetric
changes in sub soil’
There are a number of visible indications:
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Vertical/diagonal cracking – tapered in width.
Cracks through Damp Proof Course (DPC)
External cracking reflected internally
Rucking of wallpaper at corners
Re-pointing of mortar joints diagonally or
vertically up walls
Distortions of openings – doors/windows stick
Rotation of the building towards trees on
shrinkable clay soils
Cracks appearing after a prolonged period of
dry weather
Seasonal opening and closing of cracks
How is Subsidence Caused? (1 of 2)
There are core causes and triggers:
Causes:
 Soil shrinkage: Clay and silt
 Running water: can wash soil away.
 Man Made: Mining, in fill sites,
vibration (Fracking?)
Triggers:
 Trees and vegetation
 Leaking drains and water mains
 Man Made
How is Subsidence Caused? (2 of 2)
Soil Shrinkage is the predominant cause of subsidence in the UK >75%.
Soils are either cohesive or non-cohesive but both will contain water.
Cohesive (e.g. clay/silt)
 Volumetric change when wet or dry
 Clay is highly responsive to moisture
Non-Cohesive (e.g. sand & gravel)
 Running water washes fine particles away
PLUS:
 Decomposition – organic soils (Peat)
 Dissolve – chalk and limestone to create caves
that collapse and cause sinkholes.
Subsidence Triggers - 1of 3
Trees and Vegetation: 60% of all triggers
 Trees absorb water for photosynthesis Mature deciduous can remove >50,000L p.a.
 Dry periods – roots spread to search moisture
 Moisture removal can be up to 6m depth
 The desiccation zone (or zone of influence) is
the area from which a tree removes moisture
 The extent of the zone depends on tree type,
age and location of other trees
 Oak, Poplar and Willow regarded as worst
offenders
Subsidence Triggers – 2 of 3
Leaking Drains and Water Mains : 15-20% of triggers
 Water escaping softens the ground (or
washes away particles)
 Drains can be cracked & opened by
trees roots
 Drains are laid relatively low – trenches
filled with excavated materials. Drain
acts as sump and drawn in ground
water erodes trench = consolidation
and movement
Subsidence Triggers – 3 of 3
Man Made Triggers – 20-25% of triggers:
 Removal of support – excavations
around the foundations
(extensions/new drains/work on
adjacent land)
 Vibration can consolidate leading to
drop – usually caused by heavy and
constant traffic
 Changes in water table – often caused
by sinking of a new well
Issues Similar to Subsidence
Heave:
 Opposite of Subsidence – upward movement
of ground supporting building
 Only cohesive soils can heave
 Caused by removal of trees prior to
development
 Slow process – can take 30 years!
Landslip
 Movement of land mass down an incline or
slope to find a natural level
 Covered for inland only
 Caused by increase in natural water or leaking
drainage
Other Causes of Cracking
These are not usually covered within the insurance policy:
 Settlement
 Thermal Movement
 Lintel Failure – common when replacing
windows
 Chemical Attack
 Roof Spread (Tile replacement / solar panels)
 Cavity Wall Tie Failure
Subsidence in the UK
Last 10 years subsidence has cost economy >£3bn – costliest geohazard
1 in 5 properties is at risk of effects of shrink/swell
Annual incidents equal to flood
Subsidence through soil shrinkage represents the largest ground instability risk in the
UK
 The annual average insurer claims volume is 25,000 with costs of circa £250m – not
including hidden environmental impact. (Similar scale to fire claims)
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Swiss RE with Swiss Technology Institute predict up to 50% increase in subsidence across
Europe
Lender Approach
Lender approach is not as developed as that of insurer:
CML guidelines:
 Conveyancer must carry out searches appropriate to property (locality & features)
 Property must have insurance covering ‘subsidence, heave and landslip’
 May be a defect which is not covered by Valuation Report – recommended
borrower should instigate more detailed reports
Surveyor Valuation Report
 Report on visible damage or potential causes of damage – recommend further
investigations
 Asks customer to check on previous subsidence claims or known to neighbours
Where cracking, or previous subsidence the lender may:
 Withdraw offer
 Caveat offer subject to works completion
Insurer Approach – Policy Content
Policy Cover – Standard Wording
 ‘Subsidence or heave of the site upon which the buildings stand
or landslip’ Building is further defined
Subsidence on Site
 Policy wording: ‘The downward movement of the ground upon which the
building is founded for reason unconnected to the loading of the ground from the
building’.
 Oxford English : ‘the gradual caving in or sinking of an area of land’
 Confusion of settlement versus subsidence
 Case law – Barker vs. Lynch and NEM in 1990, the insurers sought to draw a
distinction between subsidence and settlement.
 Judge stated ‘subsidence is an ordinary English word, when in an insurance
policy will be read by ordinary people and it must therefore have an ordinary
meaning’.
 The judge decided that the damage described as settlement due to building
weight was subsidence within the meaning of the policy.
Insurer Approach – Policy Content
Exclusions
 Policy excess is usually £1000 of each and every incident of damage
(residential)
 Caused by compaction of in fill (settlement not subsidence)
 Occurring whilst the buildings are undergoing demolition, structural alteration or
structural repair.
 Caused by settlement, shrinkage or expansion. (Avoid claims early in a
building’s life due to bedding down in constructional faults).
 Caused by river or coastal erosion
 Arise from defective design, materials or faulty workmanship.
 Arising from movement of solid floors unless the foundations beneath the
exterior walls of the home are damaged by the same cause and at the same
time.
Insurer Approach – Claims Process
Overview
 40-60% of all claims are repudiated
 First phase = investigation, move to immediate repair
 Usually project managed through technically qualified
person (in house/outsource)
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Investigation
Soil types
Trees & Vegetation – arboriculturst
Drains test – CCTV
Monitoring cracks
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Repair
BRE guidelines for subsidence and type of repair
Usual repairs are straightforward standard structure
Sub Structure stabilisation – Underpinning or Micropiling
Certificate of Structural Adequacy
Insurer Approach – Liabilities
Liability under contract
 A surveyor undertaking a survey – contract has implied condition that conducted
as per professional standards.
 Failure (to detect the patent existence of subsidence damage) = breach of
contract.
Liability in tort of negligence
 Key factors: first a duty of care, second – breached, third – loss in consequence.
 Builder must build with reasonable skill and care, complying with standards of the
day
 Surveyor duty to borrower – reliance on report in proceeding with purchase
 Architect, surveyor, engineer design or supervising building works.
Liability in tort of nuisance
 Key factor – must be damage
 Common subsidence related is tree root trespass and damage.
Insurer Approach – Liabilities
Liability Under Statute
 Defective Premises Act 1972
 Duty of house builder to build dwellings properly
 Duty of care with respect to work done on premises
 Landlord duty of care to repair premises
 Construction and installation in dwellings
 Company/person providing instruction and all subcontractors
 Party Wall Act 1996
 Authorises work that would otherwise constitute trespass
 Work on existing wall, build new wall, excavate near neighbouring
building
 Costs
 Coal Mining Subsidence Act 1991
 Duty of British Coal Corporation to undertake/pay for remedial works
 Payment for depreciation in property value
Insurer Approach – Recoveries
Recovery
Examples
Vendor
Misrepresentation (Ridge vs Crawley), Defective Premises Act 1972
Surveyors, Architects and
Engineers
Pre-purchase surveys
Builder
Defective Premises Act 1972
Local Authorities
Building Regulations negligence, tree root trespass
Adjoining Property Owners
Failure to maintain, Third Party Wall Act, Tree nuisance, non natural user
Water Companies
Water Industry (Scheme for Adoption of Private Sewers) Regulation (2011):
 Water companies now ‘own’ sewers from property
 Leakage drains = 15% of subsidence issues
 Case for pursuit of damages against Water Companies – no precedent
yet.
Contribution Parties
ABI Domestic Subsidence Tree Root Claims
Agreement Third Party Liability (1997)
 Aim – to simplify claims from root trespass and
nuisance for private individuals
 When claim from neigthbour’s tree, building insurer
places tree owner on notice of the established
nuisance and request mitigation actions.
 Tree owner must contact their contents insurer
 Failure to mitigate, and further movement, =
recovery action against the adjoining occupier
 Note: Liability cover resides with the contents
insurer
Insurer Approach – Key Case Studies
Leading decisions on liability and causation:
 Patterson vs Humberside County Council (1995). Claimant must establish that
neighbouring trees were ‘effective and substantial’ cause. Susceptibility to subsidence is
immaterial.
Capacity to Sue
 Delaware Mansions Limited vs City of Westminster (2001).
 Prior to sale engineers stated structural damage by roots from local authority tree.
 Initial Court ruled Claimant could not sue for costs as damage was prior to freehold
 Court of Appeal overruled and upheld by House of Lords
 Nuisance existed prior was irrelevant & Defendant can give notice/reasonable opportunity to
abate before liability for expenditure can arise
Foreseeability of damage
 Russell vs London Borough of Barnet (1984) – local authority has knowledge of trees
 Greenwood vs Portwood (1984) – domestic owner no knowledge
• Butcher vs Perkins – domestic tree owner should know
• Court usually adopt Greenwood
Subsidence Risk Services
Current Situation:
 No objective method in place – yet largest geohazard in UK
 Current risk is based on geology only – broad soil type with shrink/swell capability
 What does that mean and what do I do?
Landmark, in association with Property Assure, introduces a new range of subsidence risk
assessment and risk management services.
• The first reports to use subsidence claims data and subsidence experts to determine
subsidence risk
• The reports don’t jack flag up issues; they provide guidance, risk management approaches
to reduce subsidence risk
• A full range of investigative services – no unanswered questions
• The reports provide an explanation of subsidence and its causes with a further wealth of
information available at a new dedicated website – www.subsidencesupport.co.uk
• Technical Helpline – Experts are a call away to help you with any aspect of subsidence
“Subsidence Risk Rating – Postcode”
The first objective evaluation tool to validate subsidence risk from
soil movement.
Its key features are:
 England and Wales only
 Provides risk at detailed postcode level (i.e. BN3 7BD)
 Core content – clay shrinkage and drainage related subsidence
 Risk is calculated from actual subsidence claims information
 4 levels of risk (variance to average) – Low, Medium, High and Very High
 Average is calculated as:
Total number of jobs / total number of residences in postcodes (containing at
least one property)
 Contains further information on subsidence, its causes, what to do to reduce
the risk and what further options are available.
Subsidence Risk Rating - Postcode
When to order?
 Subsidence Risk varies within Postcode areas, district, sector
 Risk Alert System will flag postcode districts where very high/high risk
postcodes sectors exist
Peterborough
District
Very High/High
Medium/Low
District
Very High/High
Medium/Low
PE1
PE1 4
PE1 1, PE1 2,
PE1 3, PE1 5
PE6
PE6 0, PE6 7, PE6 8
PE6 9
PE2
PE2 5, PE2 6, PE2
7, PE2 8, PE2 9
PE7
PE7 0, PE8 1, PE7 2
PE7 8
PE3
PE3 6, PE3 7, PE3
8, PE3 9
PE8
PE8 4, PE8 5, PE8 6
PE4
PE4 6
PE9
PE9 1, PE9 2, PE9 3,
PE9 4
PE5
PE5 7
PE10
PE10 0
PE4 5, PE4 7
PE10 9
Subsidence Risk Rating – Postcode
Interpreting Results
Suggested approach; however driven by the
customer’s attitude and requirements:
 Low/Medium – there may be a possible
subsidence issue however low need for
further investigation. Check trees
(extensive) – require consideration.
 High/Very high. Need to view the specific
property to understand the extent of
influencers. This may identify whether there
are trees and vegetation and information on
the property age and draining. It may be
worthwhile to consider further investigations.
Investigation Services
 Subsidence Risk Rating – Property
• Use when Very High/High
• Site visit collecting site specific information – soil, drainage, trees and location.
Surveyor review and opinion on key risks and effective mitigation requirements.
• Subsidence Risk Report – Specific Defect
• Use when cracking identified in property, signs of historic movement or previous
subsidence repairs
• Qualified Building Surveyor checks cracking or with previous subsidence checks the
Certificate of Structural Adequacy and the current state of the repairs.
• Subsidence Risk Report – Arboriculture
• Use when vegetation is identified as an issue
• Full site inspection of trees and shrubs against subsidence and duty of care with full
plan of works required.
• Subsidence Risk Report – Drainage
• Particularly relevant with glazed clayware drainage pipes
• Full drainage survey including CCTV and report of waste and storm pipes
How Do I Select What is Needed?
Subsidence Risk Rating – Postcode
undertaken
Result:
Result:
Low/Medium Risk
Consider checking trees and drains
Very High/High Risk
Any subsidence related
issues in Valuation
Survey
No
Signs of
Cracking/previous
Movement?
Yes
Numerous Trees
close to property?
Subsidence Risk Rating – Property to
provide property specific risk assessment
Subsidence Risk Report – Specific Defect
Yes
Subsidence Risk Report – Arboriculture
Yes
Salt glazed pipework
Or old property?
Subsidence Risk Report – Drainage
Subsidence Risk Mitigation
Trees and Vegetation
Tree management strategies are considered to mitigate any future risk:
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If trees too close and planted after the property was built, relocate.
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If trees too close, and planted before property built, manage by pollarding and crown
thinning. Do not remove without specialist advice – could cause heave.
Note restrictions:
• Cannot move or alter trees with Tree Preservation Order (TPO) or if in conservation
area. Must seek consent/advice from Local Authority.
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Trees that are not within the owner’s property boundaries.
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Mitigation in respect of local authority trees can be problematic. The Joint Mitigation
representatives to produce a guide and structure as to the process of tree migration
activities. JMP is available from London Tree Officers Association
(website: www.ltoa.org.uk)
Subsidence Risk Mitigation
Drainage
• General maintenance checks should be carried out.
• Checks should be made for blocked or leaking drains; dirt and leaves cleared
from gutters; and pipes checked to make sure there are no splits.
• It is particularly important to carry out these inspections on older properties
where the drains comprise of salt glazed clayware pipework. (Root ingress is
not uncommon leading to increased leakage)
• Minimum recommendation – manholes are lifted and inspected on an annual
basis.
• Any concerns of the drainage system integrity, a specialised CCTV survey can
be undertaken to assess its condition.
Subsidence Risk Services
Easy to use
Service
Subsidence Risk Rating Postcode
Price (Ex VAT)
Average Turnaround
£15
1 working day from receipt
Subsidence Risk Rating – Property
£265
10 working days
Subsidence Risk Report - Specific
Defect.
£375
10 working days
Subsidence Risk Report Arboriculture
£419
10 working days
Subsidence Risk Report Drainage
£318
10 working days
Summary
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Subsidence is equivalent to flooding in terms of number of incidents in annual average
and events. European forecast for subsidence increase.
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Subsidence through soil shrinkage is the largest cause of subsidence accounting for 75%
of incidents.
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There are a number of core causes of subsidence, many of which require a further,
known trigger.
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Lenders approach is not as developed as insurers – need to understand policy content
and definitions.
•
Subsidence, policy, definition and management approaches evolving. Codes of Practice
developed by ABI and other interested parties.
•
Legal precedence set for many aspects of subsidence – change in Sewer Ownership
2011 not precedent as yet.
•
Subsidence risk assessment developed from actual claims information and claims
management expertise
Some other reports available...
Webinar CPD Information & Disclaimer
CPD Ref: EGM/LING
This course is not intended to give legal advice and should
not be relied on. It is not to be regarded as a full statement
of law and practice in this area and specific advice should be
taken on matters of concern.
STL
www.stlgroup.co.uk
Tel: 0800 318611
or email: info@stlgroup.co.uk