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The Institution of Structural Engineers

AUGUST 2000

The Institution of Structural Engineers11 UPPER BELGRAVE STREET SW1X 8BH

Subsidenceof low-rise buildings

SECOND EDITION

A guide for professionalsand property owners


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Constitution of Task Group

2 IStructE Subsidence of low rise buildings 2nd edition

B P Clancy, JP, BSc(Eng), CEng, FIStructE, FICE, ACIArb, FASI, (UK Subsidence Group), Chairman (Consultant)F Allen*, CEng, MIStructE, (Cunningham UK Ltd.) (Loss Adjusters)Rev F J Atkins, CEng, MIStructE (National House-Building Council) (Building standards/Insurer)P G Biddle**, MA, DPhil, FArborA (Arboricultural Consultant)J Biller, CEng, MICE (Royal & Sun Alliance plc) (Insurers)D F Cutler**, BSc(Hons), DIC, PhD (Royal Botanic Gardens, Kew) (Botanist)

M Fisher, ARICS (Halifax plc) (Lenders)R B George, ACII, FCILA (McLarens Toplis) (Loss Adjusters)R A Jones, CEng, MIStructE, MIGasE, FBEng (London Borough of Southwark) (Local Authority Building Control)C Munnings***, ACII (AXA Insurance plc) (Insurers)J C W Patch, BSc (Roger Bullivant Ltd) (Contractors)J Pryke, MA(Cantab), CEng, FIStructE, FICE (Consultant/Contractor)C G Rae, FRICS (Abbey National plc) (Lenders)J C Smith, Cert Arb (RFS) (London Tree Officers Association) (Arboriculturists)J E A Tapsell, CEng, FIStructE, MICE (Tapsell, Wade & Partners Ltd.) (Consultants)W Thompson, IEng, AMIStructE (Van Elle Ltd.) (Contractors)D A Travis*, BEng(Hons), CEng, MIStructE (Cunningham UK Ltd.) (Loss Adjusters)

Secretary to the Task GroupB Chan, BSc(Hons), AMIMechE (Institution of Structural Engineers)D Wiltshire, CEng MIStructE (Former Secretary to the Task Group)

Corresponding memberJ Batten, ACII (Royal & Sun Alliance plc) (Insurers)N Spring-Benyon*, BSc(Hons) CEng MICE ACII (Ellis & Buckle) (Loss Adjusters)A Whitehead, Dip Arb (RFS) FArborA (A Whitehead) (Arboricultural Consultant)

*Cunningham UK Ltd. merged with Ellis & Buckle in November 1998.** representing the Arboricultural Association.*** representing the Association of British Insurers.

The following additional people served on the original Task Group that produced the first edition and whose efforts arereflected in the second edition:

M Abbott CEng MIStructE MIAS (Southwark District Surveyors)A Boobier BEng(Hons) CEng MICE FCILA (Robins South Ltd)

R A Bullivant BSc(Eng) CEng FIStructE FICE (Roger Bullivant Ltd)W Carson CEng MIStructE MIBC (Glasgow City Council)E S Coady FRICS (Abbey National plc)T Freeman MA CEng MICE (Geo-Serv Ltd)P D Johnson BSc(Eng) CEng MICE (Sun Alliance Insurance)Professor G S Littlejohn BSc(Hons) PhD FEng FIStructE FICE (University of Bradford)A K Moores CEng FIStructE ACIArb MWeldI (S B Tietz & Partners)D Spencer FRICS (Leeds Permanent Building Society)P Kitchen (Consumers Association)

Published by SETO, 11 Upper Belgrave Street, London SW1X 8BH

First edition published 1994

ISBN 1 874266 54 9

2000 The Institution of Structural Engineers

Produced by Andy Lorans/Choni Barrio for SETO

The Institution of Structural Engineers and the members who served on the Committee which producedthis report have endeavoured to ensure the accuracy of its contents. However, the guidance andrecommendations given in the report should always be reviewed by those using the report in the light of thefacts of their particular case and specialist advice obtained as necessary. No liability for negligence orotherwise in relation to this report and its contents is accepted by the Institution, the members of theCommittee, its servants or agents.

No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form orby any means without prior permission of the Institution of Structural Engineers, who may be contacted at11 Upper Belgrave Street, London SW1X 8BH.


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Contents

IStructE Subsidence of low rise buildings 2nd edition 3

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141.2 Historical perspective . . . . . . . . . . . . . . . . . . . . . . . . .14

1.2.1 Clarification of the problem . . . . . . . . . . . . . . . 14

1.2.2 Reaction to the problem. . . . . . . . . . . . . . . . . . . 14

1.3 The Institution initiative . . . . . . . . . . . . . . . . . . . . . . .15

1.3.1 Establishment of the Task Group in 1992 . . . . . 15

1.3.2 Consultation with other bodies . . . . . . . . . . . . . 15

1.3.3 Reforming the Task Group in 1998 . . . . . . . . . . 16

1.4 Customer care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

1.5 The Expert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

1.6 Codes of Practice, Standards & Regulations, etc. . . . .16

2 Explanation of terms . . . . . . . . . . . . . . . . . . . . . . . . . . .17

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

2.2 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

2.2.1 Technical terms . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2.2 Insurance terms . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2.3 The technical expert adviser (The Expert) . . . . 20

2.2.4 Glossary of qualifying bodies for Experts. . . . . 21

2.3 Mortgage procedure the relationship between

Lenders, Borrowers, Insurers and Valuers . . . . . . . . .21

2.3.1 The mortgage. . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3.2 The role of the valuer . . . . . . . . . . . . . . . . . . . . 21

2.3.3 Insurance arrangements . . . . . . . . . . . . . . . . . . 22

2.3.4 Standard house purchase reports . . . . . . . . . . . 22

2.4 Supplementary reports . . . . . . . . . . . . . . . . . . . . . . . . .23

3 Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

3.2 Customer care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

3.3 Property owner (The Insured) . . . . . . . . . . . . . . . . . . .26

3.4 Lender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

3.5 Insurer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

3.6 Local Authority/Utilities . . . . . . . . . . . . . . . . . . . . . . .27

3.7 Neighbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

3.8 Contractor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

4 Insurance matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .304.2 The insurance contract . . . . . . . . . . . . . . . . . . . . . . . .30

4.3 Subsidence damage cover . . . . . . . . . . . . . . . . . . . . . .30

4.3.1 Insurance cover and its continuity . . . . . . . . . . 30

4.3.2 Establishing a claim . . . . . . . . . . . . . . . . . . . . . 30

4.3.3 Timing of subsidence damage . . . . . . . . . . . . . . 30

4.3.4 Reopening claims. . . . . . . . . . . . . . . . . . . . . . . . 31

4.4 Policy conditions and exclusions . . . . . . . . . . . . . . . .31

4.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4.2 Prompt notification . . . . . . . . . . . . . . . . . . . . . . 31

4.4.3 Non-disclosure. . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4.4 Sum insured . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4.5 Under insurance . . . . . . . . . . . . . . . . . . . . . . . . 31

4.4.6 Maintenance and repair . . . . . . . . . . . . . . . . . . 32

4.4.7 Betterment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.4.8 Floor slabs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.5 Investigation of insurance claims . . . . . . . . . . . . . . . .32

4.6 Handling of subsidence, heave and landslip claims . .32

4.6.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.6.2 Simple stabilisation measures . . . . . . . . . . . . . . 32

4.6.3 Continuity of cover after remedial works . . . . . 32

5 The causes of damage to buildings . . . . . . . . . . . . . . . .35

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

5.2 Differential movement . . . . . . . . . . . . . . . . . . . . . . . .36

5.3 Cracking due to movement of foundations . . . . . . . . .36

5.4 Causes of foundation movements that may lead to

structural damage . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

5.4.1 Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.4.2 Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.4.3 Volumetric changes to soil . . . . . . . . . . . . . . . . 37

5.4.4 Instability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.4.5 Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.4.6 Mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

5.4.7 Frost heave . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.4.8 Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.4.9 Chemical attack. . . . . . . . . . . . . . . . . . . . . . . . . 42

5.5 Superstructure damage not due to subsidence . . . . . . .43

5.5.1 Thermal movement . . . . . . . . . . . . . . . . . . . . . . 43

5.5.2 Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.5.3 Moisture movements . . . . . . . . . . . . . . . . . . . . . 43

5.5.4 Roof spread . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.5.5 Timber rot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.5.6 Masonry and brickwork damage. . . . . . . . . . . . 43

5.5.7 Poor design, detailing and workmanship . . . . . 44

5.5.8 Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.5.9 Lack of maintenance . . . . . . . . . . . . . . . . . . . . . 44

5.5.10 Movement due to changes in load patterns . . . 44

5.5.11 Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.5.12 Calcium silicate bricks . . . . . . . . . . . . . . . . . . 44

5.5.13 Bookend effect/thermal expansion. . . . . . . . . . 45

5.5.14 Direct root action . . . . . . . . . . . . . . . . . . . . . . 45

5.5.15 Mundic concrete . . . . . . . . . . . . . . . . . . . . . . . 46

5.5.16 Damage caused by subsidence of an

adjoining building . . . . . . . . . . . . . . . . . . . . . . 46

6 Initial appraisal of the property . . . . . . . . . . . . . . . . . .496.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

6.2 Objectives of the initial appraisal . . . . . . . . . . . . . . . .50

6.3 Suitable professional experts for the initial

appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

6.4 Damage threshold and the significance of

cracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

6.5 Procedure for the initial appraisal . . . . . . . . . . . . . . . .53

6.5.1 Basic factors . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

6.5.2 The age of the property and any alterations . . . 54

6.5.3 The type of movement and pattern of

any cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6.5.4 Proximity of property to trees and large

woody shrubs. . . . . . . . . . . . . . . . . . . . . . . . . . . 55

6.5.5 Proximity of the property to sloping ground . . . 55

6.5.6 The likelihood of leaking drains . . . . . . . . . . . . 56


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6.5.7 Likelihood of the property being on

subsidence-sensitive soils . . . . . . . . . . . . . . . . . 56

6.6 Identification of subsidence crack patterns . . . . . . . . .57

6.6.1 Identification of cracks related to various

types of buildings. . . . . . . . . . . . . . . . . . . . . . . . 57

6.6.2 Characteristics of subsidence cracks . . . . . . . . 58

6.6.3 Decorations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.7 Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

7 Further investigations . . . . . . . . . . . . . . . . . . . . . . . . . .637.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

7.2 Scope of further investigations . . . . . . . . . . . . . . . . . .64

7.3 Assessment of which parts of the foundation or

superstructure are stable . . . . . . . . . . . . . . . . . . . . . . .64

7.3.1 Full crack record. . . . . . . . . . . . . . . . . . . . . . . . 64

7.3.2 Distortion survey . . . . . . . . . . . . . . . . . . . . . . . . 64

7.3.3 Crack monitoring. . . . . . . . . . . . . . . . . . . . . . . . 64

7.3.4 Level monitoring . . . . . . . . . . . . . . . . . . . . . . . . 67

7.4 Soil investigation procedure . . . . . . . . . . . . . . . . . . . .68

7.4.1 Trial pits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

7.4.2 Boring and hand augering. . . . . . . . . . . . . . . . . 68

7.4.3 Probing penetration testing . . . . . . . . . . . . . . 69

7.4.4 Soil examination . . . . . . . . . . . . . . . . . . . . . . . . 707.4.5 Soil tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

7.4.6 Assessment of desiccation from soil tests . . . . . 70

7.4.7 Assessment of shrinkability . . . . . . . . . . . . . . . . 71

7.4.8 Calculation of heave/shrinkage potential . . . . . 71

7.4.9 Assessment of permeability and rate of

moisture recovery . . . . . . . . . . . . . . . . . . . . . . . 71

7.4.10 Identification of root samples . . . . . . . . . . . . . 71

7.5 Predisposing factors, and diagnosis of

their involvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

7.5.1 Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

7.5.2 Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

7.5.3 Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727.5.4 Traffic, or potential causes of vibration . . . . . . 72

7.5.5 Other building operations . . . . . . . . . . . . . . . . . 72

7.5.6 Changing environmental factors. . . . . . . . . . . . 72

7.6 Final report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

8 Trees and tree management . . . . . . . . . . . . . . . . . . . . . .758.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

8.1.1 Nature of damage . . . . . . . . . . . . . . . . . . . . . . . 76

8.1.2 The tree: crown-root balance . . . . . . . . . . . . . . 76

8.1.3 Water use and pruning . . . . . . . . . . . . . . . . . . . 76

8.2 Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

8.2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

8.2.2 Interpretation of root spread data. . . . . . . . . . . 778.2.3 Roots and drains . . . . . . . . . . . . . . . . . . . . . . . . 78

8.3 Remedial work on trees . . . . . . . . . . . . . . . . . . . . . . . .78

8.4 Root barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

8.5 Monitoring after remedial action to trees . . . . . . . . . .82

8.6 Tree management for prevention of subsidence . . . . .82

9 Subterranean, substructure and superstructurerepairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

9.1.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

9.1.2 Options for remedial works . . . . . . . . . . . . . . . . 86

9.1.3 Expectations of remedial works. . . . . . . . . . . . . 86

9.2 Ground stabilisation . . . . . . . . . . . . . . . . . . . . . . . . . .869.2.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

9.2.2 Repair of drains and leaking water mains . . . . 86

9.2.3 Control of ground moisture content . . . . . . . . . 87

9.2.4 Soil moisture management . . . . . . . . . . . . . . . . 87

9.3 Main topics of remedial works to foundations . . . . . .87

9.3.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

9.3.2 Traditional mass concrete underpinning. . . . . . 88

9.3.3 Beam and pier . . . . . . . . . . . . . . . . . . . . . . . . . . 88

9.3.4 Mini-pile systems. . . . . . . . . . . . . . . . . . . . . . . . 89

9.3.5 Jacking building back into previous position . . 94

9.3.6 Post tensioned and reinforced collar beams . . . 94

9.4 Guidance notes for engineers, contractors and

others responsible for remedial and underpinningworks contracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

9.4.1 Traditional mass concrete underpinning. . . . . . 96

9.4.2 Beam and pier underpinning. . . . . . . . . . . . . . . 98

9.4.3 Piles with beams or rafts . . . . . . . . . . . . . . . . . . 98

9.4.4 Jacked piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

9.4.5 Contractor proposals, workmanship and

quality control on site. . . . . . . . . . . . . . . . . . . 100

9.5 Partial underpinning . . . . . . . . . . . . . . . . . . . . . . . . .101

9.6 Repairs to superstructure . . . . . . . . . . . . . . . . . . . . . .101

9.6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

9.6.2 Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

9.6.3 Repair of plasterwork to walls, ceilings, etc. . 1029.6.4 Doors/window realignment . . . . . . . . . . . . . . . 103

9.6.5 Cosmetic repairs . . . . . . . . . . . . . . . . . . . . . . . 103

10 Remedial works to properties damaged bysubsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

10.2 The role of the Expert in remedial works . . . . . . . .106

10.3 Contract administration and procedures for major

remedial works . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

10.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

10.3.2 Pre-contract stage . . . . . . . . . . . . . . . . . . . . . 106

10.3.3 Design administration stage . . . . . . . . . . . . . 107

10.3.4 Contract and other insurance . . . . . . . . . . . . 10710.3.5 The pre-contract meeting . . . . . . . . . . . . . . . 107

10.3.6 Contract stage . . . . . . . . . . . . . . . . . . . . . . . . 108

10.3.7 Project management of the contract on site . 109

10.3.8 Work in the ground . . . . . . . . . . . . . . . . . . . . 109

10.3.9 Work above the ground . . . . . . . . . . . . . . . . . 109

10.3.10 Decoration. . . . . . . . . . . . . . . . . . . . . . . . . . 109

10.3.11 Final completion . . . . . . . . . . . . . . . . . . . . . 110

10.4 Health and safety matters relating to remedial

works contracts . . . . . . . . . . . . . . . . . . . . . . . . . . . .110

10.5 The Housing Grants Construction and

Regeneration Act . . . . . . . . . . . . . . . . . . . . . . . . . . .111

10.6 Building regulation matters . . . . . . . . . . . . . . . . . . .111

10.6.1 Scope of the regulations . . . . . . . . . . . . . . . . 111

10.6.2 How to ensure compliance with

the regulations. . . . . . . . . . . . . . . . . . . . . . . . 111

10.6.3 Building regulations as they apply to

foundations and underpinning. . . . . . . . . . . . 111

10.6.4 Scottish regulations . . . . . . . . . . . . . . . . . . . . 111

10.6.5 The scope of the regulations (Northern

Ireland) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

10.7 Guarantees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112

10.8 Certificate of structural adequacy . . . . . . . . . . . . . .112

11 Research & future activities . . . . . . . . . . . . . . . . . . .115

11.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11611.1.1 Activities identified in 1994 as requiring

attention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

11.1.2 Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116


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11.2 Particular research topics . . . . . . . . . . . . . . . . . . . .116

11.2.1 Root barriers . . . . . . . . . . . . . . . . . . . . . . . . . 116

11.2.2 BRE research into desiccation of

clay soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

11.2.3 HORTlink project Controlling water use

of trees to alleviate subsidence risk . . . . . . 116

11.2.4 Soil rehydration. . . . . . . . . . . . . . . . . . . . . . . 117

11.2.5 Mining subsidence. . . . . . . . . . . . . . . . . . . . . 117

11.2.6 Tolerance of structural movement. . . . . . . . . 117

Appendix A Mining subsidence . . . . . . . . . . . . . . . . . . .119

A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120

A.2 Coal mining subsidence . . . . . . . . . . . . . . . . . . . . . .120

A.2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . 120

A.2.2 Factors affecting mining subsidence. . . . . . . . 121

A.2.3 Estimation of subsidence. . . . . . . . . . . . . . . . . 122

A.2.4 Surface damage. . . . . . . . . . . . . . . . . . . . . . . . 124

A.2.5 Ground movement due to old coal workings . 125

A.2.6 Geometry of mine shafts . . . . . . . . . . . . . . . . . 126

A.3 Metalliferous mining subsidence . . . . . . . . . . . . . . .126

A.3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

A.3.2 Typical surface mining related features . . . . . 126

A.3.3 Investigation of metalliferous mining

subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

Appendix B Measures to minimise the effects of

foundation movement . . . . . . . . . . . . . . . . . . . . . . . . .131

B.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132

B.2 New build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132

B.2.1 Detailed site investigation. . . . . . . . . . . . . . . . 132

B.2.2 Desk study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

B.2.3 Walkover survey . . . . . . . . . . . . . . . . . . . . . . . 132

B.2.4 Physical investigation . . . . . . . . . . . . . . . . . . . 133

B.2.5 Identification of sites where special

precautions are required . . . . . . . . . . . . . . . . 133B.2.6 Factors relevant to selection of appropriate

ground improvement and foundation types . . . 134

B.2.7 Ground improvement methods . . . . . . . . . . . . 134

B.2.8 Selection of foundation type . . . . . . . . . . . . . . 135

B.3 Existing structures . . . . . . . . . . . . . . . . . . . . . . . . . .138

B.3.1 Factors within the property owners control . 138

B.3.2 Possible effects of excavation for adjacent

construction activity on existing buildings . . . 140

B.4 Mining subsidence precautions . . . . . . . . . . . . . . . .140

B.4.1 Precautions taken during mining . . . . . . . . . . 141

B.4.2 Structural considerations to minimise the effects

of mining subsidence . . . . . . . . . . . . . . . . . . . . 141

B.4.3 Consolidation of mine workings . . . . . . . . . . . 142

B.4.4 Shafts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

B.5 Treatment of site with natural cavities . . . . . . . . . . .144

Appendix C Sample certificate of structural

adequacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145

Appendix D Specimen underpinning guarantee . . . . . .149

Appendix E ABI Domestic Subsidence Agreement &

Tree Root Claims Agreement . . . . . . . . . . . . . . . . . . .153E.1 ABI Domestic Subsidence Agreement . . . . . . . . . . .154

E.1.1 The Agreement . . . . . . . . . . . . . . . . . . . . . . . . 154E.1.2 Guidance on the Agreement . . . . . . . . . . . . . . 155

E.2 ABI Domestic Subsidence Tree Root

Claims Agreement . . . . . . . . . . . . . . . . . . . . . . . . . .157

E.2.1 The Agreement . . . . . . . . . . . . . . . . . . . . . . . . 157

E.2.2 Guidance on the Agreement . . . . . . . . . . . . . . 158

Appendix F Building Regulations . . . . . . . . . . . . . . . . .159

F.1 Building Regulations (England & Wales) . . . . . . . .160

F.1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . 160

F.1.2 Requirements of the regulations . . . . . . . . . . . 160

F.1.2.1 Part A: Structure . . . . . . . . . . . . . . . . .160

F.1.2.2 Other requirements . . . . . . . . . . . . . . .161

F.1.3 Scope of the regulations . . . . . . . . . . . . . . . . . 162F.1.3.1 Exemption by Schedule 2 . . . . . . . . . . .162

F.1.3.2 Exemption by prescription . . . . . . . . . .162

F.1.3.3 Crown property . . . . . . . . . . . . . . . . . .162

F.1.4 Application of the regulations. . . . . . . . . . . . . 162

F.1.4.1 Full plan route . . . . . . . . . . . . . . . . . . .163

F.1.4.2 Building notice route . . . . . . . . . . . . . .163

F.1.5 Building regulations as they apply to

underpinning . . . . . . . . . . . . . . . . . . . . . . . . . 163

F.1.6 Building control reverting to a local

authority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

F.1.7 Regularisation. . . . . . . . . . . . . . . . . . . . . . . . . 163

F.1.8 Building regulation charges . . . . . . . . . . . . . . 163

F.1.9 Building over a sewer . . . . . . . . . . . . . . . . . . . 163

F.1.10 Determinations . . . . . . . . . . . . . . . . . . . . . . . 163

F.1.11 Relaxations or dispensations . . . . . . . . . . . . 163

F.1.12 Requirements of other related legislation. . . 164

F.1.12.1 Inner London . . . . . . . . . . . . . . . . . . .164

F.1.12.2 Other local Acts . . . . . . . . . . . . . . . . .164

F.1.12.3 Other relevant legislation . . . . . . . . .164

F.2 Scottish regulations . . . . . . . . . . . . . . . . . . . . . . . . . .164

F.2.1 Introduction Building standards (Scotland)

Regulations 1990. . . . . . . . . . . . . . . . . . . . . . . 164

F.2.2 Part A: Structure. . . . . . . . . . . . . . . . . . . . . . . 164

F.2.3 Part C: Structure. . . . . . . . . . . . . . . . . . . . . . . 164

F.2.4 Further requirements . . . . . . . . . . . . . . . . . . . 164F.3 Northern Ireland regulations . . . . . . . . . . . . . . . . . . .165

F.3.1 Building regulations order . . . . . . . . . . . . . . . 165

F.3.2 Scope of the regulations . . . . . . . . . . . . . . . . . 165

F.3.3 How to ensure compliance with the

regulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

F.3.4 Regulations as they apply to foundations . . . 166

Appendix GParty Wall, etc. Act 1996 . . . . . . . . . . . . . .169

G.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

G.2 Scope of the Act . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

G.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

G.4 Notices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

G.4.1 Work to an existing party wall . . . . . . . . . . . . 170

G.4.2 New wall astride a boundary line. . . . . . . . . . 170

G.4.3 New wall against the boundary line . . . . . . . . 170

G.4.4 Excavation near neighbouring buildings . . . . 170

G 5 Dispute procedure . . . . . . . . . . . . . . . . . . . . . . . . . . .171

G.6 Award . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

G.7 Costs of work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

Appendix H Acknowledgements . . . . . . . . . . . . . . . . . .173


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8/177


Foreword

The original Guide was published in March 1994 and has since then been the authoritative

reference on the subject of subsidence of low-rise buildings. Following recommendations inthat edition the subject has moved forward, particularly in the case of claims for subsidencedamage to domestic property where Insurers are involved. This has been accompanied bythe widespread adoption of our recommendation that matters can be more quickly resolvedto the satisfaction of both Insurers and the Insured (the householder) if procedures are basedon co-operation rather than confrontation.

One of the most important points for Insurers and Lenders to appreciate is that proceduresdeveloped over the last 10 years now deal with the problem of subsidence well. Therefore torefuse to lend on, or to insure, a property that has suffered subsidence in the past, which hasbeen properly appraised and dealt with, is not reasonable. It will exclude an ever-increasingproportion of the housing stock. Subsidence claims now average about 40,000 cases eachyear and there is no reason to suspect that this rate will reduce in the foreseeable future.

There has been a substantial reduction in the use of disruptive and costly underpinning tosolve subsidence problems over the last 5 years. The emphasis has changed to consideringalternative less disruptive means of stabilising affected properties.

In recent years it has been statistically shown that trees and other large vegetation on claysubsoil are responsible for over 65% of all instances of subsidence damage to domesticproperty that percentage is even higher during drought years. The presence of trees clearlyadd value to an area and its property. This edition of the Guide advocates and advises ontree management and recommends felling of trees only in exceptional circumstances.

The Guide continues to recommend that, like any other form of property maintenance,householders should regularly address tree management. Tree owners have a responsibilityto all adjacent properties, whether they own them or not, so good relations are importantbetween property owners and the tree owners. This time the Task Group had threeArboriculturists/Botanists among its members Giles Biddle, David Cutler and Jim Smith.

David and Giles were nominated to our group by the Arboricultural Association; Jim wasnominated by the London Tree Officers Association. I am especially grateful to them fortheir help on this difficult topic.

Previously Insurers expected the Insured to have proved their subsidence claim beforethey were prepared to accept it. Most claims are now handled by Insurers who themselvesdirectly appoint Experts to investigate notified claims. This is a much more efficient proce-dure, which also minimises the likelihood of disputes between householders and Insurers.

Again the Task Group has consulted widely in order that the Guide will be as relevant andcomprehensive as possible. The Association of British Insurers, the Royal Institution ofChartered Surveyors, the Arboricultural Association and Association of Building Engineershave all been most helpful with comments. As Chairman of the Task Group, I must say thatI am also very appreciative of all those other individuals and organisations that wrote in to

give their views; all were carefully considered and many incorporated in this new edition.Names of those who offered comments are recorded in Appendix H.As with the first edition, I would again like to thank all those who served on the Task

Group for the immense contribution which they have made to the drafting of this secondedition. They brought an equal degree of professionalism and dedication, as did those mem-bers who served on the first Task Group. Some are common to both and a number of theoriginal team have also commented most helpfully on this edition. To all of them, and to thefirms and organisations which they represent, I give my thanks and appreciation.

I am conscious that the Institution has many technical and professional matters in train forpublication and I wish to thank the Engineering Committee and the Council for allowing meto persuade them that this second edition was required so soon after the first.

Finally but by no means least I wish to thank the Institution staff involved in the prepara-tion of this new edition and particularly Berenice Chan, our Task Group Secretary. Theremarkably short pre-publication period achieved is substantially due to her efforts.

In my view it has been an excellent team effort. I am sure that this new edition will be assuccessful as its predecessor and that it will build on the considerable progress which that


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original edition brought to a subject which was, at the time in 1994, in something of a stateof chaos. Yet it is a subject which intimately affects the lives of hundreds of thousands ofordinary people.

All members of the Task Group hope that this second edition of the Guide will be of ben-efit to all whose property is experiencing subsidence as well as those called upon to adviseand deal with subsidence problems.

Brian ClancyTask Group Chairman

August 2000

1. This Guide has been drafted to meet the needs of a wide readership includingMortgage Lenders, Consulting Engineers, Property Valuers, Insurers, Builders,Solicitors, Surveyors, Loss Adjusters, Local Authorities and property owners.

2. Technical formulae and specialist jargon have been kept to a minimum, to enable theordinary householder and other non-specialist to gain a comprehensive understandingof subsidence from this Guide.

3. Although the Guide focuses on domestic property, it is readily applicable to all low-rise buildings irrespective of use.

4. The technical issues in the Guide are common to low-rise buildings throughout theUK. The insurance procedures outlined in the Guide reflect the current situation inEngland. However, whilst procedures vary from one region to another, the principleson which they are founded hold true across the UK.

5. Definitions of technical, insurance and other terms given in the Guide are those used inthe first edition; they are consensus definitions based on present day common usageand understanding. But it is acknowledged that some variance of terminology exists in

specialist fields.6. Some repetition of material occurs in the Guide for the convenience of those wishingto dip into the Guide for specific information. This repetition avoids the irritation ofexcessive cross-referencing.

7. The whole process of handling a potential subsidence case from its identificationthrough to its solution, is outlined in the flowchart beginning on the opposite page.

8. Each chapter is prefaced by a detailed contents list to guide the reader through the text.9. Names in brackets in illustration captions acknowledge their source.

Notes for readers of the 2nd edition


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Insurer

Building insurance policy

Direct from Insurer

Purchase of insurance policy

Through broker

Insureds Expertif appointed

Through lender

Damage to policyholders

propertySubmit claim form

Specialistconsultant

Position monitoringstuds

Drainagecontractors Arboric

Soil sampleand testing

Tree rootidentification

Specialist siteinvestigation

Appoint specialistconsultants/contractors/

laboratories as appropriate

Report to insured andinsurer with advice on

further action/investigation

Advise Insured ofreasons for not

accepting claim butalso action required

on property, e.g.repair of defects

Report to Insuredand Insurer

Claim declined byInsurer

Expert on approved list main alternatives:

Insured

Insurer

Inspection andinitial appraisal of

property

Furtherinvestigations

Specialistconsultant

Loss adjusterusing in-housetechnical expert

advisers

Loss adjusterusing specialist

consultant

A

Possiblesubsidence

damage

Damagecaused by

other insuredperil?

ContinuetoadviseInsured

Initialinsuranceclaiml

iaisonstage

Chapters5-6(possibl

eChapter8)

Initialclaiminvestigationapprovalstage

Liaise

Appoint & liaise

No

Yes

Yes

No

Chapters2-4

Flowchart

for the handling

of a potential

subsidence claim

GO TO TOP OF PAGE 10


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A

B

Furtherinvestigations

Monitor to identifypattern of movementand probable cause

Persistant moisturedeficiency implications

Type, depth offoundation and nature

of ground beneath

Trial holes

Drains testExpose drain

junctions

Tree root identificationif required Soil analysis

Causeother

Put adjoiningowner on

notice

Possible causetrees see 7.5.1.

Obtain arb.report with

recommendation

Consult LAon TPOs

Remove/prunetrees

Continuemonitoring

Trial hole data

Siteinvestigation

report

Contractorsdesign

Partial or completeunderpinnning

scheme

Design underpinningscheme and

superstructure scheme

Obtain tenders

Appoint Contractor(s)

Pre-contract meeting

Review position onContractorsguarantees

Detailedspecification

Buildingregs

CDMRegs

Partywall act

Apply as

appropriate

Completion of agreedmonitoring period

Preparesuperstructure repair

specification

Invitecontractorsto tender

Appointsuperstructure

repair contractor

Insurersapproval

Insuredsapproval

Cause defectivedrains

Repair drains

Suspect leakingdrains possible

trial holes

Onpolicyholders

land

Is anarb. reportnecessary

Isproperty

likely to remainstable infuture?

Insurers

(Expert)design

Insurers(Expert)check

Isfurther

site investigationrequired

Hasproperty

stabilised?

Furtherinvestigationstage

Chapters7-8

Other cause?

Minor

Major

No

No

Yes

Yes

Yes

Yes

Yes

Yes

No

No No

No

No

Drains?

CONTINUED FROM PAGE 9

CONTINUED OPPOSITE ON PAGE 11

Site investigation toenable underpinnning

design


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B

Pre-contractmeeting

Take possessionof site

Superstructure works

Redecoration asagreed with claimant

Final completion

Defects liability period

Payment of Expert

Certificate of structuraladequacy

Result of process

Property saleable and insurance

capable of being continued toexisting or new owner

Improved customerservice quality

Inspection of works

Contractinstructions

Final paymentcertificate

Final payment

Contractorsguarantee

Interim paymentcertificates

Interim payments

Building control

Site inspections Underpinning works

Contractor

Expert

Contractor

Programme of works

LA planningmatters/building regs

Minutes distributedby Expert

Photographic record

Inspect adjoiningproperties

Discuss bettermentitems

Discuss Insuredsinterests

Payments to contractor

Protection of works& adjacent areas

Need for progress/sitemeetings

Expert/inspectionof works

Insured

Items to consider, e.g.

Precontract

Contractadministration

Chapters9/10

Handover

Notify

To Insured &lender

To Insured &lender

CONTINUED FROM PAGE 10


13/177



14/177


Chapter 1

Background

1.1 Introduction 14

1.2 Historical perspective 14

1.2.1 Clarification of the problem 14

1.2.2 Reaction to the problem 15

1.3 The Institution initiative 15

1.3.1 Establishment of the Task Group in 1992 15

1.3.2 Consultation with other bodies 16

1.3.3 Reforming the Task Group in 1998 16

1.4 Customer care 16

1.5 The Expert 16

1.6 Codes of Practice, Standards & Regulations, etc. 16


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1.1 Introduction

The intention of this publication is to provide as much up todate information as possible to encourage a more rationalapproach to damage and loss caused by subsidence, heaveand landslip, and repair of affected buildings. Although this

Guide confines itself to dealing with low rise, conventionallyconstructed buildings, i.e. those up to four storeys in height,the principles discussed can also be applied, where appropri-ate, to much larger buildings. The guidance given can there-fore be applicable to virtually all domestic properties, excepthigh-rise flats. The technical principles which are addressedcan also be applied to low-rise buildings used for commercialpurposes. The insurance information given in the Guide isapplicable only to domestic properties. It is however recog-nised that not all buildings are insured.

The general public are to be excused for believing that sub-sidence and heave of buildings are relatively recent problems.This is because they were only generally included as insuredrisks in household policies after 1971. It is, therefore, onlysince then that the public have been particularly aware of

them.Subsidence and heave have in fact always affected build-

ings under certain ground conditions, but in the past, cracksand other damage resulting from them were normally attend-ed to by building owners as part of routine maintenance. Veryfew buildings required major remedial works, although onlybuildings constructed on very stable hard material, such asrock, are likely to avoid this type of damage completely.

Prior to the 1970s subsidence, heave, settlement, con-solidation, compaction and similar terms were used some-what interchangeably by both specialists and lay persons tomean more or less the same thing as regards ground move-ment. Since then, the lack of specific definitions for groundmovements generally within insurance policies can lead tofrequent misunderstandings.

1.2 Historical perspective

1.2.1 Clarification of the problemInitially, in the early 1970s there were very few subsidenceclaims and Insurers tended to meet them in full with littleregard for the extent to which the repairs might be justifiedfrom a technical point of view. In the twenty years or sobefore this Guide was first written, various parties hadattempted to define subsidence, but such definitions had notreceived universal acceptance because it was thought thatthey could possibly have been produced by sectional interests

for their own benefit.Insurance cover against subsidence, heave or landslip dam-

age was introduced in 1971 to accommodate Lenders in pro-tecting both their loan security and their customers againstmajor catastrophe (see Fig. 1.1). This cover has increasinglycaused difficulties over the last 25 or more years, particularly inhow subsidence, heave and landslip damage was to be appraisedand dealt with. These difficulties were never anticipated.

Insurance cover against subsidence, heave and landslipdamage has unintentionally developed to become a form ofgeneral building maintenance paid for by Insurers at enor-mous cost and used for the repair of thousands of propertiesshowing only the slightest signs of subsidence damage. Thiscost must eventually be reflected in higher premiums for all.The main problem has been the failure of all involved to

anticipate and answer the following questions:

What is subsidence, is it different from settlement, andwhat is heave?

In what circumstances is it reasonable to conclude that aproperty requires remedial work to overcome the resultsof subsidence or heave?

What form should that remedial work take? Is it reasonable for an Insured to expect an Insurer to pay

for the repair of structurally trivial damage, even if it is

technically the result of subsidence, when there is a pos-sibility of the same sort of damage occurring again in thefuture because of continued slight movement in the prop-erty?

Is it reasonable to expect Insurers to pay for preventativeremedial work to a building or part of a building whichmay not have been actually damaged by subsidence,heave and landslip, but which might possibly be dam-aged in the future?

These and many more such relevant questions have onlycome to the fore since subsidence and heave cover has widelybecome available.

During the past 25 or more years since the introduction ofsubsidence insurance cover, there have been a number of

exceptionally dry periods such as 1975/76, 1984, 1989, 1990,1991, and 1995. During these years, subsidence claimsreached peaks which were completely unforeseen not only byInsurers but also by Experts (see Fig. 1.2). Thousands ofproperties throughout the country suffered structural move-ment, cracks appeared in walls and ceilings, and home-own-ers were obviously extremely worried for two reasons:

Were their homes becoming structurally unsound andtherefore dangerous?

Were their homes being affected so severely that theirvalue would decrease appreciably?

The first question was relatively easy to answer by obtainingtechnical advice from a Chartered Structural or CivilEngineer or Chartered Building Surveyor. The second ques-tion was more difficult. The value of anything is only whatothers will pay for it. Buyers will only pay the true value ifthose advising them on the value confirm that it is unaffectedto a significant degree by any defects.

There was no doubt that in the dry periods mentioned, anumber of properties suffered quite severe structural move-ment to the extent that even engineers had concerns abouttheir structural stability. However, thousands, almost certainlythe vast majority, suffered only minor damage.

Once it was realised by home owners that most properties

1 Background

Fig. 1.1 Example of major subsidence damage resulting fromcollapse of an underground canal


16/177


had insurance cover for subsidence damage, it was hardly sur-prising that claims were made by the owners against theirInsurers even for trivial damage. Unfortunately the extent towhich a property must be damaged before it technically justi-fied remedial works had never been defined by Insurers, sothe obvious course of action for the owner was simply tomake a claim and have the work attended to at the Insurersexpense. This has since given rise to problems and misunder-standings as Insurers sought to limit their losses in variousways, when they realised that they were effectively providinga maintenance service.

1.2.2 Reaction to the problemUnfortunately, the problem was not examined from first prin-ciples.

Typically, it was not recognised that building constructionover the preceding two or three decades had used less flexiblematerials. For example, hard cement mortar was introduced inplace of the traditional lime mortar for brickwork makingbuildings more brittle. As a result, modern buildings tend toshow signs of structural movement more dramatically thanolder, more flexible buildings, and even minor movementmay be sufficient to cause some visible damage.

Consequently, because individual Insurers were having to

meet many thousands of subsidence damage claims, theybecame much more reluctant to provide cover for any proper-ty with signs of subsidence damage or structural movement.

In addition, since the early 1970s, there has been a tenden-cy for an increasing public expectation of the structural per-formance, e.g. tolerance to minor cracking of buildings, andalso for a much higher quality service from their professionaladvisers. As a consequence, a number of court cases broughtagainst professional advisers proved successful with theinevitable result that these advisers became more conservativein the advice which they gave. Surveyors and Engineers,when asked to value or assess properties suffering from sus-pected subsidence damage or structural movement, found iteasier to recommend remedial works rather than appraise theproperties more objectively, even when the damage was rela-tively trivial. By adopting this approach, they reduced the riskof legal actions against them for negligence.

Finally and inevitably, many structural damage problemsare identified when properties are put up for sale. The small

amount of time available during this process to assess prob-lems of this sort places considerable pressure on all parties todeal with any problem promptly and to a standard which leftno doubt as to the future stability of the property. Indeed, themajor drought of 1975/76 caused such widespread damagethat for many years after it, Lenders were cautious about lend-ing on subsidence- and heave-damaged properties even afterthey had been repaired.

Originally, Insurers and their Experts adopted an over cau-tious approach which meant that thousands of properties suf-fering from relatively minor damage, caused by subsidence orheave, were underpinned. In the vast majority of cases thishas proved to be technically unnecessary. The problem couldhave been dealt with much more economically and objective-ly by taking the time needed to identify and deal with theactual cause of damage. However, the demand to get proper-ties repaired promptly generally meant that this option wasnot pursued.

Further dry summers have exacerbated an already unsatis-factory state of affairs to such an extent that there now existsa large industry geared solely to the underpinning of domesticproperties suffering from ground movement.

Statistics show that an extraordinary amount of money,running into hundreds of millions of pounds, has been spent

on largely unnecessary underpinning works and general main-tenance repairs. Most Civil and Structural Engineers wouldconsider such sums to be substantially unjustified in the con-text of technically appropriate repairs.

1.3 The Institution initiative

1.3.1 Establishment of the Task Group in 1992Initially discussions between a small number of StructuralEngineers established that any repairs to properties damagedby subsidence or heave should be dealt with by the applica-tion of basic technical principles. However because the wholeprocess was dictated by the expectations and demands ofhomeowners, Lenders and Insurers, it was clearly impractica-ble to deal with the problem solely in this way.

There is no doubt that ground movement-related damage tobuildings is basically an engineering problem but it is much

Fig. 1.2 Cost and number of claims 1975-99 (data from ABI)

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

No.

Claims(

000)

Cost(m)


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influenced by the wish among owners and mortgage Lendersto ensure that the value of a building should not be signifi-cantly affected by damage which that building might suffer,from whatever cause.

While the initiative for a Task Group was promoted by theInstitution of Structural Engineers, it was decided to extendits membership to include other interested parties outside theInstitutions membership so that the subject could be lookedat on as broad a basis as possible. Accordingly representativesfrom these groups who were technically and professionallyqualified and in particular familiar with subsidence or adirectly related subject, were invited to participate.

1.3.2 Consultation with other bodiesAlthough the original Task Group had the benefit of two veryexperienced underpinning contractors among its number, itwas decided that a full-day seminar would be held at theInstitution of Structural Engineers with attendance restrictedto delegates from contracting firms who were known to spe-cialise in remedial and repair work to buildings, particularlythose damaged by ground movement. This was held inNovember 1992 and over 80 delegates attended with repre-sentation from 23 different companies. Comments from thisseminar were taken on board and incorporated into the Guide.

Through the Council of Mortgage Lenders and the

Association of British Insurers, the original Task Group con-sulted as widely as possible to ensure that all interested par-ties could comment, if they wished, as the framework of theGuide developed. In addition, the existence of the Task Groupwas advertised in the technical and national press and as aresult many individuals and organisations made representa-tions to the Task Group and, again these were all taken intoconsideration during the preparation of the Guide. A numberof organisations and individuals were particularly asked togive their views on the subject and, where received, thesewere also carefully considered. A list of those organisationsand individuals who contributed information and expressedviews is given in Appendix H.

1.3.3 Reforming the Task Group in 1998Although the original 1994 Guide was successful in focusingdiverse professional interests towards common guidelines fordealing with subsidence, heave and landslip, there have beensince publication numerous developments in procedures andlegislation which have highlighted the need to bring it up todate. In particular the 1994 Guide was not thought to givesufficient guidance on trees and tree management.

It was therefore decided in 1998 to reform the Task Group,this time including arboriculturists, not only to amend andupdate the Guide, but also to write an entire chapter (Chapter 8)devoted to trees and tree management.

Finally, although the 1994 Guide was intended to reassureValuers and homeowners that minor cracking was of littleconsequence structurally and should not affect property val-

ues, over-caution on the part of Valuers and property ownersremains. Insurance claims are increasingly being made as aresult of this type of damage even though most Experts wouldregard the damage as being the natural consequence of nor-mal movement in low-rise buildings. As a result, furtherattempts have been made in the new Guide to define this typeof damage and movement more precisely with a view tobringing a greater degree of understanding and realism intothe assessment of damage to low-rise buildings.

1.4 Customer care

Where a property is insured for subsidence and indeed otherbuilding fabric damage risks, the relationship between the

Insured (the property owner) and the Insurer of the property isan important one. Chapter 4 deals in detail with insurancematters, but it is worth stating here the fundamentals of thisrelationship. It is one based upon mutual trust. The two par-

ties enter into a contract, usually an annually renewable one,whereby the Insured agrees to maintain the property in a rea-sonable state of repair and pay an annual premium to theInsurer for cover against the possibility of certain statedevents causing significant damage to the property one beingsubsidence. If any of these events unfortunately occur, thenthe lay Insured naturally believes that the Insurer will solvethe problem, often without really appreciating the preciseterms of the insurance contract between the two parties. It is afact that most Insurers are perceived by householders as offer-ing exactly the same quality of cover and all are assumed tobe reputable if anything they are thought to vary only on thepremium they charge.

In the case of domestic property the relationship is rarelyone between equals. Invariably, when a claim occurs, theInsurer is in a more influential position than the Insured.Insurers know much more about legal, technical and insur-ance matters than their customer the Insured. Building dam-age claims, such as subsidence, are usually very traumaticexperiences for householders.

It is therefore important for Insurers to remember that asalways, customer care is of paramount importance in thisrelationship, as between the fair Insurer and the honestInsured. Recommendations for good practice are given inSection 3.2

1.5 The Expert

Readers of the Guide will note that reference is madethroughout the document to the professional TechnicalExpert Adviser (The Expert) (see 2.2.3). This is a deliberatedecision in order that the Guide will not be seen as preferringone type of professional adviser to another.

The most important criterion is the experience of theExperts rather than their professional qualifications. Clearlysome professions are more likely to have the appropriateexperience than others but it is recommended that this be amatter to be decided in each individual case (see 2.2.3).

1.6 Codes of Practice, Standards andRegulations, etc.

Where reference is made in the text to such documents, therelevant versions are those current at the time of publicationof this Guide. Such documents, however, are regularlyrevised and reference should always be made to the editioncurrent at the relevant time. Likewise, this Guide reflects cur-rent practice at the date of publication of it and referenceshould always be made to an Expert for guidance on currentgood practice.


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Chapter 2

Explanation of terms

2.1 Introduction 18

2.2 Terms 18

2.2.1 Technical terms 18

2.2.2 Insurance terms 19

2.2.3 The technical expert adviser (The Expert) 20

2.2.4 Glossary of qualifying bodies for Experts 21

2.3 Mortgage procedure the relationship between Lenders,

Borrowers, Insurers and Valuers 21

2.3.1 The mortgage 21

2.3.2 The role of the valuer 21

2.3.3 Insurance arrangements 222.3.4 Standard house purchase reports 22

2.4 Supplementary reports 23


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2.1 Introduction

Over the past 20 years, efforts have been made by interestedparties, including Engineers, Insurers, Lenders, Lawyers andSurveyors, to define subsidence and heave and to distinguishthem from settlement and other forms of movement in build-

ings. It has been generally agreed that there is a distinction.This Chapter attempts to explain these and other terms com-monly used when dealing with building damage.

These explanations have been derived from the attempts byothers to define the terms. The terms given below are nowbelieved to be commonly accepted but they are for generalguidance only. It should be emphasised that these are notlegally binding definitions and reference must be made to theterms of individual insurance policies which may use differ-ent definitions. It is still the case that some professional prac-titioners and groups define terms differently from those givenbelow. It is therefore important to establish whether there isany difference in understanding of the terms used.

The insured events within the scope of this report are subsi-dence, heave and landslip. In establishing whether damage

has been caused by one of these insured perils, carefulthought needs to be given to whether there has been someother factor, or combination of factors, which could havecaused the damage to the building, such as roof spread, lintelfailure or thermal movement.

2.2 Terms

2.2.1 Technical terms

SettlementFor insurance purposes settlement is defined as movementwithin a structure due to the distribution or redistribution ofloading and stresses within the various elements of construc-tion. This normally occurs in the early stages of the life of abuilding and may be associated with the initial compaction,consolidation, or movement in, the ground beneath the foun-dations due to the weight of the building. This initial settle-ment is not an insured peril.

Cracking caused by this initial settlement is not normally acontinuing problem. The cause of cracking and distortionoccurring later in the life of the building, which may requireremedial work, must be identified. Should initial settlementresult in major structural damage, this would normally bedealt with under the terms of an NHBC warranty or equiva-lent.

SubsidenceFor insurance purposes subsidence (see Figs. 2.1 and 2.2) isdefined as the downward movement of a building and itsfoundation caused by loss of support of the site beneath thefoundations. This is usually associated with volumetricchanges in the ground supporting the foundations, e.g.:

compression of peat, other than that due directly to theself-weight of the building

further compaction or consolidation of fill shrinkage or softening of clay soils washing away of fines in granular material

It should be emphasised that all these volumetric changes tothe ground can only occur as a direct result of an external fac-tor, e.g:

change in ground water level leaking drains influence of trees or other vegetation

mining decomposition of organic material extremes of climate change adjacent excavations

If subsidence is uniform throughout the foundations thenmajor damage in the superstructure of the building is unlike-ly. However, if differential subsidence occurs, remedial mea-sures to stabilise the foundations and to repair damage, maybe required to bring the movement within acceptable limits.

As well as the principal downward movement, there canoccasionally be some lateral movement of the ground.

The principal test to distinguish between subsidence or set-tlement of the site is to establish whether the downwardmovement of the ground would have occurred, at least tosome extent, with no applied load from the building. If move-ment of the site would have occurred without the appliedload, then damage is a result of subsidence.

HeaveHeave (see Fig. 2.3) is the volumetric expansion of theground beneath part or all of the building. This is normallytaken to mean upwards movement of the site caused byexpansion or swelling of the subsoil. This can result from anumber of causes such as:

moisture increase in clay soils, e.g. from leaking drainsor the removal or reduction of water uptake of trees.

removal of or significant reduction in load frost

2 Explanation of terms

Fig. 2.1 Idealised subsidence movement patterns

Fig. 2.2 Typical actual subsidence crack patterns

Fig. 2.3 Typical heave patterns


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Heave recoveryHeave recovery is the whole or partial reversal of previoussubsidence and may not necessarily be detrimental to the sta-bility of the property (see section 8.5).

LandslipLandslip (see Fig. 2.4) is the sudden movement of soil on aslope, or gradual creep of a slope over a period of time.

Damage thresholdThis is the borderline which divides damage which is incon-

sequential and unlikely to be of concern from that which islikely to be of concern, particularly to Valuers at point of saleand to property owners generally. For property owners, theacceptability or otherwise of damage is often a subjectivematter. However, Valuers and other professionals whoappraise properties, need to be more objective otherwiseproperties with very minor inconsequential cracks could bemarked down in value or could be the subject of unneces-sary insurance claims.

There is no universal agreement on what constitutes anacceptable damage threshold, since much will depend onissues such as the property type and construction, soil typesand presence of vegetation. However, it is probably fair to saythat a crack in a property which is 2mm or less in width andwhich does not vary by more than 1mm in width during the

course of an annual seasonal cycle of ground movements,atmospheric and temperature changes, may be regarded asinconsequential. However, a number of cracks of lesser widthmay be a cause for concern. Hairline crack widths up to0.25mm can for all practical purposes be ignored.

2.2.2 Insurance termsIt is important when considering the points made under thisheading to bear in mind the comments in Chapter 4.

The siteIn most cases, insurance policies cover subsidence of the siteand this is generally considered by the Insurance Ombudsmanto be the prepared ground on which the building is erected

after the foundation trenches have been dug and immediatelyprior to the construction of the building. This means thatsome Insurers may also give cover for subsidence resultingfrom defectively compacted fill beneath the building founda-tion.

Some Insurers use the term land belonging to the build-ing. This probably means adjacent gardens, driveways,patios, etc. as well as the ground directly below the property.This highlights that there can be important differencesbetween policy wordings and their interpretation, and theInsured should always establish what cover they have withthe Insurer concerned. Insurers, however, should try to avoid

subtle differences of wording which only serve to confuse thepublic and those charged with administering claims.

Sum insuredThis is the sum which the owner (the Insured) declares thatthe whole of the insured property will cost to rebuild. Thewhole property is normally defined as all the structures builton the site, i.e:

house detached/attached garage

outbuildings swimming pools and tennis courts drives, paths, garden and/or retaining walls, patios,

fences

It does not include the value of the ground within the bound-aries of the site. It is usually calculated by multiplying thetotal area of all floors of the house by a basic cost per unitarea, with the figures commonly used nowadays being thosepublished annually by the RICS Building Cost InformationService. Some Insurers also require above average quality fit-ments in a property to be taken into account, e.g:

double glazed windows high quality kitchens

high quality bathroom and bedroom fitments

The figure should also include the cost of employing a profes-sional building advisor, e.g. Architect or Surveyor, to assistwith the administration of the rebuilding contract and thisnormally adds about a further 15% to the basic rebuildingsum to make up the full sum insured. The RICS figures auto-matically include an amount for professional fees as well ascosts incurred in demolition and site clearance where neces-sary.

Policy conditionsThese are the general conditions applicable to the whole poli-cy, and are set out in the policy booklet issued to house own-ers by their Insurers. They deal with the way the policy must

be administered by both the Insured and Insurer; if they arenot complied with, Insurers may be able to avoid liabilityunder the policy.

Claims conditionsThese conditions set out what needs to be done by an Insuredwhen a claim is made under the policy. They also explainwhat rights the Insurer has in dealing with a claim such asseeking payments from other parties who might have beenresponsible for the damage, or getting a contributory paymentfrom another Insurer who might also have been providingcover.

Fig. 2.4 Landslip


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ExclusionsThese may be exclusions which apply to the whole policy,e.g.:

radioactive contamination war risks damage from sonic bangs

However there are usually specific exclusions too, whichrelate to particular sections of the policy, e.g. the BuildingsSection. For example, any of the following will probably beexcluded from cover provided for subsidence, heave andlandslip:

damage resulting from demolition damage caused by structural repairs or alterations to

buildings the insurance excess which is the first part of the cost of

claim born by the Insured faulty or poor workmanship see below defective design the use of faulty materials in the buildings

The normal exclusions for faulty or poor workmanship,defective design and the use of faulty materials in the build-

ings, if taken literally, would enable Insurers to avoid the vastmajority of subsidence claims under their policies. For exam-ple, if a building does subside then the chances are that theworkmanship, design or materials have proved inadequate insome way albeit that the building may be many years old andhas shown no previous signs of movement. The intentiontherefore is to only apply the exclusions where these are thesole cause of the damage, i.e. without an intervening event,such as the activities of tree roots, leaking drains, or move-ment for some reason in the sub strata.

Complaints proceduresIn the event of a complaint needing to be made about a claim,the Insured will normally be asked to follow the procedureoutlined below:

Refer the case in the first instance to the senior manage-ment of any firm of technical professional advisersinvolved, i.e. engineers or loss adjusters (see 2.2.3),before writing to the Insurer or Lender.

If the complaint is not satisfied, write to the manager ofthe handling office of the insurance company.

If the complainant is still not satisfied, they should writeto the Head Office of the insurance company for theattention of the Chief Executive.

If the problem still cannot be resolved, write to theInsurance Ombudsman Bureau or Personal InsuranceArbitrator, if the Insurer belongs to one of these. Bothschemes relate only to personal insurance and not tocommercial insurance contracts, but in approaching them

an Insureds normal legal rights are not affected in anyway.

2.2.3 The technical expert adviser (The Expert)The investigation and rectification of subsidence damage caninvolve many specialist advisers. However, it is important forthe owner of the property (and probably also the Insurer ofthe property) that a single party should have overall technicaland managerial responsibility for seeing the matter throughfrom the initial identification of damage through to the issu-ing of a Final Report to the Insured and/or a Certificate ofStructural Adequacy. Such a technical expert adviser isreferred to in this document as the Expert. The responsibilityof the Expert is to be familiar with all aspects of a subsidenceproblem. For details of relevant professional bodies see 2.2.4.

The Expert is obliged to demonstrate reasonable skill andcare to be expected of an Expert advising on the type of workfor which they have been engaged by the client.

The Expert is normally required at three stages:

initial appraisal (see Chapter 6) further investigation (see Chapter 7) remedial works (see Chapters 8, 9 and 10)

Experts engaged to advise on subsidence and heave, particu-larly in assessing whether remedial works may or may not beneeded, should have detailed knowledge of building construc-tion and be experienced in investigating and appraising subsi-dence and any resultant damage. An Expert may be any oneof the professionals described below, but should be capable ofappraising and accepting responsibility for advising uponsome or all of the following:

scope of investigation required building design and construction foundation design ground engineering recognition of the severity and relevance of damage to

buildings design and/or specification of remedial works, including

site inspections during the execution of them giving an assurance in writing, upon completion of reme-

dial work, that the work has been properly undertaken inthe form of a Final Report to the Insured and/or aCertificate of Structural Adequacy. The assurance should

not rely solely on a guarantee or warranty issued by aContractor if required, recommend the appointment of an arboricul-

turist to advise on trees, tree physiology and water use the overall project management.

Experts will be concerned in establishing the cause of thedamage or structural movement by detailed technical investi-gation involving examination and measurement of the build-ing and the damage as well as instigation of any requiredgeotechnical examinations of the ground on which the proper-ty stands. They should be capable of interpreting the results ofthose investigations and thus be able to distinguish betweenthe effects and symptoms of subsidence and heave and otherpossible causes of structural damage or movement. Experts

should also have appropriate Professional IndemnityInsurance.

The Expert can be directly appointed by an Insurer, or alter-natively indirectly via a Loss Adjuster. Experts appointeddirectly by Insurers are usually specialist consultants or alter-natively Loss Adjusters who have in-house technical expertadvisers.

Where an Insurer appoints a Loss Adjuster to investigate asubsidence claim, if the Loss Adjuster does not have in-houseappropriately qualified staff, they may employ the services ofan external specialist consultant, usually on a panel basis. Inthis case, the Loss Adjusters Expert should still be requiredto fulfil the functions listed above, including on completion,the issue of a Certificate of Structural Adequacy, if requiredto do so.

Most Insurers will take on the responsibility of appointingExperts but some Insurers will ask their Insured to do this. Itis nevertheless very important that, in principle, before anyExpert is appointed by an Insured and investigations started,the Insurer concerned is told about the damage.

If the Insured does not already know of an appropriateExpert, then names of professionally qualified Experts cannormally be given to enquirers by the relevant professionalinstitutions. The Insured should be satisfied that the Experthas the appropriate experience and is prepared to act in accor-dance with the relevant terms listed above prior to beingappointed.

The types of professional advisers who may be able to acteither as Experts or in support of Experts are considered inthe following paragraphs. It should be noted that these advis-ers could all be employed by the same firm.

Chartered and Incorporated EngineersMembers of the Institution of Structural Engineers (IStructE)


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or the Institution of Civil Engineers (ICE) have the mostappropriate qualifications to conduct both the initial appraisalas well as any subsequent further detailed investigation. Thelatter requires a much greater technical expertise which isnormally only possessed by appropriately experiencedStructural Engineers, who may be employed by a firm of con-sultants or loss adjusters.

Members of the IStructE cover a wide range of expertise sonot all necessarily have the relevant expertise and experienceto comment on foundation failure of low-rise buildings andon the implications of subsidence damage generally.

The majority of Insurers prefer to engage Engineers withthe relevant experience for initial appraisals, further investi-gations and property stabilisation, including underpinning ifrequired. Engineers can also be used for specifying and super-vising above ground repair works.

Chartered and Incorporated Surveyors and BuildersAs with Engineers, there are many disciplines within the sur-veying profession and, again, not all will have the appropriatebackground to carry out an initial appraisal. For instance,Chartered Building Surveyors qualified within the RoyalInstitution of Chartered Surveyors are likely to be more suit-able than Valuation, Fine Art or Quantity Surveyors of thesame Institution, although all may appear to have the same

qualifications on paper.As an alternative to using Engineers, Chartered BuildingSurveyors and Chartered Builders may be used to specify andsupervise above-ground repair works. Chartered BuildingSurveyors also have a role to play in connection with partywall legislation (see 10.3.5)

ArboriculturistsIn cases involving assessment of the effects of trees on build-ings or requiring remedial action to trees, it will probably benecessary to consult a tree specialist. These specialists shouldbe qualified arboriculturists who are normally members of arelevant professional association, which are given in 2.2.4.

Loss Adjusters

These are professional advisers appointed by insurance com-panies to advise impartially on the relevance of the claimwithin the terms of the policy. They are required to:

investigate, quantify and administer the claim as quicklyand efficiently as possible in accordance with the termsof the policy, and to try to avoid delays

present the views of the Insured impartially to theInsurer, even if they are not in agreement with thoseviews.

Unless the Loss Adjuster is a Chartered Engineer or BuildingSurveyor, they are unlikely to handle the technical aspects ofa subsidence claim and will advise on insurance matters only,referring all technical matters to in-house or external

Engineers and Surveyors.Some Insurers may choose not to appoint an Adjuster but

may decide to administer the claim themselves and use aConsulting Engineer to advise directly on the technicalaspects.

Local Authority technical officersThese, including Building Control Officers and Public HealthInspectors, have appropriate experience but their terms ofemployment restrict them to ensuring compliance with cur-rent legislation. They will normally refer the enquirer to oneof the parties listed. The important point is to ensure thatthose who do advise have the necessary experience.

Loss AssessorsLoss Assessors are not normally associated with subsidenceclaims because of the technical issues involved but whereengaged by the Insured to assist in the making of a claim,their fees would be met solely by the Insured.

ArchitectsA small number of Architects do have sufficient experienceof subsidence and heave matters to be able to undertake theinitial appraisal, but the vast majority do not. Architects aregenerally not employed on subsidence claims unless substan-tial rebuilding of a property is involved.

OthersIt should be emphasised that a lack of formal qualificationsmay not necessarily prevent an individual carrying out the ini-tial appraisal if they have the relevant experience, but it can-not be emphasised too strongly that care should always beexercised when appointing an Expert to ensure that they canidentify and appraise subsidence and heave damage, and dis-tinguish it from other types of building/structural movementor damage.

2.2.4 Qualifying bodies for Experts The Institution of Structural Engineers The Institution of Civil Engineers The Royal Institution of Chartered Surveyors The Chartered Institute of Builders The Arboricultural Association The National, London and Regional Tree Officers

Associations

2.3 Mortgage procedure the relationshipbetween Lenders, Borrowers, Insurers andValuers

2.3.1 The mortgageA Mortgage Deed is an agreement between a Lender and aBorrower usually in connection with a loan for a particularproperty purchase.

The Lender agrees to provide a sum of money to theBorrower usually to be used in the purchase of a property inreturn for a promise by the Borrower to repay the loan, withinterest over the agreed mortgage term, often 25 years. Therewill be other agreed terms and conditions including methodsof repayment, the necessity to insure the buildings, the needto keep the property in good repair, a requirement to notifythe Lender of any works which might affect the value of theproperty and the procedure if the Borrower defaults on repay-ments. All these items will be contained in a legal documentknown as a Mortgage Deed. Where a mortgage is given, theLender has an interest in the property because it is the collat-eral or security for the loan, but has no right of interferencewith the purchasers rights as owner unless there is a failureto comply with the terms of the Mortgage Deed.

The existence of the mortgage is entered on the ChargesRegister at the Land Registry against the address of the prop-

erty. The Borrower (owner) cannot therefore dispose of theproperty by selling it without the prospective purchaser beingaware that there is a legal charge over the property and hencethe Borrower does not have an unencumbered right to sell it.

During the course of the sale of a property, the vendor isnormally required to complete a standard Law SocietyPreliminary Enquiries form about the property for the benefitof the purchaser. This form requires the vendor to state(amongst other matters) whether the property has, to the bestof their knowledge, suffered from subsidence, heave or land-slip.

2.3.2 The role of the ValuerLenders will usually obtain a valuation on a property beingconsidered for a mortgage loan. A Valuer reporting to aLender will almost always be professionally qualified, beingeither a member of the Royal Institution of CharteredSurveyors or of the Incorporated Society of Valuers andAuctioneers. The Valuer will be expected to have knowledge


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and experience in the local geographical area in which valua-tions are carried out and to work within the Practice/Guidance

Notes for Valuers produced by the two professional bodiesmentioned above, subject to any specific requirements of theparticular Lender. Typically the Valuer will:

inspect the property, including factors such as its locationand condition, which could have a significant effect onthe market value

advise the Lender of the open market value. This willinvolve obtaining as much sales evidence as is availableregarding transactions in similar properties in the periodimmediately preceding the inspection. The analysis ofthis will assist in reaching an opinion on the appropriatevaluation after taking all factors into account

provide an opinion on the estimated current reinstatementcost of the building for insurance purposes. This willinclude any garages and outbuildings with the cost of thesite clearance and professional fees. In reaching this sum,the Valuer will normally have regard to the figures pro-duced annually by the Building Cost Information Serviceof the Royal Institution of Chartered Surveyors. Thesecover a wide spectrum of properties in different parts ofthe country and of different ages and quality. This topicis dealt with under 2.2.2.

In all these obligations, the Valuers duty is to the Lender.However, where the Valuer knows that the prospective pur-chaser is relying on the report, the Valuer may also have aduty of care to the prospective purchaser. This duty of carewill relate to the same services which the Valuer was instruct-ed to provide to the Lender and only to those services. Thismay include the reporting of major factors which are, orought to be, obvious in the course of a reasonably profession-al visual inspection where these are likely materially to affectthe value of the property.

Only Valuers are expert in marketability and value. If doubtexists, or if there are circumstances where the value of theproperty is likely to be reduced, the advice of a ValuationSurveyor should be sought.

2.3.3 Insurance arrangementsA Lender making a mortgage loan will require the propertytaken as security to be insured and for the perils covered toinclude subsidence, heave and landslip. In recent yearsInsurers have encouraged Lenders to take a greater role inevaluating structural movement insurance risks on theirbehalf. As a consequence, many Lenders have arrangementswith Insurers whereby properties are automatically taken onrisk by the Insurer without the need for individual cases to beproposed to them unless specified circumstances exist.Examples of specified circumstances would be where a prop-erty is affected by movement which appears to be continuing,or where there are circumstances which represent a risk ofmovement in the future, such as trees on shrinkable soils

which are close to or within influencing distance of the prop-erty. In these cases, the Insurer may wish to consider thedetails prior to deciding whether or not to provide cover forthe property.

In implementing these arrangements, Lenders will usuallyrequire their Valuers reports to contain clear statements(often using standard phrases) as to whether any identifiedmovement is considered to be continuing or long-standing/non-progressive, or as to future risk if this is thoughtto exist. Prospective Borrowers who are arranging insurancethemselves rather than through the Lender, and who havebeen supplied with a copy of the Valuers report, are likely touse the Valuers comments when completing the InsuranceProposal Forms. Alternatively Borrowers would be advised toobtain their own report if continuing movement had beenidentified.

Whilst structural movement requires special care both inassessment and resulting recommendations, it is important toremember that a Valuer is expected to make a snapshot

judgment based only on a limited inspection. If it is obviousthat movement has cease

subsidance in low rise buildings (2)

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