Has Your House Got Cracks? A homeowner’s guide to subsidence and heave damage, Second edition

Contents

FREQUENTLY ASKED QUESTIONS 1

1. INTRODUCTION 7
Background 7
Recent trends in subsidence claims 7
Changing attitudes towards subsidence and heave damage 10
Insurance cover 11
What is covered? 11
Geographical loading 13

2. CAUSES OF CRACKING 14
Physical changes 14
Seasonal temperature and humidity 14
Initial drying 15
Loss of volatiles 15
Freezing and thawing of water 15
Efflorescence 15
Chemical Changes 16
Moisture expansion of brickwork 16
Sulfate attack 16
Corrosion or oxidisation of steel 17
Other chemical processes 17
Over-stressing 17
Vibration 18
Wear and tear 18

3. CAUSES OF SUBSIDENCE AND HEAVE 20
Erosion 21
Shrinkage or swelling in the surface sol 21
Why clay soils shrink and swell 22
Characteristic properties 22
Liquid and plastic limits 23
Where are shrinkable clays found? 23
Shrinkage potential 24
Desiccation 25
How much desiccation? 25
Effect of trees 26
Effect of climate 28
Effect of surroundings 31

4. HOW YOUR HOUSE IS BUILT 33
Foundations 33
Alternative forms of foundation 36
Floors 37
Walls 37

5. PREVENTING DAMAGE 41
Tree management 41
Structural alterations 41
Landscaping 42
Excavation 42
Drainage 42

6. SUBSIDENCE TO A NEIGHBOURING PROPERTY 44
Has my own property been affected? 44
Will I be affected by the remedial works? 45
Are the trees in my garden the cause of the problem? 46

7. RECOGNISING SUBSIDENCE DAMAGE 48
Have the foundations moved? 49
Assessing the damage 50
Appearance 52
Location 53
Timing 55
Other indications 55
Cause for concern? 55
Is stability threatened? 55
Is there a threat to safety? 57
Is serviceability affected? 57
Will I be able to sell the house? 57
Aesthetics 58
What should I do? 58

8. MAKING A CLAIM 61
Professional advise 62
Loss adjuster 62
Building surveyor 63
Structural engineer 63
Civil engineer 63
Appointing the investigator 64
Project management 65
What to expect 66

9. THE INVESTIGATION 68
Initial investigation 69
Visual inspection 69
Distortion survey 70
Desk study 72
Trial pits 73
Drain survey 73
What cause the movement? 74
Engineer’s Report 77
Borehole investigations 78
Things to look out for 80

10. MONITORING 83
What is monitoring? 83
Monitoring to confirm that cause of damage is not
subsidence 84
Monitoring to establish cause of subsidence 84
Monitoring to measure rate of movement 84
Monitoring to check success of remedial action 84
Crack width monitoring 84
Steel rule 85
Magnifier and graticule 85
Glass tell-tales 85
Plastic tell-tales 86
Demec points 87
Brass screws 88
Interpreting crack measurements 88
Level monitoring 90
Interpreting level measurements 90
Monitoring lateral movement 92
Observation period 92

11. THE SOLUTION 94
Repairing or strengthening the superstructures 94
Drainage repairs 94
Reducing the influence of trees 97
Tree removal 98
Tree pruning 100
Root pruning 100
Root barriers 101
Soil stabilisation 101
Remedial underpinning 101

12. DOES MY HOUSE NEED TO BE UNDERPINNED? 103
Criteria for underpinning 103
Is structural stability threatened? 103
Is movement continuing? 104
Is the movement excessive? 104
What is the cost? 106
Is underpinning needed? 106

13. DIFFERENT TYPES OF UNDERPINNING 107
Mass concrete 107
Pier-and-beam 109
Pile-and-beam and piled-raft 109
Mini-piling 113
Partial underpinning 113

14. HAVING THE WORK DONE 116
The specification 116
The contract 117
Cash settlement 119
Party wall awards 120
Will I have to move? 120
Payment 121
Supervision 121
Building Regulations 122
Warranties 122

15. WHAT IF THINGS GO WRONG? 124
During the investigation 124
During the contract 125
After completion 125

16. BUYING AND SELLING 126
Surveys 126
Engineer’s Report 128
What to look out for when buying a house 128
Distortion 128
Signs of subsidence 134
Considerations for the seller 136
Checking for signs of damage 136
Selling after damage has been reported to insurers 137
Will a claim for subsidence damage make it difficult
when I come to sell? 138
Certificate of Structural Adequacy 140
Non-disclosure 140

REFERENCES 141

APPENDIX A: GLOSSARY OF TECHNICAL TERMS 143

APPENDIX B: RELEVANT ORGANISATIONS 148

APPENDIX C: FOUNDATION AND SUPERSTRUCTURE
DESIGN 151