Has Your House Got Cracks

by Freeman, T. J.; Driscoll, R. M. C.; Littlejohn, G. S.

• ISBN13: 9780727730893
• ISBN10: 0727730894
• Edition: 2nd
• Format: Paperback
• Copyright: 2003-03-01
• Publisher: Inst of Civil Engineers Pub

Summary

This guide was commissioned by the Institution of Civil Engineers and the Building Research Establishment to provide practical guidance for homeowners whose properties have been affected by subsidence, or heave, or who are concerned by the potential risk of damage. The first, best-selling, edition dealt specifically with the problems associated with properties founded on shrinkable clay soils, and was reprinted many times. The second edition has been expanded to include sections on other types of subsidence and causes of damage that are unrelated to foundation movement. It also looks at the potential problems that can arise when buying or selling a property that has previously been affected by subsidence.

Table of Contents

FREQUENTLY ASKED QUESTIONS	1	(82)
1. INTRODUCTION	7	(7)
Background	7	(1)
Recent trends in subsidence claims	7	(3)
Changing attitudes towards subsidence and heave damage	10	(1)
Insurance cover	11	(3)
What is covered?	11	(2)
Geographical loading	13	(1)
2. CAUSES OF CRACKING	14	(6)
Physical changes	14	(2)
Seasonal temperature and humidity	14	(1)
Initial drying	15	(1)
Loss of volatiles	15	(1)
Freezing and thawing of water	15	(1)
Efflorescence	15	(1)
Chemical changes	16	(1)
Moisture expansion of brickwork	16	(1)
Sulfate attack	16	(1)
Corrosion or oxidisation of steel	17	(1)
Other chemical processes	17	(1)
Over-stressing	17	(1)
Vibration	18	(1)
Wear and tear	18	(2)
3. CAUSES OF SUBSIDENCE AND HEAVE	20	(13)
Erosion	21	(1)
Shrinkage or swelling in the surface soil	21	(12)
Why clay soils shrink and swell	22	(1)
Characteristic properties	22	(1)
Liquid and plastic limits	23	(1)
Where are shrinkable clays found?	23	(1)
Shrinkage potential	24	(1)
Desiccation	25	(1)
How much desiccation?	25	(1)
Effect of trees	26	(2)
Effect of climate	28	(3)
Effect of surroundings	31	(2)
4. HOW YOUR HOUSE IS BUILT	33	(8)
Foundations	33	(4)
Alternative forms of foundation	36	(1)
Floors	37	(1)
Walls	37	(4)
5. PREVENTING DAMAGE	41	(3)
Tree management	41	(1)
Structural alterations	41	(1)
Landscaping	42	(1)
Excavation	42	(1)
Drainage	42	(2)
6. SUBSIDENCE TO A NEIGHBOURING PROPERTY	44	(4)
Has my own property been affected?	44	(1)
Will I be affected by the remedial works?	45	(1)
Are the trees in my garden the cause of the problem?	46	(2)
7. RECOGNISING SUBSIDENCE DAMAGE	48	(13)
Have the foundations moved?	49	(6)
Assessing the damage	50	(2)
Appearance	52	(1)
Location	53	(2)
Timing	55	(1)
Other indications	55	(1)
Cause for concern?	55	(3)
Is stability threatened?	55	(2)
Is there a threat to safety?	57	(1)
Is serviceability affected?	57	(1)
Will I be able to sell the house?	57	(1)
Aesthetics	58	(1)
What should I do?	58	(3)
8. MAKING A CLAIM	61	(7)
Professional advice	62	(2)
Loss adjuster	62	(1)
Building surveyor	63	(1)
Structural engineer	63	(1)
Civil engineer	63	(1)
Appointing the investigator	64	(1)
Project management	65	(1)
What to expect	66	(2)
9. THE INVESTIGATION	68	(15)
Initial investigation	69	(5)
Visual inspection	69	(1)
Distortion survey	70	(2)
Desk study	72	(1)
Trial pits	73	(1)
Drain survey	73	(1)
What caused the movement?	74	(3)
Engineer's Report	77	(1)
Borehole investigations	78	(2)
Things to look out for	80	(3)
10. MONITORING	83	(11)
What is monitoring?	83	(1)
Monitoring to confirm that cause of damage is not subsidence	84	(1)
Monitoring to establish cause of subsidence	84	(1)
Monitoring to measure rate of movement	84	(1)
Monitoring to check success of remedial action	84	(1)
Crack width monitoring	84	(6)
Steel rule	85	(1)
Magnifier and graticule	85	(1)
Glass tell-tales	85	(1)
Plastic tell-tales	86	(1)
Demec points	87	(1)
Brass screws	88	(1)
Interpreting crack measurements	88	(2)
Level monitoring	90	(2)
Interpreting level measurements	90	(2)
Monitoring lateral movement	92	(1)
Observation period	92	(2)
11. THE SOLUTION	94	(9)
Repairing or strengthening the superstructure	94	(1)
Drainage repairs	94	(3)
Reducing the influence of trees	97	(4)
Tree removal	98	(2)
Tree pruning	100	(1)
Root pruning	100	(1)
Root barriers	101	(1)
Soil stabilisation	101	(1)
Remedial underpinning	101	(2)
12. DOES MY HOUSE NEED TO BE UNDERPINNED?	103	(4)
Criteria for underpinning	103	(3)
Is structural stability threatened?	103	(1)
Is movement continuing?	104	(1)
Is the movement excessive?	104	(2)
What is the cost?	106	(1)
Is underpinning needed?	106	(1)
13. DIFFERENT TYPES OF UNDERPINNING	107	(9)
Mass concrete	107	(2)
Pier-and-beam	109	(1)
Pile-and-beam and piled-raft	109	(4)
Mini-piling	113	(1)
Partial underpinning	113	(3)
14. HAVING THE WORK DONE	116	(8)
The specification	116	(1)
The contract	117	(2)
Cash settlement	119	(1)
Party wall awards	120	(1)
Will I have to move?	120	(1)
Payment	121	(1)
Supervision	121	(1)
Building Regulations	122	(1)
Warranties	122	(2)
15. WHAT IF THINGS GO WRONG?	124	(2)
During the investigation	124	(1)
During the contract	125	(1)
After completion	125	(1)
16. BUYING AND SELLING	126	(15)
Surveys	126	(2)
Engineer's Report	128	(1)
What to look out for when buying a house	128	(8)
Distortion	128	(6)
Signs of subsidence	134	(2)
Considerations for the seller	136	(5)
Checking for signs of damage	136	(1)
Selling after damage has been reported to insurers	137	(1)
Will a claim for subsidence damage make it difficult when I come to sell?	138	(2)
Certificate of Structural Adequacy	140	(1)
Non-disclosure	140	(1)
REFERENCES	141	(2)
APPENDIX A: GLOSSARY OF TECHNICAL TERMS	143	(5)
APPENDIX B: RELEVANT ORGANISATIONS	148	(3)
APPENDIX C: FOUNDATION AND SUPERSTRUCTURE DESIGN	151