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NHBC Buildmark Warranty
Management of Ground Risk
John Jones NHBC Engineering Manager
NHBC - Past
Established in 1936
Mission to Raise Standards
Private company limited by
guarantee
No shareholders & non profit
distributing
10 year warranty in 1968
NHBC - Present
80%+ warranty market share
Buildmark, Choice & SOLO
c65% Building Control in E & W
8M homes covered
c£70M pa in claims costs
1200 staff - 50% technical
The Virtuous Circle
Customers
c15,000 registered builders
1.7M homeowners
112,000 polices in 13/14?
Section 3 Claims Volumes 2011/12
56 293
2530
5723
254
203796
£0
£5,000
£10,000
£15,000
£20,000
£25,000
£30,000
£35,000
£40,000
£45,000
£50,000
2009 2010 2011 2012
Other
Ancillary Buildings and External Works
Services, Fixtures and
Finishes
Roofs
Superstructure
Substructure and Ground Floors
Foundations
Circa 10,000 in total
Section 3 Claims Costs 2011/12
£9.1
£6.8
£12.4
£14.2
£0.4£0.5 £1.8
£0
£5,000
£10,000
£15,000
£20,000
£25,000
£30,000
£35,000
£40,000
£45,000
£50,000
2009 2010 2011 2012
Other
Ancillary Buildings and External Works
Services, Fixtures and
Finishes
Roofs
Superstructure
Substructure and Ground Floors
Foundations£45.2m in total
Risk Management
Brownfield developments
Marginal sites
MMC’s
New Products
Mineral safeguarding
Risk Management
Risk Management - Standards
NHBC Standards
NHBC Requirements
Performance Standards
Guidance on meeting
performance
Risk Management
Raising Standards
Protecting Homeowners
Protecting Builders – Liability in years 1 & 2
Mitigating Buildmark claims – NHBC liability years
3-10
Risk Management - why
Prevent foundation failures
££££££’s repair costs
Disruption to homeowners
Reputation
MARGINAL SITE – POOR GROUND CONDITIONS
MARGINAL SITE – POOR GROUND CONDITIONS
CH 4.2 SITE – NO HEAVE PRECAUTIONS
CH 4.2 SITE – SUBSIDENCE
CH 4.2 SITE?
MARGINAL SITE – POOR GROUND CONDITIONS
37 No 2 storey plots – mixed types
Soils – soft/firm clay to 1.6m, peat 1.6m to 3.1m,
soft/firm clay 3.1m to 3.8m, firm/stiff gravelly clay
below 3.8m
Site raised by 1m to 2.5m above original levels
Settlements - 186mm to 329mm predicted
Surcharging of 4m to 5.5m required
Risks
Poor ground conditions/soils
Low strength & bearing capacity
Large settlements of buildings
Differential settlements of buildings
Differential settlements between building and
external works
Inadequate ground treatment/remediation
So where does the lime come in?
Construction Uses
Modification of poor cohesive /waterlogged soils
Optimum conditions for compaction
Improved strength/bearing capacity
Reduced settlements
Maturing technology /process?
Working platforms/piling mats
Roads, car parking, commercial developments
Reported benefits
Costs savings
Time savings
Environmental impact
Reduced waste generation
Landfill taxes
Sustainability
NHBC current position Limited track record in UK
housebuilding
Use on marginal sites
Panacea for poor sites?
Sustainability
Has its place in the industry in
correct situations
Long term performance > 60 years
Our experiences
Increase in proposals for ‘soil stabilisation’ including partials
depth treatments and engineered fills up to 8m deep
Fill/made ground being classified as ‘natural’ or reworked
natural soils
Lack of adequate independent site investigation
Minimal initial classification of soils
Few trial mixes and partial depth treatments
Method rather than End Product specifications
Inadequate verification after treatment
Our expectations
Adequate initial site investigations (independent)
Establishing site specific suitability
Adequate initial classification of soils, testing and trial mixes
Post completion verification (laboratory and on site)
Assessing load/settlement characteristics – treated material
and/or underlying soils
Appropriate substructure/foundation solutions
Durable long term performance (60+ year design life)
Case study - Scotland
120 plot site
46 plots on lime modified
engineered fill
Soils - soft weathered glacial till
Depths of treatment 1m to 4.7m
Platform required to achieve
bearing capacity of 100kN/m2 and
total settlement less <25mm
Case study - Scotland
Binder : Lime (CaO) @ 3%w/w
Fill compacted in 250mm lifts
Compaction specification: end
product 95% relative compaction
(4.5kg hammer)
Material testing: grading, MC,LL,PL,
organic matter, water soluble
sulphates, lab compaction tests etc
Case study - Scotland
Post compaction validation
In situ density and MC on each
layer @ 1: 250m2 with paired
sand replacement tests
600mm diameter plate bearing test
at 1 per 3 house plots to 125kN/m2
Post completion surface settlement
monitoring
The future……….
The NHBC Foundation
Established in 2006, the NHBC Foundation provides
the house building industry with research and
guidance on topical subjects to support industry
challenges leading up to the Government’s 2016 zero
carbon homes target.
NHBC Foundation Project - The
use of lime and cement stabilised
soils on residential housing
developments
Thank you
Questions
