NHBC Requirements for Soil Capping Systems

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2 NHBC Requirements for Soil Capping Systems Graham Whitaker Engineering Land Quality Manager NHBC ELQF February

3 Contents Who is NHBC? NHBC Conditions Purpose of capping systems NHBC requirements Further information

4 Who is NHBC? Leading Warranty and Building Control provider Raising standards in the new house building industry Provide consumer protection for new homebuyers

5 Buildmark Warranty Contaminated Land Cover included under section 5 of warranty Valid Claims - Financial limits - If substance/s within the site curtilage result, or could reasonably be expected to result in a Statutory Notice being served. The maximum claim relating to a Home under Section 5 is the Original Purchase Price, up to a maximum of: 1 million for a newly built Home; or 500,000 for a converted Home

6 NHBC Conditions The CML initiative ( Revised Finalling Procedures ) Red and Green conditions Red conditions = no warranty = no mortgage = no sale NHBC Standards Chapters 4.1 and 9.2

7 Purpose of Simple Capping Systems Mitigate marginal contamination No hydrocarbons, volatiles etc Widely used (and accepted) Not suitable everywhere Needs design and verification

8 NHBC Requirements Check that capping is appropriate Design it Install it Verify it

9 Is Capping Appropriate? BRE 465 (esp Chapters 2 and 3 Design Limitations and Other Considerations) Vapours, shallow water table etc Marginal contamination

10 Design it Think about final site levels is there space for capping? BRE 465 design chart / spreadsheet It s not just 600mm Pick sensible contamination of cover values (are they achievable?) The shaded zone

11 Install it The easy bit (?) Do what you said you d do (or, what was agreed) But if plans change, let us (and LA) know, in advance ideally Look out for unsuitable materials, odours, colours etc would you want it in your garden? Remember, we ll be asking questions if we re not happy make sure those doing the work do it right

12 Verify it Soil quality (topsoil and subsoil) Soil thickness Chain of custody Reporting Lines of evidence

13 Verify it soil quality testing requirements (1) Post placement testing of materials gives high(est) confidence. but can present problems if fails! Manufactured soil: Often good records of chemical testing and repeatability separate verification testing may not be required Off-site soil tested at source: Separate verification testing may be required depending on frequency of testing, date of testing, protection of source etc

14 Verify it soil quality testing requirements (2) On-site soil stockpiled: Separate verification testing may be required depending on frequency of testing, date of testing, protection of source etc Remediated soil: Confirmation required that material is suitable for use (either through specific remediation verification report or through testing of soil) I.e. there s no simple answer it depends on the source and the available data

15 Verify it soil quality testing regime Not just BS3882, human health contaminants (inc organics) should be considered, with testing suite depending on source Soil testing ratio depends on number of plots to be built & certainty of supply : >30 plots c.1 plot in 4 20 to 30 plots c.1 plot in 3 5 to 20 plots c.1 plot in two <5 plots each plot (or more than one sample per plot)

16 Verify it soil thickness testing regime Same testing ratio as for soil quality: >30 plots c.1 plot in 4 20 to 30 plots c.1 plot in 3 5 to 20 plots c.1 plot in two <5 plots each plot (or more than one sample per plot)

17 Verify it chain of custody Important if materials verified off-site in advance Haulage delivery notes may be acceptable, but the more info the better (A selection would be acceptable) Can you confirm the certificate relates to the material imported to site? A visual inspection of soil on delivery essential (does soil visually compare with that described on suppliers test report?)

18 Verify it reporting (1) To include: Plot numbers Confirmation of depth Details of plots actually proven Photos of depth check holes Chemical test data Chain of custody Site plan showing sample and depth check locations Report

19 Verify it reporting (2) What causes problems Sampling ratio Wrong analysis Testing out of date?? Poor photos Exceeding agreed concentrations Wrong depths, missing membranes Getting info to us late in the day

20 Some typical verification photos

21 Further information NHBC Standards Extra 47 (in your pack or search online for NHBC Standards Extra 47 validation ) Or call us , ask for Engineering

22 Thank you Questions?

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