What happened
The revised National Planning Policy Framework (NPPF) in England gives flood risk and coastal change a dedicated chapter, links sustainable drainage systems (SuDS) more clearly to the National Standards and places greater emphasis on how drainage systems will be maintained over the lifetime of a development.
Writing in Ground Engineering, Terram national key account manager Adam Brooksbank argues that the changes are a genuine improvement, but not a replacement for implementing Schedule 3 of the Flood and Water Management Act 2010.
Schedule 3 would introduce a statutory approval and adoption framework for SuDS, with clearer responsibility for their operation and long-term maintenance. Without it, a drainage strategy may look satisfactory at planning stage but still be reduced through value engineering, altered during construction or handed over without a credible maintenance arrangement.
Does this affect you?
This matters most if you undertake groundworks, drainage, external works, car parks, hard or soft landscaping, or civils on housing and commercial projects in England.
If your work is entirely indoors — such as fit-out, internal M&E or joinery — you can stop reading.
The commercial point is narrow but important: the planning drainage strategy you priced may not be the solution ultimately constructed, particularly where value engineering or construction-stage changes are introduced.
The NPPF does not automatically give you an entitlement to additional payment. That will depend on your subcontract, agreed scope, drawing hierarchy and design responsibility. However, keeping a clear record of exactly what you priced makes it much easier to demonstrate and value any subsequent change.
Subby Mate: if you are on the tools
The one thing: Before you excavate, install drainage or lay permeable surfacing, save or photograph the title block of the drawing you are working to, including its drawing number, revision and date. Email it to your contact at the main contractor and write:
Confirming that this is the current drainage drawing being used for our pricing and works. Please confirm.
Keep the drawing and the reply.
- Drainage elements may be reduced as a cost-saving measure or altered during construction. If the design changes after your price has been agreed, it may constitute a variation. If you cannot demonstrate which revision you priced, proving the change and recovering any resulting cost becomes much harder.
- Permeable surfacing — including grass-filled or gravel-filled reinforcement systems used for parking and access areas — is not the same as conventional impermeable surfacing. The required subbase, excavation, ground assessment, testing and maintenance may all differ. If the specification changes during the job, notify your contact immediately and say:
This requires a different build-up and may affect our price and programme. Please issue the change in writing so that we can assess its implications before proceeding.
- Ask in writing who will inspect, approve, adopt and maintain the completed drainage system. Depending on the project, this could involve a water company, local authority, highway authority, management company or another asset owner. If nobody can give you a clear answer, raise it before completion rather than waiting for a post-handover performance issue or remedial request.
If you are a subcontractor QS
- Add a drawing revision schedule to your quotations. List the exact drawing numbers, titles, revisions and dates included in your price. A fixed pricing baseline helps demonstrate whether a later revision changes the agreed scope.
- Price permeable and impermeable surfacing separately. State the build-up included for each system and identify the assumptions covering ground conditions, contamination risk, loading, drainage performance and testing. Avoid a single blended external-works rate that makes it difficult to value a later specification change.
- Obtain written confirmation of inspection, adoption and maintenance responsibilities. Before agreeing defects and performance obligations, establish who will inspect, approve, adopt and maintain the completed system.
- Qualify uncertain post-handover exposure. Where no adopting or maintaining body has been identified, consider stating that your price excludes third-party testing or remediation instructed after handover unless caused by a proven defect in your work. Make the qualification clear in the covering email rather than burying it in the quotation.
- Check the subcontract before calling something a variation. Confirm the agreed scope, design responsibility, document hierarchy and variation procedure. A revised drawing is useful evidence, but entitlement will still depend on the subcontract terms.
If you are a main contractor QS
- Do not approve drainage savings on cost alone. Before accepting a value-engineered drainage proposal, obtain written confirmation from the responsible designer that the revised scheme remains compliant with the approved drainage strategy, planning conditions and applicable National Standards.
- Control construction-stage changes. Make sure revised drainage details are formally issued, technically reviewed and reflected in the subcontract scope. An informal site alteration can create a gap between the approved design, the installation and the eventual handover information.
- Check the adoption and maintenance route. Review whether your external-works subcontracts include maintenance or performance obligations that do not align with the project’s intended adoption arrangements. Retaining a maintenance liability without a confirmed party to take over the asset is an exposure being stored for later.
- State the design assumptions for permeable systems. Where permeable surfacing is specified for parking, access or service areas, identify the relevant ground conditions, contamination risk, imposed loading, subbase design, testing requirements and maintenance assumptions. If those matters are left undefined, responsibility for a later performance failure will be difficult to allocate.
- Protect the handover record. Retain approved drawings, drainage calculations, inspection records, test results, photographs, as-built information and maintenance requirements. These records may be critical if the installed system is challenged after completion.
Risks and what to do about them
Drainage revised after tender but treated as unchanged
Record the drawing revision used for your quotation and obtain confirmation of the construction revision before starting. Compare later revisions against that fixed baseline and notify any change in accordance with the subcontract.
Permeable surfacing substituted for impermeable surfacing at the original rate
Price the systems as separate items, state the build-up and assumptions for each, and request a written instruction before carrying out a substituted design.
Post-handover remedial work where no adopting body was confirmed
Ask in writing who will inspect, approve, adopt and maintain the system. Where responsibility remains unclear, qualify third-party-driven testing and remediation while preserving responsibility for genuine defects in your own work.
The installed system differs from the approved drainage strategy
Do not rely on verbal site directions. Request an updated drawing or formal instruction and ensure the responsible designer confirms that the revised arrangement remains compliant.
Do this week
Ten minutes: Save the drainage or external-works drawing you are currently building to. Record its drawing number, revision and date, then email it to your main contractor contact asking them to confirm that it is current. Keep the drawing and their reply together.
A day, if you can spare it: Review your live drainage and external-works quotations. Split permeable and impermeable surfacing into separate items, state the build-up and assumptions for each, and add a drawing revision schedule to your standard quotation template.
That day’s work could prevent the next design change from being absorbed into your original price without proper assessment.
Source: Adapted from publicly available construction industry news, analysed by QS-AI.
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