Drainage has always been the quiet part of a planning submission. You do the infiltration tests, size the soakaway, write the strategy, and hope the Lead Local Flood Authority agrees with your assumptions. What has been missing is a single document everyone is measuring against.
The National Planning Policy Framework published on 17 August 2026 goes some way to fixing that. Flood risk and coastal change now has its own chapter — nine coded policies, F1 to F9 — plus a dedicated Annex F, and the Framework is explicit that “the annexes included with this Framework are also national planning policy”. The policy that changes day-to-day work is F8, on sustainable drainage.
What F8 does
Two things, both practical.
It names the standard. Development proposals with drainage implications should incorporate sustainable drainage systems, and those systems should be designed in accordance with the National Standards for Sustainable Drainage Systems. That’s Defra’s guidance, published 19 June 2025 and updated 30 July 2025. Until now it sat in an awkward position — a serious technical document that nobody was formally required to follow. National planning policy now points at it by name.
It brings the Lead Local Flood Authority into the frame for major development. Major schemes are expected to take account of LLFA advice, which formalises a conversation most competent applicants were having anyway — but gives the LLFA’s position more weight when it isn’t.
There’s also a watercourse limb: development should not enclose existing watercourses without compelling reasons, and de-culverting and re-naturalising river channels is encouraged where possible.
The Framework’s climate policy reinforces all of this. Policy CC3 on adaptation asks development to:
“Incorporate sustainable drainage systems to manage surface water flow rates and reduce volumes of runoff in accordance with policy F8”
So SuDS is now cross-referenced from the climate adaptation policy as well as sitting in the flood chapter. It is harder than it used to be to treat drainage as a detail to be resolved after layout.
What the National Standards actually ask for
If you haven’t read them since they landed, this is the part worth knowing. The 2025 standards replaced the thin 2015 non-statutory technical standards with seven standards that go well beyond peak flow control:
- Runoff destinations — a drainage hierarchy. Collect for non-potable use first, then infiltrate to ground, then discharge to a surface water body, then a surface water sewer, and only last a combined sewer. Evidence is expected to justify anything lower down the list.
- Management of everyday rainfall — intercept the first 5 mm of rainfall so it doesn’t leave the site as runoff.
- Management of extreme rainfall and flooding — design requirements for infiltration features and allowable discharge rates.
- Water quality — a risk assessment tailored to the land use and pollution risk.
- Amenity — multi-functional places and landscapes.
- Biodiversity — including links to Biodiversity Net Gain and Local Nature Recovery Strategies.
- Design for construction, operation, maintenance, decommissioning and structural integrity — long-term maintenance planned in, not assumed.
Look at the first standard again. Infiltration sits second in the hierarchy, behind rainwater reuse and ahead of every piped option. On most sites that means the honest answer to “can we soak away?” needs to be established with real infiltration testing, and it needs to be established early enough to influence the layout — not after the plots are drawn and there is nowhere left to put a soakaway at the required distance from foundations.
What hasn’t changed
Worth being clear about the limits.
Schedule 3 of the Flood and Water Management Act 2010 is still not commenced in England. There is no SuDS Approving Body, no separate statutory approval, and no legal duty in the way there is in Wales. Ministers have said repeatedly that better delivery may come through planning policy, adoption and maintenance rather than commencement, and that a final decision will be made “in due course”.
The National Standards themselves remain non-statutory guidance. What F8 does is give them a route into every planning decision, because the NPPF is a material consideration of critical importance. That’s a real change in weight, not a change in legal status. The practical effect is the same either way: if your drainage strategy departs from the standards, you now need a reason you’re willing to write down.
What we’d suggest doing
Test early, and test properly.
The single most common cause of a drainage strategy unravelling is an infiltration rate assumed at layout stage and disproved at technical approval. BRE Digest 365 sets out the trial pit method — three fills, the rate taken between 75% and 25% of the effective depth — and it takes a day on site plus a return visit. Doing it before the layout is fixed is cheap. Doing it after is a redesign.
The second is soakaway sizing checked at a single storm duration. The worst case isn’t always the shortest, heaviest storm — a long, moderate storm can fill a slow-draining soakaway that a cloudburst wouldn’t. BRE 365 asks you to check a range of durations, at the design return period with a climate change uplift, and take whichever needs the most storage.
SoakMonkey runs the BRE Digest 365 soakaway method in your browser — infiltration rate from your percolation results, storage sizing tested across storm durations, and a Building Control-ready report. Sizing on screen is free; the PDF export is £25 +VAT (£30 inc VAT).
If you’ve got a planning condition asking for a SuDS strategy to the National Standards and you’re not sure your site will infiltrate, get in touch — a trial pit and an hour of sizing usually settles it.
Sources: National Planning Policy Framework, August 2026 (PDF), GOV.UK — chapter 18 (policies F1–F9), Annex F, policy CC3 · National standards for sustainable drainage systems (SuDS), Defra, GOV.UK · Sustainable Drainage Systems (SuDS), House of Commons Library briefing CBP 10483, 4 February 2026 · New planning framework puts water infrastructure at heart of future development, Water Magazine, 18 August 2026