CIRIA Launches Guide for Early SuDS Planning

Early SuDS planning is now one of the decisions that shapes whether a site gets consented, built and sold well, not a technical detail to settle once the layout is fixed. That is the argument of CIRIA’s guidance Enabling development: Getting SuDS right from the start (C823F), a free 50-page guide published in September 2025, written by a team at Arup and endorsed by CIWEM. It makes the case that sustainable drainage should inform a scheme from the earliest stages of land acquisition and site allocation, long before a planning application is drawn up.

“The earlier SuDS are considered on your site, the greater the scale of benefits that can be realised and the easier they are to integrate into your scheme.” That single line is the heart of the guide.

CIRIA has paired the guidance with a short animation aimed at anyone making early decisions on a site:

Why does early SuDS planning matter?

Early SuDS planning matters because the cheapest, highest-value drainage decisions are the ones taken before a layout is fixed. Once roads, plot positions and site levels are set, sustainable drainage has to fit around whatever space is left over, which usually means smaller, harder-working and more expensive features that deliver less. Bring drainage in at the start and it shapes the layout instead of fighting it.

Too often SuDS are treated as a planning formality, addressed only at application stage or deferred until a drainage condition is discharged. CIRIA argues that this late consideration is precisely where design quality, cost and multi-functional benefit are lost.

• Design quality: drainage squeezed into leftover corners performs worse than a scheme designed around the site’s natural flow paths.
• Cost: retrofitted tanks and pipes are more expensive to build and maintain than shallow, source-control features designed in early.
• Amenity and biodiversity: rain gardens, swales and green corridors are easily lost once the layout is finalised, leaving fenced-off basins or buried storage that add no value.
• Programme: constraints spotted late trigger redesigns, objections and delays that a due-diligence check would have caught.
• Viability: flood risk or discharge problems that surface after land is bought can leave a site harder to develop, or undeliverable.

How the guide says early SuDS adds value

C823F reframes sustainable drainage as a commercial opportunity rather than a constraint. Considered up front, the guide says, SuDS can speed up the planning approval process, optimise the developable area, improve a site’s chances of being allocated in a local plan, and lift development value and saleability. The argument is aimed squarely at the people who choose and shape sites: developers, land agents, promoters, surveyors and masterplanners.

There is a technical dividend too. Because source-control SuDS manage rainfall close to where it falls and sit at shallow depth, they can cut construction and long-term maintenance costs against traditional deep piped drainage.

Handled early, SuDS protects the programme and the sale value at the same time as it settles the drainage, rather than trading one off against another.

The four gateways of early SuDS planning

The guide organises early SuDS around a series of “gateways” in the land-development process. At each one the project team widens and the drainage question sharpens, from a first due-diligence sift at acquisition through to a masterplan that has SuDS built into its bones. The stages below summarise how a site should move through them.

At every gateway the guide encourages early dialogue with the bodies that will judge the scheme: the Lead Local Flood Authority, the Environment Agency, the Local Planning Authority and the relevant water and sewerage companies. Confirming their expectations early is what prevents a redesign when drainage and layout collide.

Following the surface water discharge hierarchy

Getting SuDS right early also means designing to the surface water discharge hierarchy from the outset, rather than defaulting to a pipe and a connection. The 2025 National Standards for SuDS set the order in which a development must try to deal with its surface water:

1. Collect for reuse — rainwater harvesting where there is genuine non-potable demand.
2. Infiltrate to ground — soakaways or infiltration features, subject to ground conditions and testing.
3. Discharge to a watercourse — at rates and volumes agreed with the risk management authority.
4. Discharge to a surface water sewer — only where capacity is confirmed.
5. Discharge to a combined sewer — the last resort, once every higher option is ruled out.

Cost alone is never a sufficient reason to skip a higher tier; the standards expect evidence that each option has been maximised before moving down. Knowing where a site is likely to sit on this ladder at the acquisition stage is exactly the kind of early insight C823F is asking for. Our fuller explainer on the SuDS hierarchy walks through each tier and a worked example.

Establishing the probable discharge route early tells you how much land your drainage will need, before that land is committed to something else.

Does early SuDS planning cost developable land?

A common objection is that designing SuDS in early eats into the developable area. The guide tackles this head-on: done early, sustainable drainage tends to protect yield rather than shrink it. It is late, retrofitted drainage, forced into whatever space survives the layout, that most often costs plots.

Early SuDS can also unlock sites that look marginal. Land dismissed as too wet, too complex or too high-risk can become viable once drainage is understood and designed for from the start, so the constraint becomes part of the offer rather than a reason to walk away.

What early SuDS planning means for your scheme

The message of C823F comes down to one thing: treat sustainable drainage as a design driver from land acquisition onwards, not a box to tick at application stage. Handled that way, it protects the developable area and the programme while producing schemes that manage water better and make better places. As advisory rather than statutory guidance its impact will depend on how consistently the industry adopts it, but the direction of travel is clear. If you are appraising a site or shaping a layout, our team can bring drainage in at the right gateway; talk to us about a surface water drainage strategy that satisfies the LLFA and works for your scheme.

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