POL 03 - Surface water run-off - BREEAM Knowledge Base

Adoption of road in the development - KBCN0331

Where a development includes roads, these are often adopted by a statutory authority (for example the Highways agency or the local authority in the UK). Where the authority will be taking responsibility for the roads, the following guidance should be followed to determine if the water run-off from the roads needs to be considered as part of the assessment:

If the road drainage system bypasses the new development's network to connect directly to the local drainage network, then the water running off from the roads does not need to be considered for this assessment. Evidence will need to be provided to demonstrate if this is the case.
If the road drainage system connects to the development drainage network before connecting to the local drainage network, then the water run off from the roads must be considered for the assessment.

Where the authority will NOT be taking responsibility for the roads, the BREEAM criteria should be followed for all drainage on site.

Flood Resilience - KBCN1478

In order to award two credits

Flood risk must be determined by a compliant, site-specific Flood Risk Assessment and cannot be based solely on on EA Flood Maps
The credits for flood risk are awarded based on the pre-development site

Sites which have a medium or high flood risk from one or more sources (pre-development) can only achieve one credit, subject to mitigation measures being implemented as part of the development. The criteria seek to encourage the development of sites in areas of low flood risk from all sources.

01/11/2021 Clarified: 'Sites which have a medium or high flood risk from one or more sources...'

Flood risk – Site situated across numerous flood zones - KBCN0532

Where a site is situated across more than one flood zone, the flood zone with the highest probability of flooding, i.e. the worst case scenario, must be considered for the purpose of the BREEAM assessment. An exception to this would be where the areas in the higher probability zone include only soft landscaping and it can be demonstrated that access to the building will be maintained in a flooding event. This is to ensure that the site has adequately managed the worst case scenario level of flood risk associated with the site's location.

22/07/2022 Applicability to HQM One confirmed
07/03/2018 Updated to include circumstances where an exception may apply.

Greenfield/Brownfield site – Definition - KBCN1259

For the purposes of this Issue, the following definitions apply: Greenfield site A site which has never been built on, includes minimal development or which has been substantially cleared of all buildings and associated fixed surface infrastructure* and has subsequently remained undisturbed for five years or more. * Typically, the site includes less than 5% residual development by area. This supersedes the definition of 'Greenfield' for this Issue in the technical manual. Brownfield site Any site which does not fall within the above definition of 'Greenfield site'

Minimising water course pollution – no water courses present - KBCN0550

The credit for 'minimising water course pollution' has to be assessed even in cases where no water courses are in close vicinity to the site under assessment. This is because the aim of this credit is to encourage developments to minimise water course pollution by restricting the discharge of potentially contaminated water from entering the public sewer. Minimising water course pollution does not focus on water directly entering water courses.

No discharge for up to 5mm rainfall - KBCN0599

The criterion requires no run-off to leave the developed site into the local watercourse(s) for a storm event that results in rainfall depths up to 5mm. It is not acceptable to collect the rainfall within an attenuation tank and allow the runoff to be released from the site at a restricted rate. This simply slows the rate at which it is released to the watercourse(s). Compliance should be based upon zero runoff from the first 5mm rainfall for 80% of events during summer and 50% in winter. This is in line with the recommendations within Chapter 24.8 of The SuDs Manual (C753), CIRIA 2015. The 5mm rainfall event is considered one of the most common rainfall events and, therefore, a system should be designed to prevent this run-off leaving the site thus protecting a receiving watercourse from pollution. Where ground conditions prohibit the use of SuDs techniques to manage the rainfall onsite or it is not be possible for the first 5mm of rainfall to be prevented from leaving a site completely. An appropriately qualified professional must explain comprehensively why this criterion cannot be fully met and design a system to meet the intent of this criterion as far as possible. Where this can be justified and all other relevant criteria have been achieved, the credit can still be awarded.

16.08.2024 Clarification added on calculation requirements and text from KBCN1059 now included.

Surface water run-off – no change in impermeable area - KBCN1212

CN 3.9 states: "Where the man-made impermeable area draining to the watercourse (natural or municipal) has decreased or remains unchanged post-development, the peak and volume rate of run-off requirements for the surface water run-off credits will be met by default… In this instance a flood risk assessment must be carried out and any opportunities identified to reduce surface water run-off are implemented." Where the flood resilience credits are not being targeted, a flood risk assessment is not required. Instead, a separate study identifying opportunities to reduce surface water run-off may be carried out, and the measures implemented. Where there is no change in impermeable area, opportunities should be identified to reduce run-off. It is not necessary to carry out a flood risk assessment to fulfill the intent of this criteria.

Surface water run-off not flooding property - KBCN0565

Where parts of a site may flood in the event of local drainage system failure, it is still possible to demonstrate compliance if the building itself will not be at risk of flooding.

Watercourse pollution from indoor parking - KBCN0545

If the design team can demonstrate that there will be absolutely no run-off from the indoor parking then the intent of the credit will be met. However, such proof would also have to demonstrate that no hydrocarbon spillage from vehicles found its way into the watercourse/sewer. It is likely that there would be water ingress from outside or that internal parking areas would have drains fitted and be cleaned regularly. In such conditions, the criteria are still applicable. The intent of this criteria is to ensure no hydrocarbons run off to any watercourse.

[KBCN Withdrawn] ~ Confirmation of low flood risk without an FRA - KBCN0582

The KBCN has been withdrawn and is no longer valid. This is because its content was created on the basis of a very specific case and should not be applied generally. The authority/organisation's confirmation is no more robust or detailed than reference to flood maps, which are not in themselves compliant without a FRA.

KBCN withdrawn on 31/03/17:

Where a national or local authority/organisation has confirmed, in writing, that the site has a low risk of flooding from all sources and that a Flood Risk Assessment (FRA) is not required then this is acceptable and the two credits can be awarded.  The authority/organisation's written confirmation is a sufficient indication that an appropriate level of flood risk assessment has been completed.  Please note that the use of relevant flood maps without this additional confirmation from the authority/organisation is not acceptable.

New Construction / International / 2016 / 09 - Pollution /

POL 03 - Surface water run-off