| Number of credits available | Minimum standards |
|---|---|
| 5 | No |
To avoid, reduce and delay the discharge of rainfall to public sewers and watercourses, thereby minimising the risk and impact of localised flooding on and off-site, watercourse pollution and other environmental damage.
This issue is split into three parts;
EITHER
OR (only where criteria 9 and 10 for this credit cannot be achieved):
Note that for the 1-year peak flow rate the 1-year return period event criterion applies (as described in the peak run-off criteria above).
For 'simple buildings', the below criteria should be applied in place of the surface water run-off criteria above (please see CN2 for more information).
Either of the following criteria is met:
OR
None.
|
Ref
|
Terms |
Description |
|---|---|---|
| Shell and core | ||
|
CN1 |
Applicable assessment criteria |
Both options: All criteria relevant to the building type and function apply. Refer to Appendix D – BREEAM UK New Construction and Shell and Core Project Assessments for a more detailed description of the above shell and core assessment options. |
| Simple buildings | ||
| Applicable assessment criteria |
Flood risk (1 or 2 credits)
OR
Surface water run-off (1 or 2 credits)
OR
Minimising water course pollution (1 credit)
Exemplary level credit (1 credit)
|
|
| General | ||
|
CN3 |
Alternative standards and recommendations from an appropriate statutory body See criteria 1 and 2. |
None of the credits can be awarded where the assessed development has proceeded against the recommendation of the statutory body on the basis that the flooding implications are too great (this includes a recommendation given by the statutory body even where such a recommendation cannot or is not statutorily enforced). Where the local authority (or other statutory body) has set more rigorous criteria than those above these must be met in order to achieve the relevant credit(s). |
|
CN3.1 |
Contaminated sites See criteria 5-22 |
Drainage designs for sites must take into account legislation relating to contaminated sites, however in many circumstances even on contaminated sites there may be opportunities for the installation of some SuDS techniques. Please see the Pol 03 Surface water run-off section for more details. |
| Flood resilience | ||
|
Sources of flooding See criteria 1 and 2. |
The Flood Risk Assessment (FRA) must detail the risk of flooding from the following sources:
Please see Pol 03 Surface water run-off section which provides more detail on the above sources of flooding. The content of the FRA should be based on historic trends, but should also account for predicted changes to the climate which may impact on the flood risk to the site in future. |
|
|
CN3.3 |
Functional flood plain See criterion 3. |
The BREEAM credit for locating in a flood zone of ‘medium or high annual probability’ cannot be awarded where the building is located in the functional flood plain. This is defined in the current best practice national planning guidance for each country’. If the building assessed is or has been defined as ‘water-compatible development’, confirmation should be provided from the local planning authority that they are satisfied with the proposals. |
|
CN3.4 |
Flood defences See criteria 1, 2 and 3. |
Third party defences There are many landscape feature defences, owned by third parties, which due to their location act as a flood defence by default, e.g. motorway, railway embankments, walls etc. It can be assumed that such embankments will remain in place for the lifetime of the development, unless the assessor or project team have reason to believe otherwise. For walls, assurance must be sought that the wall is likely to remain for the design life of the building. Pre-existing flood defences In an area protected by existing flood defences (designed to withstand a certain magnitude of flooding) the appropriate number of flood risk credits can be awarded where the defences reduce the risk to ‘low’ or ‘medium’ and the following conditions are met:
A statutory body’s local/regional office may be able to provide more information on existing defences in the area in which the assessed development is located. |
| 600mm threshold See criterion 3a. |
It is accepted that, for buildings located in medium and high risk flood zones, areas of the car park and site access may be allowed to flood and therefore fall below the 600mm threshold. In such cases the credit is still achievable provided safe access to the site, and the ground floor of the building can be maintained (i.e. they are 600mm above the design flood level) to ensure the building and site do not become an ‘island’ in the event of a flood. Where the development has been permitted and the ground levels of the topography/infrastructure immediately adjacent to the site fall below the 600mm threshold, the credit can still be awarded, provided there are no other practical solutions for access to the site above this level and the assessed building, and access to it, meet the assessment criteria. As much of the external site area as possible (or as required by an appropriate statutory body) should be designed at or above the threshold. For buildings located in medium or high flood risk zones, any areas used to store sensitive, historical, hazardous, valuable and perishable materials, e.g. radioactive materials, microbiological facilities, server rooms, libraries, etc., must be located above the 600mm threshold. |
|
|
CN3.6 |
Level of detail required in the FRA for smaller sites
See criteria 1 and 2. |
For smaller sites, e.g. less than 1 ha (10,000 m²), the level of detail required in an acceptable FRA will depend on the size of the site and the arrangement of buildings on that site. For a small site with a relatively simple arrangement of buildings this might consist of a brief report. For larger sites with a higher density of buildings a more detailed assessment would be appropriate. For small simple sites (2000 m² and less), an acceptable FRA could be a brief report carried out by the contractor’s engineer confirming the risk of flooding from all sources of flooding, including information obtained from the Environment Agency, water company/sewerage undertaker, other relevant statutory authorities, site investigation and local knowledge. |
| Surface water run-off | ||
|
CN3.7 |
Sites with many buildings |
Where the assessed building is part of a larger development of buildings, there are a number of options for assessment of the surface water run-off credits:
Whichever approach is taken to demonstrate compliance, it must be consistent when completing both the rate of run-off and volume of run-off calculations. |
|
CN3.8 |
Discharge to the sea or tidal estuaries |
The peak rate of run-off and volume run-off criteria can be deemed to be met by default if the site discharges rainwater directly to a tidal estuary or the sea. The site must discharge run-off directly into the tidal estuary or the sea, if these criteria are to be awarded by default. Typically, this would mean that drainage pipes would only carry run-off from the site and that they would not need to cross privately owned land outside the boundary of the development before reaching the sea. Please see Pol 03 Surface water run-off section for a definition of tidal estuary. |
|
CN3.9 |
No change in impermeable area |
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. Flow rate calculations will not need to be provided. Instead, drawings clearly showing the impermeable areas of the site draining to the watercourse should be provided for the pre- and post development scenarios. Figures must also be given (ideally on the drawings) to show a comparison between the areas of drained impermeable surfaces pre- and post development. In this instance a flood risk assessment must be carried out and any opportunities identified to reduce surface water run-off are implemented. |
|
CN3.10 |
Limiting discharge flow rate
See criterion 12. |
For the surface water run-off credits, where the limiting discharge flow rate would require a flow rate of less than 5 l/s at a discharge point, a flow rate of up to 5 l/s may be used where required to reduce the risk of blockage. |
|
CN3.11 |
Highways and impermeable areas | Where new non-adoptable highways are built, including those for developments with a mixture of buildings, all of the new impermeable surfaces must be included in calculations to demonstrate compliance with the peak rate of run-off and volume of run-off criteria. Where buildings are built beside existing highways or where adoptable highways are built, the impermeable area of the highway does not need to be included in the calculations. |
|
CN3.12 |
Derelict sites. See criteria 5,7, 11,12 and 14. |
If the site has been derelict for over five years, the Appropriate Consultant must assess the previous drainage network and make reasonable assumptions to establish probable flow rates and volumes. To do this they should use best practice simulation modelling, to determine the 1 year and 100 year peak flow rates at the relevant discharge points. To complete the calculations, a site visit prior to development will be required unless accurate data already exists from a previous survey. The resultant professional report can then be used to determine the pre-development volumes and rates of run-off. Without this professional input, the site must be deemed greenfield pre-development, assuming Soil type 5 for the calculation of the pre development site run-off. |
|
CN3.13 |
Rainwater harvesting | BS 8515 Rainwater harvesting systems: Code of Practice, Annex A 5BS 8515:2009 Rainwater harvesting systems - Code of Practice, (Annex A1:2013) must be followed where rainwater harvesting systems are specified for storm water control. To ensure flood risk is not increased if the rainwater harvesting system is, for some reason, unavailable, the exceedance flow route capacity provided in accordance with CIRIA report C635 should ignore the beneficial effect of the rainwater harvesting system. |
| Minimising watercourse pollution | ||
|
CN3.14 |
5mm discharge for minimising watercourse pollution
See criterion 15. |
In a small number of sites it may not be possible for the first 5mm of rainfall to be prevented from leaving site completely. Where this is the case, an appropriately qualified professional must design the system to ensure that the intent of this criterion has been met as far as possible and provide justifications to explain why the criterion could not be fully achieved on the site. Where this can be justified, the awarding of the water quality credit would not be affected, provided all other relevant criteria have been achieved. |
|
CN3.15 |
5mm requirement - end-of-pipe solutions
See criterion 15. |
End-of-pipe solutions, such as ponds and basins, will only be deemed to comply with the 5mm criteria where the principal run-off control to prevent discharge from the first 5mm of a rainfall event, is achieved using source control and site control methods. |
|
CN3.16 |
5mm requirement - green roofs
See criterion 15. |
Green roofs can be deemed to comply with this requirement for the rain that falls onto their surface. However evidence is still required to demonstrate that the 5mm rainfall from all other hard surfaces on-site is being dealt with, to allow this credit to be awarded. |
|
CN3.17 |
Areas that are a source of pollution
See criteria 17, 18 and 19. |
For the purpose of assessing the watercourse pollution credit, an area that presents a risk of watercourse pollution includes vehicle manoeuvring areas, car parks, waste disposal facilities, delivery and storage facilities or plant areas. |
|
CN3.18 |
Extension or infill building on existing site | Where the assessment is of an individual building on an existing site, i.e. infill development, the watercourse pollution criteria apply to areas within the construction zone that present a risk of pollution, as well as any areas external to the construction zone that are affected by the new works, i.e. drainage onto or from the proposed development. |
|
CN3.19 |
Suitable level of treatment
See criteria 16 to 22. |
In all cases the Appropriate Consultant should use their professional judgement to determine the most appropriate strategy for minimising watercourse pollution. |
|
CN3.20 |
Roof plant
See criteria 18,19, 21 and 22. |
Roof-top plant space must be considered where there is a risk from polluting substances such as petrol or oil. Refrigerants are not assessed under the pollution aspect of this issue, as the main risk of pollution is to air and not the watercourse. |
Key publications that should be referred to for guidance on calculating the peak rate of run-off include:
The calculation of greenfield run-off rates must be in accordance with IH Report 124, Flood estimation for small catchments (Marshall and Bayliss, 1994). The pro-rata method on the size of catchment detailed in Table 4.2 in The SuDS Manual, CIRIA C697 (2007) must be followed.
The calculation of greenfield run-off rates must be in accordance with IH Report 124, Flood estimation for small catchments (Marshall and Bayliss, 1994). Flood Estimation Handbook (Centre for Ecology and Hydrology, 1999) can be used for these sites as an alternative, where there is a preference to do so, but only if the catchment is considered to be suitable for its application.
The calculation of greenfield run-off rates must be in accordance with the Flood Estimation Handbook (Centre for Ecology and Hydrology, 1999) and any subsequent updates. Where the Flood Estimation Handbook is not considered appropriate for the development, IH Report 124 can be used.
The calculation of brownfield run-off rates should be as follows:
The limiting discharge for each discharge point should be calculated as the flow rates from the pre-developed site. The calculation should include the total flow rate from the total area of the site feeding into the discharge point (this should include both BREEAM-assessed and non BREEAM-assessed parts of the development, if applicable). The discharge point is defined as the point of discharge into the watercourse/sewers (including rivers, streams, ditches, drains, cuts, culverts, dykes, sluices, public sewers and passages through which water flows, see Relevant definitions in the Pol 03 Surface water run-off section). Where this calculation results in a peak flow rate of less than 5 l/s, the limiting discharge rate may be increased up to a level of no more than 5 l/s at the point of discharge from the site to reduce the risk of blockage.
For example, if the flow rate for the 1 year and 100 year events were 4 l/s and 7 l/s respectively, then the limiting discharges would be 5 l/s and 7 l/s. Similarly, if it was calculated to be 2 l/s and 4 l/s, then a maximum of 5 l/s limiting discharge rate could be applied to both discharge points.
Sites should not be subdivided to enable higher overall limiting discharge rates to be claimed. It is, however, recognised that some sites may require more than one discharge point as a result of the local topography or existing surrounding drainage infrastructure, and in such cases, the limiting discharge flow rate may be increased to a level no more than 5 l/s at each discharge point. The assessor should seek evidence that the number of discharge points is necessary due to topography and/or infrastructure limitations. Evidence may be in the form of a topographical map and an explanation from the Appropriate Consultant as to why multiple discharge points are required, stating that it is not feasible to have fewer discharge points.
The storage of excess flows from the 100-year event does not necessarily have to be contained within the drainage system or SuDS features (the features designed solely for the purpose of drainage). Where appropriate, storage of some or all of this volume can be achieved using temporary surface flooding of areas such as a playing field. Specific consideration should be given to overland flow routing. Overland flood flows and temporary storage of flood water on the surface must not be so frequent as to unreasonably inconvenience residents and other users.
CIRIA publication C635 (2006) Designing for exceedance in urban drainage – good practice 10CIRIA publication C635 (2006) Designing for exceedance in urban drainage – good practice should be referred to for guidance.
| Criteria |
Interim design stage
|
Final post construction stage
|
|---|---|---|
| All |
One or more of the appropriate evidence types listed in The BREEAM evidential requirements section can be used to demonstrate compliance with these criteria. |
|
| 5 | Calculation results for the pre and post development peak rate of run-off | Refer to generic evidence requirement above |
| 8 | Information showing the proposed drainage solution, system failure flood flow routes, potential flood ponding levels and ground floor levels | As per interim design stage |
| 9, 10, 11, 12 | Calculation results for the pre and post development volume of run-off | Refer to generic evidence requirement above |
| 12 | Calculation results for the limiting discharge | As per interim design stage. |
| 6, 13, 21 | No 'specific' evidence applies at Design Stage | Relevant maintenance agreements for the ownership, long term operation and maintenance of all specified SuDS. |
| 23b, 24b.ii). | Calculation of the 5mm rainfall event from the relevant areas | Refer to generic evidence requirement above |
Please note this section will be revised when the National Standards for Sustainable Drainage and associated regulations come into force.
Table 63 Definition of flood zones by country
| Definition | England | Wales | Scotland |
|---|---|---|---|
| Low annual probability of flooding |
Zone 1 Less than 1 in 1000 chance of river and sea flooding (< 0.1%). |
Zone A Considered to be at little or no risk. Zone B If site levels are greater than the flood levels used to define adjacent extreme flood outline. |
Little or no risk area As defined for England. |
| Medium annual probability of flooding |
Zone 2 Between 1 in 100 and 1 in 1000 chance of river flooding (1% – 0.1%) and between a 1 in 200 and 1 in 1000 chance of sea flooding (0.5% – 0.1%). |
Zone B If site levels are not greater than the flood levels used to define adjacent extreme flood outline. Zone C Equal to or greater* than 0.1% (river, tidal or coastal flooding). * For the purposes of BREEAM assume upper probability of flooding no greater than that specified for England. |
Low to medium risk area Watercourse, tidal or coastal flooding in the range 0.1% – 0.5% (1:1000 – 1:200). |
| High annual probability of flooding |
Zone 3a High Probability 1 in 100 or greater chance of river flooding (>1%) and a 1 in 200 or greater chance of flooding from the sea (>0.5%). Zone 3b The Functional Floodplain Land where water has to flow or be stored in times of flood. |
Zone C1 and C2 * For the purposes of BREEAM assume the same lower and upper probability of flooding as that specified for England. |
Medium to high risk areas Annual probability of watercourse, tidal or coastal flooding: greater than 0.5% (1:200). |
| Please note: Northern Ireland PPS15 does not categorise flood risk zones and there are no similar publicly available flood maps covering Northern Ireland. Assessments in NI will therefore need to rely on-site-specific flood risk assessments, or other relevant data/surveys, to determine the extent of flood risk for a specific development, and use the same definitions as those outlined for England. The Northern Ireland Department of Environment or Rivers Agency may offer further advice or recommendations in this respect www.doeni.gov.uk and www.riversagencyni.gov.uk | |||
A sequence of management practices and control structures designed to drain surface water in a more sustainable fashion than some conventional techniques. Examples of SuDS devices include:
For more information refer to The SuDS Manual (CIRIA C697, 2007).
Wales and England
For assessment in Wales and England, the recommendations of the Environment Agency’s publication Pollution Prevention Pays Guidance, 2013 11Pollution Prevention Pays, Environment Agency, 2013. should be followed.
Scotland and Northern Ireland
For assessment in Scotland and Northern Ireland, the 'Pollution Prevention Pays Guidelines' from the Environment Agency reference the following documents which are relevant:
For the purpose of assessing the watercourse pollution credit, Pollution Prevention Guide 3 Use and design of oil separators in surface water drainage systems (2006) defines the type of areas on a development where separators are required.
PPG3 is produced on behalf of the Environment and Heritage Service (Northern Ireland), Scottish Environment Protection Agency and Environment Agency (England and Wales).
In some instances, where the risk of contamination is infrequent and potential spills will be small, oil interceptors may not be required if appropriately designed sustainable urban drainage systems are specified. Refer to PPG3 for additional guidance.
Examples of contamination legislation that should be considered includes: the Water Resources Act 1991, the Environmental Protection Act 1990, the Groundwater Directive (2006/118/EC) and, more recently the Groundwater (England and Wales) Regulations 2009. Where the site risk assessment confirms that infiltration SuDS techniques are not appropriate, SuDS techniques that do not allow infiltration, such as swales lined with an impermeable membrane, can be used. It may be the case that only some areas of the site are contaminated and therefore infiltration SuDS techniques can be used elsewhere on the site. There may also be a requirement to remediate the contaminated soils, creating opportunities for the use of infiltration SuDS post-remediation.
BREEAM UK New Construction non-domestic buildings technical manual 2014
Reference: SD5076 – Issue: 5.0
Date: 23/08/2016
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