1 - Home - Partnership for South Hampshire
Draft PUSH Sustainable Development SPD
Resource Document
Introduction
Water
Energy/CO2
Materials and Waste
Health and Wellbeing
Green Roofs
Sustainable Management
Infrastructure and Major Developments
April 2009
Resource Document Contents
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|THI | | | |
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|VOLUME | | | |
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| |Introduction |1 |Introduction to this Guidance |
| | |1.1. |Purpose of this Resource Document |
| | |1.2 |Scope of this Resource Document |
| | |1.3. |Government Policy |
| | |1.4 |South East Plan Policies |
| | |1.5. |PUSH Planning Policy Framework |
| | |1.6. |The Council Core Strategy Policies |
| | |1.7. |How to use this Resource Document |
| | |2 |Sustainable Development: General |
| | |2.1 |National Policy Drivers |
| | |2.2 |Evidence Base in South Hampshire |
| | |2.3 |Design and Access Statements |
| | |2.4 |Code FSH and BREEAM |
| | |2.5 |Sustainability Checklist |
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|THIS |Water |3 | |
|VOLUME | | | |
| | |3.i |Introduction to Water |
| | |3.1 |Water Appliances |
| | |3.2 |Rainwater Harvesting |
| | |3.3 |Grey Water Recycling |
| | |3.4 |External Potable Water |
| | |3.5 |Reduction in Surface Water Runoff |
| | |3.6 |Flood Risk |
| | |3.7 |Adaptation to Climate Change |
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| |Energy/CO2 |4 | |
| | |4.i |Introduction to Energy/CO2 |
| | |4.1 |Natural Daylight |
| | |4.2 |Passive Solar Heat Gain |
| | |4.3 |Natural Ventilation |
| | |4.4 |Drying Space |
| | |4.5 |Energy Efficiency |
| | |4.6 |External Lighting |
| | |4.7 |Small Scale Zero/Low Carbon Technologies |
| | |4.8 |Zero Carbon Residential Developments |
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| |Materials and Waste |5 | |
| | |5.i |Introduction to materials and waste |
| | |5.1 |Construction Waste |
| | |5.2 |Construction Materials |
| | |5.3 |Waste Recycling |
| | |5.4 |Composting |
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| |Health and Wellbeing |6 | |
| | |6.i |Introduction to Health and Wellbeing |
| | |6.1 |Biodiversity |
| | |6.2 |Noise |
| | |6.3 |Private Space |
| | |6.4 |Lifetime Homes |
| | |6.5 |Pollution |
| | |6.7 |Accessibility |
| | |6.8 |Residential Density |
| | |6.9 |Security |
| |Green Roofs |7 | |
| | |7.i |Introduction to Green Roofs |
| | |7.1 |Green Roofs |
| |Sustainable Management |8 | |
| | |8.i |Introduction to Sustainable Management |
| | |8.1 |Building User Guides |
| | |8.2 |Considerate Constructors Scheme |
| | |8.3 |Construction Site Impacts |
| | | | |
| |Infrastructure and Major Developments |9 | |
| | |9.i |Introduction to Infrastructure and Major Developments |
| | |9.1 |Waste Management Infrastructure |
| | |9.2 |Green Infrastructure |
| | |9.3 |Large Scale Renewable Energy |
| | |9.4 |Major developments |
| |Appendices | | |
| | |A |Model Essential Requirements |
| | |B |Sustainability Checklist |
3. Water
3.i. Introduction to Water
This chapter looks at two aspects of water management:
the use of potable water (i.e. treated water from the tap), with the aim to reduce its use both in the home and in non-residential buildings as well as in associated outdoor spaces.
the way in which we manage rainfall in new development, identifying ways to reduce surface-water run-off in new development and reduce flood risk.
Potable Water
Water is becoming increasingly scarce as demand continues to increase dramatically. Over the last 30 years water consumption in the UK has risen by 70%. The average domestic water consumption is approximately 160 litres/person/day (150 l/p/day for new dwellings). There are many actions that can be taken to minimise water consumption and all should be considered. Sanitary use of water within a dwelling is significant and a number of steps can be taken to minimise consumption. Water-saving/efficient devices and appliances are just as economical to install into an existing building as they are at the initial construction phase.
Once all the possible water efficient appliances have been fitted, further significant efficiencies can be attained through recycling of rainwater and ‘greywater’. Sustainable Drainage Systems (SUDS) help to minimise the unnecessary loss of water to the mains drainage system and also reduce the likelihood of damaging and polluting flash floods.
Measures for rainwater harvesting, greywater drainage and SuDS are more economical to install during the construction phase than as part of a retro-fitting scheme, particularly in domestic situations.
Typical domestic water consumption (Source: Mid Kent Water)
3.1. Water Consumption
Buildings can be designed with appliances and fittings and management systems can be put in place to make the predicted water use of that building substantially lower than would otherwise be the case. Although the subsequent water consumption behaviour of the building’s users cannot be controlled the opportunities for using water much more sparingly are in place.
In residential buildings the following efficiency measures can be employed to reduce the building’s predicted water consumption
|APPLIANCES |DETAILS |
|Spray Taps |Many taps can be retro-fitted with a spray head to reduce the flow of water. Account should be taken of|
| |who would be using the tap and for what purposes. |
|Flow |Due to the water pressure being set by water companies, |
|Regulation |regulation is generally more applicable than restriction. The maintenance of a standard flow rate can |
| |be achieved by in-pipe fittings, or outlet fittings, such as specially adapted shower heads. |
|Water-efficient Toilets |Toilets can account for 25% of water-use in a typical |
| |household. Low-flush toilets and dual-flush toilets are inexpensive ways to rein in the amount of water|
| |used. Low-flush toilets simply use less water in the cistern, whereas dual-flush toilets can vary the |
| |flush depending on the amount of waste. |
|Urinals |Depending on the potential usage of urinals, systems to restrict flushing, or even remove flushing, can|
| |be employed. |
|Showers |Generally, showers use less water than baths, however this is mainly due to personal preference when |
| |washing. Power showers are actually more likely to waste water than a bath. Fitting a flow-regulation |
| |device to the shower head can maintain both the comfort and water-saving aspects of usage. |
|Washing Appliances |Although not strictly a construction issue, many new homes are fitted with washing machines and |
| |dishwashers, the use of energy efficient appliances (usually A or B rated) can help to cut water usage.|
|Meters |Water meters do not specifically save water themselves but can cut consumption. By linking water habits|
| |to a charging structure, it is likely that householders and businesses alike will take steps to ensure |
| |that less water is wasted. |
Devices and Appliances to Save Water (Source: Maidstone Borough Council Sustainable Construction SPD Part 1- Using Water July 2006)
Code Credits
There are mandatory requirements for decreasing levels of predicted water consumption at different levels of the Code and there are a maximum of 5 potential credits in Wat 1.
|Water consumption (litres/person/day) |Credits |Mandatory Levels |
|≤ 120 |1 |Levels 1 and 2 |
|≤ 110 |2 | |
|≤ 105 |3 |Levels 3 and 4 |
|≤ 90 |4 | |
|≤ 80 |5 |Levels 5 and 6 |
(From Wat 1 (Internal Potable water Use) CSH Technical Guide)
Credits are based on the predicted average household consumption calculated using the BRE Code Water Calculator and includes any reductions of mains supply due to rainwater harvesting and/or greywater recycling systems.
BREEAM Credits
BREEAM credits for non-residential buildings are awarded in the following ways:
based on the improvement over standard specification of water fittings, calculated using the BREEAM water calculator including the reduction of supply through rainwater or grey water systems.
where evidence that a water meter with a pulsed output will be installed on the mains supply to each building.
where evidence that a leak detection system is specified or installed.
where proximity detection shut off is provided to water supply for all urinals and
where evidence that there are established and operational maintenance procedures covering all sanitary fittings.
where evidence water consumption is monitored and recorded at least once every quarter.
Where evidence is provided to demonstrate the specification of systems that collect, store, and where necessary, treat rainwater or greywater for WC and urinal flushing purposes. (Some BREEAM assessments only, e.g. BREEAM Schools)
Model Essential Requirement 3.1
* At the time that planning permission is granted
Compliance Check
Residential:
Up to 2011: Level 3 certificates at both design and post construction phases
2012-2016: Code FSH Assessor’s reports at design stage and post construction stage stating at least 4 no. Wat 1 credits achieved.
From 2016: Level 6 Code FSH certificates at both design and post construction phases
Non-residential and Multi-residential:
Up to 2011: BREEAM Assessor’s reports at design stage and post construction stage stating at least 50% of BREEAM Water credits achieved.
2012-2016: BREEAM Assessor’s reports at design stage and post construction stage stating at least 60% of BREEAM Water credits achieved.
From 2016: BREEAM Assessor’s reports at design stage and post construction stage stating at least 70% of BREEAM Water credits achieved.
Planning Implications
More efficient appliances are unlikely to have any implications for the external visual appearance of buildings.
Further Guidance and References
ENVIRONMENT AGENCY, National Water Demand Management Centre, A Study of Domestic Greywater Recycling (2000)
ENVIRONMENT AGENCY: Assessing The Cost Of Compliance With The Code For Sustainable Homes WRc Ref: UC7231.
CIRIA, Buildings that Save Water (2001)
CIRIA. C522, Sustainable Urban Drainage Systems - design manual for England and Wales, (2000)
BRE, Water Conservation: a guide for installation and maintenance of low-flush WCs (1997) Available from CRC Tel: 020 7505 6622
BRE, Water Conservation: IP 2/00, Low Flow Showers and Flow Restrictors. (1997)
Available from CRC Tel: 020 7505 6622
DEFRA Water Supply (Water Fittings) Regulations, (1999)
3.2. Rainwater Harvesting and Greywater Recycling
Rainwater Recycling
Rainwater harvesting involves the channelling of water from one or more roofs via a filter into a storage tank placed in a convenient location. Table x displays the potential for water collection, depending on the size of roof used. Consequently, the installation of a single collection system is often more suited to a larger building; with smaller buildings benefiting from a linked, communal system, such as on a housing estate.
Rainwater harvesting potentially reduces the initial consumption of 150 litres/person/day to 80 l/p/d, although this will be dependent on rainfall and roof area. The potential rainwater yield is illustrated in the table below. The mean annual rainfall in South Hampshire is approximately 800mm
Table x
|Roof Area (m2) |50 |75 |100 |125 |150 |
|Annual Rainwater Yield (litres) |24000 |36000 |48000 |60000 |72000 |
|Average Annual Consumption | |
|(litres) |55000 |
Rainwater Annual Yield (litres)( Source: The Environment Agency)
Water harvested from roofs has been shown to be suitable for use in toilets and washing machines. Additionally, it can be used for other non-potable purposes, such as general cleaning. A dual water supply ensures that when rainfall has been minimal, appliances such as washing machines (and any other use that relies principally on rainwater) can be switched to the mains supply.
The installation of a harvesting system is more cost-effective and less
energy-intensive if incorporated at the outset of construction.
The size of the storage tank is determined by considering the amount of water available for storage (a function of roof size and local average rainfall), and the amount of water likely to be used (a function of a building’s occupancy and function).
Where the installation of a rainwater system is unlikely (such as in an existing single dwelling), smaller measures can be taken usefully e.g. the use of garden water butts, which cost less and provide a quicker return on investment. All harvesting systems will require periodic maintenance to ensure their ongoing quality and effectiveness.
[pic]
Commercial systems are usually larger, more sophisticated
versions of those used in the domestic situations.
Benefits
The main advantages to installing rainwater harvesting systems are:
Up to 50% of main supply water can be substituted by stored rainwater thereby reducing overall water supply costs significantly;
Dependence on the mains water supply is reduced and in remote areas rainwater harvesting can provide an off-site water supply;
Used as part of a storm-water management scheme it reduces the amount of storm-water runoff and can control the flow-rate off site;
The sustained water savings add value to the property as well as demonstrating commitment to conserving natural resources;
Can dramatically reduce attenuation volumes for restricted run off situations.
Greywater Recycling
Greywater – the water that has already been used in hand basins, baths and showers – can be recycled to save up to 49 litres per person per day(l/p/day) representing on average 33% of household water use. After basic processing, the water can be reused around the home, including flushing toilets, watering the garden or general cleaning purposes i.e. windows, floors etc. The installation of a greywater recycling system is more cost-effective and less energy-intensive if incorporated at the outset of construction.
[pic]
[pic]
Source: Maidstone Borough Council Sustainable Construction SPD Part 1- Using Water July 2006
Case Studies
[pic] [pic] Underground storage tank
Code Credits
The Code for Sustainable Homes has no specific credits for reducing the consumption of potable water in the home by rainwater harvesting or greywater recycling but it will help to gain extra credits under Wat 1. The amount of rainwater or greywater that it is predicted can be collected and used per person is subtracted from the total potable water used per person to arrive at the final predicted potable water consumption per person in Wat 1.
Wat 2 encourages the recycling of rainwater/greywater for external use (for landscape/garden watering). See section 3.3 below.
BREEAM Credits
There are specific extra credits under some BREEAM assessments for greywater/rainwater recycling e.g. BREEAM School and BREEAM Courts (Wat 5). Other BREEAM assessments, e.g. BREEAM Office, do not have specific extra credits however all non-residential developments which reduce their total water consumption via rainwater harvesting will achieve more credits under the water consumption heading. (e.g. Wat 1 for BREEAM Office).
Model Essential Requirement 3.2
Compliance Check
Code FSH or BREEAM Assessor’s report to confirm the amount of predicted water consumption for each building or development which is reduced separately by rainwater harvesting and grey water recycling systems.
OR
(Where rainwater harvesting or grey water recycling systems absent) Receipt of a feasibility report clearly showing how either or both systems are not feasible in practical physical terms for any particular building or development.
Planning Implications
The visual impact would normally be minimal (ground level inspection covers) as the storage tanks are typically sited underground, or under the building’s roof. There may be implications for tree planting which would not be possible over or near to underground tanks.
Further Guidance and References
WATER REGULATIONS ADVISORY SCHEME. Information and Guidance Note 09-02-04. Reclaimed Water Systems. Information about Installing, Modifying or Maintaining Reclaimed Water Systems (1999)
ENVIRONMENT AGENCY, Conserving Water in Buildings 4: Rainwater re-use,
.uk
UK RAINWATER HARVESTING ASSOCIATION (UKRHA)
Figures for UK rainfall are available from the Met Office met-.uk
CIRIA Rainwater and Greywater Use in Building, Best Practice Guidance (2001).
WRAS Reclaimed water systems – information about installing, modifying or maintaining reclaimed water systems”; 9-02-04, (1999)
BSI BS1710: Specification for identification of pipelines and services, (1984)
BSI BS EN 12056-3:2000: Gravity drainage systems inside buildings. Roof drainage, layout and calculation, (2000).
Grey Water website:
Rainwater harvesting website:
3.3. External Water Consumption
Approximately 13 % of domestic water consumption is via external taps mainly for watering the garden but also for cleaning cars and outside surfaces. Many non-residential buildings also use significant quantities of water for maintaining their landscaped areas.
Rainwater could be collected to reduce the amount of mains water used for these purposes as well as reducing the amount of water being discharged into drains and watercourses, and the risk of localised flooding and the overall water bills for householders and non-residential users.
The simplest and most cost effective system for rainwater collection is the water butt. This typically intercepts water from the rainwater down pipes. More complex central collection communal systems, (using the same principles as the water butt), are available for apartment blocks.
Collection of rainwater for use in the dwelling, e.g. for WC flushing, is covered in section 3.2 above. If a rainwater harvesting system is implemented for internal water use, external taps can also be supplied.
[pic][pic]
Source: combinedharvesters.co.uk
Code Credits
Wat 2 (External Potable Water Use) awards one credit for a correctly specified system to collect rainwater for a garden, patio or communal garden space. The size requirement for the potential maximum storage of collected rainwater varies according to the size of the dwelling and the type of garden space. Detailed specifications are provided for the rainwater collector to meet the Code’s requirements for this issue.
Pools hot tubs or other large water-using features which are fed by mains water, will automatically mean a score of zero for this issue. This rule applies whether it is an internal or external pool. Where pools are present, credits can only be awarded if the features use 100%
rainwater or 100% recycled water.
BREEAM Credits
There are no specific extra credits under BREEAM assessments for rainwater recycling to supply outside taps for non-residential buildings.
Model Essential Requirement 3.3
Compliance Check
Residential:
Code FSH Assessor’s reports at design stage and post construction stage stating that the Wat 2 credit has been achieved.
Non-residential and Multi-residential:
The developer to submit details of the amount of square metres of landscaped area (private and communal gardens) associated with the development or buildings as well the provided rainwater collection storage capacity.
Planning Implications
Rainwater can be stored out of sight underground or directly under the roof. On a domestic garden scale water butts are potentially more visible if positioned on the street side of the building. The design of the water butt can vary from typically green or black plastic to a more rustic timber barrel. Large plastic butts can be unsightly and should not be visible from the public realm, especially in conservation areas.
The detailed landscape design, if confirmed by a recognised ecological consultant, could specify planting which requires little water in which case the requirement for rainwater collection could be halved.
Further Guidance and References
Water UK, .uk
UK Rainwater Harvesting Association (UKRHA),
CIBSE, Reclaimed Water (2004)
SEERA/Environment Agency, a Toolkit for Delivering Water Management and Climate Change Adaptation through the Planning System (2005)
CIRIA, Guidance on the Integration of biodiversity and water attenuation, (2005)
WATER UK .uk
UK RAINWATER HARVESTING ASSOCIATION (UKRHA)
3.4. Reduction of Surface Water Runoff
Most of our streets, pavements and hard standings in the borough/city have been built using impermeable surfaces. Consequently, existing urban drainage systems have been constructed to remove the collected rainfall from streets, pavements and hard standing areas to a discharge point as rapidly as possible. The success of the system is tempered by adverse effects, notably:
Flooding – caused by a rapid concentration of rainwater into discharge points.
Pollution – many pollutants can be picked up with the surface run off, subsequently causing ill effects at discharge points.
Ground Water – the level of ground water can be depleted as
permeability is removed and rainwater is channelled away from the point that it fell.
Principles of Sustainable Drainage
Drainage systems can be developed in line with the ideals of sustainable development, by balancing the different issues that should be influencing the design. Surface water drainage methods that take account of quantity, quality and amenity issues are collectively referred to as Sustainable Drainage Systems (SuDS). These systems are more sustainable than conventional drainage methods because they:
Manage runoff flow rates, reducing the impact of urbanisation on flooding.
Protect or enhance water quality.
Are sympathetic to the environmental setting and the needs of the local community.
Provide a habitat for wildlife in urban watercourses.
Encourage natural groundwater recharge (where appropriate).
They do this by:
Dealing with runoff close to where the rain falls.
Managing potential pollution at its source now and in the future.
Protecting water resources from point pollution (such as accidental spills) and diffuse sources.
They may also allow new development in areas where existing sewerage systems are close to full capacity, thereby enabling development within existing urban areas. (Source: CIRIA)
Sustainable Drainage Systems
The chief objective of a sustainable drainage system is to reduce the rate of (or ‘attenuate’) the flow of surface water from roofs and hard areas which would otherwise lead to problems of local flooding and pollution. There are a number of attenuation methods which meet the BRE criteria for achieving credits for surface water runoff in the Code (Sur 1) and in the BREEAM assessments (Pol 7). These are:
|Swales |Providing temporary storage and passage of water, with some filtration and infiltration potential, |
| |these shallow vegetated surface channels are very cost effective and also provide landscape features.|
| |A swale is often adjacent to roads, car parks and residential areas. Swales mimic natural drainage |
| |patterns by allowing rainwater to run in sheets through vegetation. The vegetation helps filter |
| |pollutants in the flow and swales may also permit infiltration. If available, alkaline soils and |
| |sub-soils should be used to promote the removal and retention of metals to encourage good vegetation |
| |growth. Increasing the surface area of the vegetation exposed to run-off improves the effectiveness |
| |of the system. |
|Soakaways |Local or centralised soakaways either as full systems or as ‘overflow’ or ‘holding’ systems, in areas|
| |where local geological and hydrological |
| |conditions allow them to |
| |function. Confirmation |
| |of approval from |
| |relevant statutory |
| |body needs to be |
| |provided. A modern soakaway using |
| |modular attenuation cells |
| | |
| | |
| | |
| | |
| | |
|Green Roofs |Using the appropriate plant types, these roofs can limit |
| |discharge into drains as well as provide an element of filtration. For soil based grass roofs, |
| |calculation should be made on the basis of the infiltration, moisture retention and depth of soil. |
| |For sedum roofs, infiltration data should be provided by the manufacturer/installer.(see section 7.0 |
| |(Green Roofs) |
|Permeable Paving |Porous ground cover can reduce or remove the need for drains and sewers, as well as maintaining |
| |ground water levels in areas where local geological and hydrological conditions allow this to |
| |function, e.g. block paved surface on permeable sub-base over gravel bed to store the water and allow|
| |it to seep in to the soil. For less-permeable soils the gravel layer might be deeper and the water |
| |taken to a soakaway although this is not an option in some areas. Roads, footways and carparks can be|
| |paved with either porous blocks |
| |[pic] |
| | |
| |or with blocks which allow infiltration of water through their joints. |
| |[pic] |
| | |
| |Porous asphalts and macadams are also being trialled. |
| | |
| |One major disincentive for employing permeable paving is its limited lifespan. After perhaps 10 years|
| |(depending on conditions) the paving becomes increasingly impermeable and the only solution may be to|
| |relay the surface completely. |
|Infiltration Trenches and |Similar structures to one another, the infiltration trench provides water storage and infiltration |
|Filter Drains |through a stone-filled trench. A filter drain filters water through soil into a perforated |
| |underground pipe, providing more storage and some infiltration. |
|Basin |Basins initially retain storm water, before a process of filtration and infiltration through the |
| |underlying rocks. |
|Rainwater Harvesting |Run-off from roofs is collected as a part of a rainwater harvesting system |
|Ponds and Wetlands |As part of a wider infrastructure of SUDS, ponds and wetlands can be designed specifically – by means|
| |of intended capacity and planting – to increase storage capacity and provide a high quality filtering|
| |system. |
| |[pic] |
When systems are used to collect run-off from vehicular areas or other areas which are subject to potential pollution risks, they must be covered by appropriate pollution control measures such as interceptors etc. Specialist advice should be sought from relevant statutory authorities on what is appropriate in such instances.
The effectiveness of SuDS type systems will depend on many factors,
including run-off rates, ground conditions and topography in relation to
size, type and density of the development. It is therefore important that SuDS are designed to match local geological and hydrological conditions.
There is a potential conflict between the aspirations to increase infiltration of rainwater into the ground on brownfield sites where this rainwater could leach contaminants. This could be addressed by buffering the flow of rainwater with tanks, in a similar way that storm water is dealt with from motorways or by the use of green roofs.
Case studies
|Use of Sustainable Drainage (SuDS) – Bognor Regis Sports Centre |
|A sports centre constructed in 1999, which is owned and operated by West Sussex County Council. It includes synthetic sports |
|pitches, a multi-use games area and parking for 136 cars. |
|The total size of the site is approximately 2 ha and the capital value of the scheme was £2.5 – 3M. The main SuDS used in the |
|scheme are: |
|• Porous paving has been used in the roads and areas of car parking allowing blanket |
|infiltration. |
|• An infiltration trench has been incorporated accepting the pitch drainage. |
| |
|The scheme works with the sports centre roof and paved areas draining into the porous car parking area. The drainage of both the |
|car park and sports pitches are connected to an infiltration trench that runs along the side of the road. When heavy rain is |
|experienced, excess water flows are stored in the pitch under-drains and the car park sub-base. |
|The benefits of the scheme are: |
|• Reduced flood risk. |
|• Promotion of ground water recharge. |
Code credits
There is a mandatory requirement that the development must not make the runoff situation worse than before development.
There are two possible Code credits under Sur1 (Management of Surface Water Runoff) for using SuDS and establishing management agreements for their long term maintenance.
BREEAM credits
One credit is awarded under Pol 7 in BREEAM assessments:
‘Where evidence provided demonstrates that Sustainable Urban Drainage techniques are specified to minimise the risk of localised flooding, resulting from a loss of flood storage on site through development.’
Model Essential Requirement 3.4
Compliance Check
Residential:
Code FSH Assessor’s reports at design stage and post construction stage stating that both the Sur 1 credits have been achieved.
Non-residential and Multi-residential:
BREEAM Assessor’s reports at design stage and post construction stage stating that the Pol 7 credit has been achieved.
Planning Implications
Many of the SUDS measures, such as swales, basins and balancing ponds can be incorporated into the development’s surrounding landscape. They can also benefit the biodiversity of the site by creating new habitats. They can be positive assets but only if they are properly designed as part of that landscape and are appropriate to the site context and the development.
The measures that require large areas of surface area, such as ponds and basins, reed beds and swales may not be appropriate or feasible in high density developments. Where space at ground level is limited, soakaways, permeable hard surfacing and green roofs may be more appropriate design solutions.
It is essential that SuDS are properly maintained to ensure their
successful operation. Where SuDS are proposed, legal agreements for their maintenance, or agreed acceptable alternatives, must be secured and approved by the Council.
The Government is currently consulting on proposals to make SuDS mandatory for new development and to make Local Authorities responsible for their long term maintenance.
Further Guidance and References
BRE, Digest 365:1991 and BS EN 752-4 contain guidance on calculating the peak flow rate and determining the design flooding frequency
The Met Office (incl. figures for UK rainfall), met-.uk
British Standards Online,
The Environment Agency, environment-.uk/
DEFRA, .uk
BRE, Soakaway design (Digest 365, 1991)
BRESOAK, Soakaway design software (2007)
CIRIA, Sustainable urban drainage systems – best practice manual for England, Scotland, Wales and Northern Ireland (CIRIA Publication C523) (2001)
BS EN 752-4, Drain and sewer systems outside buildings – Hydraulic design and environmental considerations (1998)
BS EN 12056-3, Gravity drainage inside buildings – Roof drainage, Layout and
Calculations (2000)
British Council of Offices and Corporation of London, Green roofs – research advice note (2003)
Mayor of London and AUU, Living roofs (2004) .uk/mayor/auu/livingroofs
Scottish Environment Protection Agency, Environment Agency, Environment and Heritage Service, Sustainable Urban Drainage Systems: an Introduction (2003)
National SUDS working group, Interim code of practice for SD Systems (2005)
CIRIA, Source control using constructed pervious surfaces – hydraulic, structural and water quality performance issues (CIRIA Publication C582) (2001)
CIRIA, Sustainable Urban Drainage Systems: design manual for England and Wales. (CIRIA Publication C522) (2000)
Environment Agency, Pollution Protection Guidelines, General Guidelines to the Prevention of Pollution (2003)
3.6. Flood Risk
Principles
Space for new development in England is limited but no one wants to live or work in a house or business that is at risk of flooding. Coastal flooding is predicted to be an increasingly serious problem with a combination of more severe weather events and rising sea levels caused by climate change. It is also predicted that peak river flows during the next 100 years will increase by 20%.
In the adopted Planning Policy Statement 25 (PPS 25) the government has provided guidance to help planners manage flood risk and direct development to locations least likely to flood The PPS is a material planning consideration that local planning authorities must take into account when considering planning applications. PPS 25 requires all local planning authorities to include a sequential test for flood risk in their development plans. This sequential test is based on the Environment Agency’s flood zone mapping, which divides all land into three zones according to the risk of flooding. A Strategic Flood Risk Assessment (SFRA) will support this test. The Government has also produced a supporting practice guide currently published as “Living Draft” to provide practical advice on a number of topics, including flood risk assessment. This is presently due as a final issue in May 2008.
Strategic Flood Risk Assessment (SFRA)
The SFRA is a tool to facilitate a strategic approach to reducing flood risk throughout the Borough/City. It will become a powerful driver for sustainable development through a sequential approach to allocation of development in decreasing order of flood risk. It identifies flood risk across a variety of sources and incorporates the predicted effects of climate change.
The Environment Agency produce flood zone maps which identify the level of risk of flooding without the presence of defences, the zones are as follows:
|Flood Zone |Risk Level |Numerical Risk |
|1 |Little or no risk of flooding |(1 in 1000 chance (0.1%) or less in any year) |
|2 |Medium risk of flooding | (1 in 1000 to 1 in 200 chance (0.1% - 0.5%) in any |
| | |year for tidal flooding) |
| | |(1 in 1000 to 1 in 100 chance (0.1% - 1%) in any |
| | |year for river flooding) |
|3 |High risk of flooding |(1 in 200 chance (0.5%) or greater in any year for |
| | |tidal flooding) |
| | |(1 in 100 chance (1%) or greater in any year for |
| | |river flooding) |
A SFRA has been produced for the PUSH sub region and provides a snapshot of flood risk issues including climate change and flood defence asset information available in 2007. The SFRA highlights the probability and hazards of flooding for areas of land throughout the Borough/city.
One of the main reasons for carrying out SFRAs is to inform the process of the sequential test on flood risk set out in PPS 25, which requires that land at lowest risk be developed first. The Exception Test is only appropriate when there are large areas in Flood Zones 2 and 3, where the Sequential Test alone cannot deliver acceptable sites. This is where some continuing development is necessary for wider sustainable development reasons, or where landscape, heritage and nature conservation designations, eg Areas of outstanding Natural Beauty (AONBs), Sites of Special Scientific Interest (SSSIs) and World Heritage Sites (WHS), prevent the availability of unconstrained sites in lower risk areas.
Any proposals for development in EA flood zones 2 and 3 and any site greater than 1hectare require a Flood Risk Assessment (FRA) This looks at the safety of a proposed development and its potential impact on surrounding areas using more detailed scenarios.
Mitigation Measures
When constructing new properties permanent flood resistant measures are always preferable to temporary measures. Notwithstanding the sequential approach to allocating development away from areas at risk of flooding, it is essential that new developments which are proposed within flood risk areas are safe and that new developments are designed and constructed such that the health and safety and welfare of people is appropriately managed. Climate change should also be taken into account by adopting a precautionary approach and ensuring development can be adapted and managed to deal with impacts from climate change.
If building in flood risk areas cannot be avoided there are practical strategies and designs which can be implemented. None of these are guaranteed to fully prevent flooding or its associated risks:
These are also important when considering how to increase the resistance and resilience of existing communities and property to the effects of flooding.
There is a key requirement that drainage is designed to retain water onsite and reduce detrimental effects of rapid surface water runoff on downstream catchments. The implementation of Sustainable Drainage Systems (SuDs) should be an important component of new development (see Issue 3.5 above (Surface water Runoff and Flooding)).
A site on the edge of Flood Zone 2
Some Practical Design Measures for Mitigation
Ground and floor levels could be raised.
Site layout is important and the incorporation of flood escape routes that are publicly accessible with clearly displayed and well-maintained signs is essential. Vehicular access during flood condition will also normally be required. Developers should ensure that appropriate evacuation and flood response procedures are in place to manage the residual risk associated with an extreme flood event.
Culverted watercourses should be restored to open channels wherever practical.
Single storey residential developments should not normally be considered in flood risk areas.
Landscaping can be used to direct or divert floodwater away (e.g. earth bunds) unless this increases flood risk elsewhere. Pumps may be required.
Boundary walls and fencing could be designed using high water resistance materials (e.g. solid gates with waterproof seals).
Resistance and resilience should be incorporated into design of buildings and the use of sacrificial materials should be considered both internally and externally.
The likely velocity of floodwater should also be assessed as this could be a danger.
Surface water and foul drainage systems, should satisfy the requirements of the 6th edition of sewers for adoption.
If there are adequate warning systems in place it may be reasonable to locate parking or other flood compatible uses at ground floor level and people intensive uses above.
The construction of new flood defences to enable development to take place in flood risk areas should be avoided as the remaining residual risk behind flood defences are high. In the instance of river flooding creation of washlands or compensatory flood storage areas should be provided where necessary.
In order to decide which resilient measure would be effective it is necessary to know the potential depth and duration of flooding that is likely to occur. Figure x summarises the overall rationale behind the design strategies.
It should be noted that these mitigation measures cannot be used to justify development in areas of high flood risk. They are to be employed when the relevant tests have been passed and the development’s location is agreed to be unavoidable in a high risk flood zone.
Code credits
There are two possible Code credits under Sur 2 (Flood risk) if the site is in zone 1. A single credit is available for a zone 2/3 development that includes certain attenuation measures.
BREEAM credits
There is the potential for three credits in Pol 5 (Minimising flood risk) depending on the level of flood risk and with the requirement for SuDS.
Model Essential Requirement
None as already a requirement under PPS25
Planning Implications
Any application for development within flood zones 2 and 3 will need to be accompanied by a Flood Risk Assessment (FRA) which will assess flood risk and its potential impact on surrounding areas using more details of the local area than those covered within the high level SFRA. There should also be a demonstration that there are no reasonable options available in a lower flood risk category. The FRA should also assess the surface water and drainage of the area. The sequential test should be applied within the development sites themselves.
Removal of permitted development rights could be used where permitted development threatens to have a direct significant and adverse effect on a flood risk area or its flood defences and their access, or the permeability and management of surface water, or flood risk to occupants.
Mitigation measures are likely to have a visual impact on the external appearance of the development and may also influence building height and internal layout.
Case Study
An example of FLOWS Demonstration site.
The Lamb Drove project was run by Cambridgeshire County Council as part of the Flows project. This is located on the southern side of Cambourne, a new settlement approximately eight miles west of Cambridge, and comprises 35 dwellings on a one hectare site. Through an integrated system of sustainable drainage features, the site brought environmental, ecological and social benefits to residents. Implementation of SuDS included permeable paving, detention basins, swales, green roof, water butts and flood proofing.
Detention basin at Lamb Drove development, Cambridgeshire (image courtesy of Royal Haskoning)(Planning Policy Statement 25: Development and Flood risk Practice guide Pg 78.)
Further Guidance and References
DTLR Preparing for Floods February 2002
odpm_breg_600451.pdf
Association of British Insurers Strategic Planning for Flood Risk.
July 2004 .uk
EBC Eastleigh Borough Councils Strategic flood Risk Assessment
Governmentguidance Improving the flood performance of new buildings. Flood resilient construction.
Planning Policy Statement 25: Development and Flood risk Practice guide:
Environment Agency advice:
3.6. Adaptation to Climate Change (Water)
Water Resources
Changing patterns of rainfall will have a significant impact on water
resources and water quality. In the summer, warmer temperatures will
mean that demand for water grows just as supply – especially in water
in rivers and underground aquifers – declines due to lower rainfall.
Urban areas have little capacity to store drinking water and are more
likely to experience shortages during droughts.
The following actions and techniques should be employed at a neighbourhood or building level to manage increased pressures on water resources:
Rainwater harvesting (See Issue 3.2).
SUDs to store and collect water (See Issue 3.4).
Grey water recycling (See Issue 3.2).
Xeriscaping, low water use planting can greatly reduce water demand. The main principles of this landscape technique are as follows:
Select plants with some drought resistance, including grass varieties.
Ensures soils well mulched.
Design the most efficient irrigation system for the planting
Maintain and manage properly to reduce future water stress
Effective storm overflow management prevents surface water contamination.
Managing point source pollution reduces water quality risks.
Water efficient appliances (See Issue 3.1).
Green Roofs (See Issue 7.1).
Flooding
Rising sea levels, increases in average winter precipitation and in
the frequency, duration and intensity of heavy downpours will increase
flood risks. Impervious surfaces in urban areas will exacerbate
the risks by preventing rainwater from percolating into the ground.
Efforts should focus on understanding and managing flood pathways
and protecting areas at risk. The following actions and techniques should be employed at a neighbourhood or building level to manage increased flood risk:
• Strategic flood risk assessment and a sequential approach to development in the floodplain (See Issue 3.5).
• Impermeable surfaces can be replaced by SUDS (See Issue 3.4).
• Smaller scale hard barriers or managed realignment schemes.
• A second layer of setback flood defence constructed behind the original barrier. This is often used with managed realignment.
• Use of green open space and green roofs to reduce runoff and ameliorate pressure on drainage systems during heavy rainfall. (See Issue 7.1).
• Widening drains to increase drainage capacity.
• Managing flood pathways and removing ‘pinchpoints’ so that heavy rainfall can drain away.
• One way valves permanently fitted in drains and sewage pipes to prevent backflow and, as a last resort, widening drains to increase capacity.
• Flood resilient measures, including raising floor levels, electrical fittings and equipment; rain proofing and overhangs to prevent infiltration of heavy rain around doors and windows; temporary
free-standing barriers which hold back floodwater from properties.
• Flood resilient materials can withstand direct contact with floodwaters for some time without significant damage. These include concrete, vinyl and ceramic tiles, pressure-treated timber,
glass block, metal doors and cabinets.
• Removable household products like flood boards, air brick covers and flood skirts which are fitted temporarily to properties to form a barrier to water. Pipes, drains and toilet bowls can be temporarily blocked using an expandable/inflatable bung to prevent backflow. In cases of severe flooding, the stress caused by water volume can damage the structure and foundations of buildings, making it more harmful to keep water out than to let it in.
Code Credits
Many of the measures outlined above will, if successfully implemented, also reward the developer with credits in a number of issues. These include: Wat 1 and Wat 2 and Sur 1 and Sur 2.
BREEAM Credits
Many of the measures outlined above will, if successfully implemented, also reward the developer with credits in a number of issues. These include: Wat 1 & Wat 5 and Pol 5 & Pol 6.
Case Studies
Model Essential Requirement
Compliance Check
The proposed landscape must meet with the approval of the Council’s landscape architect for resilience to expected climate change.
Planning Implications
Well designed adaptation can have additional benefits for water quality and enhance public spaces. Where green space, either at ground or roof level has an additional water management function, this can help provide greater justification for such areas. Measures to ‘floodproof’ buildings will need careful design scrutiny to ensure that they do not create unattractive ground floor level environments.
Further Guidance and References
DEFRA, Climate Change impacts and adaptation: Cross-Regional Research Programme,
.uk/environment/climatechange/uk/adapt/crossreg.htm
GLOSSARY
‘Residential’ refers to all new houses and flats but not to extensions and conversions.
‘Multi-residential’ refers to institutional accommodation such as student halls of residence or sheltered housing for the elderly
‘Non-residential’ refers to all other building uses such as offices, retail buildings, schools, industrial buildings etc.
-----------------------
Typical commercial system
Typical domestic system
Showers and Baths 24%
WC Flushing 25%
Internal Tap 25%
External Tap 13%
Washing machines 9%
Dishwashers 2%
Unknown 1%
Rainwater collected from roof and filtered (1)
Calmed inlet (2) prevents disturbance of the float switch and sediments.
Submersible pump (3) delivers water via a floating suction filter (4) to WC, washing machine and garden tap.
Combined pressure switch/flow controller (5) turns pump on and off when required and provides dry running protection.
Float switch (7) controls solenoid valve (6) to provide mains water top-up via funnel (8).
Pressure hose (9) and cables are ducted through to the house through a 110mm drainage pipe (10).
Overflow trap (11) prevents foul odours from drains.
The Kingspan “Lighthouse” at the Building Research Establishment (BRE) site at Garston is a prototype house, the first to receive BRE Code for Sustainable Homes Level 6 certification in June 2007. Rainwater collects from the roof into a gutter which drains via a chain into the underground tank. The rainwater collected is used to supply the washing machine.
The Lighthouse uses greywater to flush the toilets.
Water butts
The Council requires all residential buildings to achieve the credit awarded for Wat 2 in the Code for Sustainable Homes.
The Council requires all non-residential and multi-residential development (above 500 sqm of floorspace) with associated landscape areas to design and implement a rainwater collection system with storage of at least 1 litre/sqm of landscape area.
The Lighthouse
Source: rainharvesting.co.uk
Source: TCPA 2007
Example of property boundary wall and lower sealed gate (courtesy of Severn Trent water) (DCLG).)
A swale as part of SUDS in a new housing development (courtesy of HR Wallingford) Ltd.)(DCLG)
Design Water Depth*
Approach
Mitigation Measures
Design Water Depth
above 0.6m
Design Water Depth
from 0.3 to 0.6m
Design Water Depth
up to 0.3m
Allow water through
property to avoid risk of structural damage.
Attempt to keep water out for low depths of flooding ‘Water Entry Strategy’ ***
Attempt to keep water out, in full or in part, depending on structural assessment.
If structural concerns exist follow approach above ***
Attempt to keep water out ‘Water Exclusion Strategy’
Remove building/development
from flood hazard
• Materials with low permeability up to
0.3m
• Accept water passage through building at higher water depths
• Design to drain water away after flooding
• Access to all spaces to permit drying and cleaning
Materials with low permeability to at least 0.3m
• Flood resilient materials and designs
• Access to all spaces to permit drying and cleaning
• Materials and constructions with low permeability
• Land raising, landscaping,
raised thresholds
Notes:
* Design water depth should be based on assessment of all flood types that can impact on the building
** Resistance/resilience measures can be used in conjunction with Avoidance measures to minimise overall flood risk
*** In all cases the ‘ water exclusion strategy’ can be followed for flood water depths up to 0.3m
Avoidance
Resistance/resilience**
Rationale for flood resilient and/or resistant design strategies
The Council requires all residential development to achieve at least:
Level 3 of the Code
(mandatory 3 No. Wat 1 Code credits required, ≤ 105 l/p/day)
4 No. Wat 1 Code credits ,≤ 90 l/p/day, from 2012*
Level 6 of the Code
(mandatory 5 No. Wat 1 Code credits required, ≤ 80 l/p/day) from 2016*
The Council requires all non-residential and multi-residential development above 500 sqm of floorspace to achieve at least:
50% of the available BREEAM Water credits until 2011*
60% of the available BREEAM Water credits from 2012*
70% of the available BREEAM Water credits from 2016*
The Council requires all residential development (of 10 dwellings and above) and all non-residential and multi-residential development (over 500 sqm of floorspace) at the detailed planning application stage to either:
Submit details of the rainwater harvesting and/or grey water recycling systems supplying all WC flushing and other appropriate uses for that development
Or:
Submit a feasibility study for rain water harvesting and/or grey water recycling systems for that development and implement its recommendations.
Greywater Recycling
Potential water savings with greywater recycling
Sustainability Checklist
Q.3.4: What Sustainable Drainage Systems will be employed to attenuate storm water runoff from the development’s roof areas and areas of hard standing?
Sustainability Checklist
Q.3.1: What measures will be taken to maximise water efficiency in buildings?
Sustainability Checklist
Q.3.2: What percentage of the development’s predicted water needs will be served by rainwater harvesting and/or greywater recycling?
Sustainability Checklist
Q.3.3: How will the development’s landscape area be watered?
Sustainable Checklist
Q.3.5: Is the proposed development in accordance with PPS 25?
Sustainable Checklist
Q3.7: What measures are included in this development to adapt to conditions of increased water resource stress and greater flooding risk?
The Council will require all planting associated with all residential development and all non-residential and multi-residential development above 500 sq m to be selected for resilience to summer drought
The Council requires all residential development to achieve
both Sur1 Code For Sustainable Homes credits
and
all non-residential and multi-residential development (over 500 sq m of external floor space) to achieve:
the Pol 7 BREEAM credit
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