www.paving.org.uk
pavingpermeable
for adoption
GUIDANCE FOR ACHIEVING
SUCCESSFUL LOCAL AUTHORITY
ADOPTION OF PERMEABLE PAVEMENTS
Uniclass L534:L217January 2010 – Edition 2
Adopting SUDSCurrent governmental planning guidancethroughout the UK clearly requires use ofSustainable Drainage Systems (SUDS) onall developments wherever possible andalso encourages planners to take acentral role in coordinating adoption. Thisrequirement is supported by BuildingRegulations and other national guidance,including the ‘Manual for Streets’ and‘Code for Sustainable Homes’.Importantly, draft legislation for Englandand Wales published during 2009 seeksto make sustainable drainage systems(SUDS) effectively mandatory on all newdevelopments.
Several local authorities have alreadytaken a lead and embraced the adoptionof SUDS, including permeable paving,successfully using existing legislation,such as Section 38 of the Highways Act,1980. Others, however, have raisedconcerns about some SUDS techniquesand resisted adoption – a situation whichgovernment is set to change.
If it takes effect as intended in 2011, theFlood and Water Management Bill willapply to surface water drainage from allnew buildings and roads in England andWales. Current arrangements for approval,construction, maintenance and adoptionof conventional piped drainage will bereplaced with similar procedures forSUDS. A new role for local (unitary andcounty) authorities as ‘SUDS ApprovingBodies’ (SABs) will be established andthey will be required to adopt all SUDSschemes except single properties.
Action is also being taken in Scotlandwhere a steering group has instigatedcomprehensive guidance on SUDS foradoption. A draft version of SUDS forRoads was launched in September 2009.In any event, there is a strong case for adifferent approach to CBPP than for otherSUDS techniques.
Unique characteristics of CBPPWhile most SUDS techniques fall outsidethe immediate highway area, CBPPsimply provides a sustainable alternativeto conventional impermeable paving anddrainage systems.
So, at adoption it will itself become thehighway and it is appropriate for it tobe treated similarly to conventionalhighways and associated drainage.While CBPP is popular as part of amanagement train comprising variousSUDS techniques it can equally be usedin isolation or to improve conventionaldrainage systems.
CBPP uses established engineeringtechnology and has predictableperformance proven over decades in the UK and abroad. For example, inGermany – where over 20,000,000m2
of permeable pavements are installedannually – it is treated as standardhighway construction. There is also awealth of experience in the UK withInterpave members developing a widerange of products over the years.
CBPP performanceConcern is sometimes expressed aboutthe potential for clogging up with CBPP.Research and experience shows that theinfiltration rate will decrease butstabilise with age, as shown above, dueto the build-up of detritus in thejointing aggregate.
The design allows for this factor andstudies have shown that the long-terminfiltration capability of permeablepavements will normally substantiallyexceed UK hydrological requirementswithout maintenance.
Maintenance costsIt is recommended sweeping isundertaken twice a year as a precautionagainst clogging, but this is no greaterthan is normally undertaken ontraditional pavements. However,experience suggests that this is rarelycarried out. Recent independent researchavailable at: www.paving.org.uk hasdemonstrated that Whole Life Costs aresimilar or lower than conventionalmaterials with piped drainage.
IntroductionThis document was originally published in December 2007 and is intended to helplocal authority planning, drainage, highways and adoption officers, as well asdevelopers and their consultants, with adoption issues. It should be read inconjunction with Interpave’s document Understanding Permeable Paving whichprovides essential information on all aspects of permeable pavements. It differentiates concrete block permeable paving (CBPP) from other SUDS techniquesand makes the case for its adoption as a matter of course.
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Service life in years© Dr. Sönke Borgwart
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I N T E RPAVE : P E RMEAB L E PAV I NG FOR ADOPT I ON
Typical reduction of surface infiltration rate over time.
More information is available in Understanding Permeable Pavingavailable on the Interpave website www.paving.org.uk
Planning aheadFull liaison and discussion between allstakeholders is essential from theearliest stage – before a planningapplication – and must include adoptionofficers. Planners should remember theirkey role as SUDS coordinators, requiredby governmental guidelines.
Layouts for statutory andother servicesThis issue is of fundamental importanceto the long-term performance of CBPP. Itis not necessary to design all surface
areas as permeable, as CBPP can copewith runoff from adjacent impermeablesurfaces, including roofs, based on arule of thumb ratio of 2:1 impermeable:permeable. With careful layout design,services and utilities can be locatedwithin conventional impermeable areas,service corridors or verges, avoiding theCBPP, negating the need to excavateand removing the risk of disturbing theCBPP to access these services.
This approach can also form a key partof the overall layout design bothvisually and technically, allowingdesigners to use their imaginations and
realise the aspirations of the ‘Manual forStreets’. For example (as shown above),an impermeable central carriagewaymight be employed to contain services,visually differentiated from CBPP parkingbays. Or impermeable service crossingscould also be used as pedestrian ways,clearly differentiated from CBPPintended for vehicles.
DesignInterpave’s comprehensive ‘PermeablePavements – Guide to the Design,Construction and Maintenance ofConcrete Block Permeable Pavements’
provides the latest methodology forCBPPs to:
• Support the traffic loads
• Manage surface water effectively (i.e. provide sufficient water storage)
This document includes advice on thelocation and depth of appropriatesoakage tests to replicate a permeablepavement, rather than a soakaway. It also deals with layouts and detailingsuitable for CBPP, and a growing libraryof standard details and other bestpractice advice can be found onwww.paving.org.uk.
Impermeable footway or service stripLocation of services
Impermeable footway or service strip
Permeable paving
Impermeable service crossing
Impermeable road
Permeable parking areas
Impermeable footway or service strip
Location of services
Steps to successfuladoptionAlthough CBPP is now a mainstream technology, it is essential to follow basicprecautions during design, construction and any reinstatement. Ideally CBPP shouldbe free of statutory services, to avoid the need to excavate for future maintenancework to these services. Taking the following precautions and making full use ofInterpave guidance will ensure that CBPPs are non-problematic, low-maintenance,long-life assets.
I N T E RPAVE : P E RMEAB L E PAV I NG FOR ADOPT I ON
Plan of a typical service crossing using impermeable pavement construction within a concrete block permeable pavement.
Cross section of a typical service crossing usingimpermeable pavement construction within a concrete blockpermeable pavement.
Plan of an alternative layout with services in an impermeable road.
Concrete block permeable pavement
Service crossover with impermeable block paving
or asphalt
Construction workPreventing and diverting impermeablecontaminants such as soil and mud fromentering the base and pavement surfaceboth during and after construction areimperative to ensure that the CBPP
remains permeable throughout itsdesign life. Simple practices such askeeping muddy construction equipmentwell away from the area, installing siltfences, staged excavation and temporarydrainage swales which divert runoff
away from the area should beconsidered. Often there is a needto use roads and hardstandingareas as temporary routes duringconstruction.Obviously, this would quickly blockthe open graded permeable sub-base with mud. There are varioussolutions available, all described inthe Interpave guide available viawww.paving.org.uk.
General maintenanceWhile maintenance requirementsare minimal, basic programmes
should be put in place – whether for thelocal authority’s own staff or outsidemanagement company – for inspectionevery six months for the first 2 years ofuse to check for: • adequate quantity of jointing material
in the joints• silting up of joints
• weed growth• discharge (for Systems B and C)• general structural integrity
Long-term management‘As constructed’ drawings should beprovided so that areas of CBPP can beidentified in future and the areadesignated a ‘Road of specialengineering importance’ to protect theCBPP from abuse during later works.
Commuted sumsSome adoption authorities apply‘Commuted Sums’ to SUDS techniquesrecognising that they fall outside thehighway area (such as swales and ponds)or require a higher level of maintenancethan normal. Neither applies to CBPP andthere is a strong case not to use anycommuted sums. By applying standardised details,specification and guidance (available fromInterpave) – just as conventional highwayconstruction – adopting authorities canhave confidence in the long-termperformance and life span of CBPP andconsider it a mainstream technology.
Geotextile150mmfilter drain
Open graded crushed rock
Subsoil
Soil profile turfed or seededwith fully biodegradable coir blanket
Rootzone soil over filter drainlined with geotextile
Topsoil
Permeable pavement
Subgrade
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I N T E RPAVE : P E RMEAB L E PAV I NG FOR ADOPT I ON
A typical Interpave standard detail – in this case a landscapedperimeter.
Before... ... After
OXFORDSHIRE
Oxfordshire CountyCouncil has beenparticularly active inencouraging the useof CBPPs, taking apositive andpragmatic approach toadoption.
BRISTOL
Retrofitted concreteblock permeablepavements at a Home Zone in Bristol,subsequentlyadopted by the localauthority.
LandscapingLandscaping should be designed so thatit does not cause soil and mulch to bewashed onto the permeable pavementand cause clogging. Detailing of thelandscape edge is especially important.
In conventional pavements rainwater isallowed to run across the surface togullies which collect and direct it intopipes which remove it as quickly aspossible, as it is undesirable to allowwater into conventional sub-basematerial. In contrast, concrete blockpermeable pavements have a dual roleand also act as the drainage system aswell as supporting traffic loads. Theyallow water to pass through the surface– between each block - and into theunderlying permeable sub-base where itis stored and released slowly, either intothe ground, to the next SUDSmanagement stage or to a drainagesystem. Although particularly popular fornew projects, CBPP can also beretrofitted to sites, for example duringrefurbishment work or as part of aplanned operation to reduce storm-water runoff and improve quality.
• CBPPs provide a structural pavementwhile allowing rainwater to infiltrate intothe pavement construction for temporarystorage.
• It is well established that CBPPs play animportant part in removing a wide rangeof pollutants from water passing throughthem.
• The treated water can then infiltrate tothe ground, be harvested for re-use orreleased to a water course, the nextSUDS management stage or otherdrainage system.
• CBPPs are suitable for a wide variety ofresidential, commercial and industrialapplications.
• They optimise land use by combiningtwo functions in one construction:structural paving combined with thestorage and attenuation of surface water.
• CBPPs can handle rainwater from thepavement itself, as well as from roofdrainage and impervious pavements.
Concrete block permeable paving is a unique sustainable drainage system withimportant attenuation and pollution source control characteristics. It provides anattractive pavement surface suitable for trafficking that also acts as a drainagesystem. More information is available in Understanding Permeable Paving availableon the Interpave website www.paving.org.uk
I N T E RPAVE : P E RMEAB L E PAV I NG FOR ADOPT I ON
Concrete blockpermeable paving
Determined by design
Upper geotextile (optional)Laying course
Jointing material
Subgrade
Permeable sub-base
80mm
50mm
Lower geotextile
System ATotal infiltration
Determined by design
Drainage pipe
Upper geotextile (optional)Laying course
Jointing material
Subgrade
Permeable sub-base
80mm
50mm
Lower geotextile
System B Partial infiltration
Drainage pipeImpermeable flexible membrane
Jointing material
Permeable sub-base
80mm
50mm
Determined by design
Upper geotextile (optional)Laying course
Subgrade
System C No infiltration
© BPCF Ltd 2007
t: 0116 232 5170 f: 0116 232 5197e: [email protected] www.britishprecast.org
t: 0116 232 5191 f: 0116 232 5197 e: [email protected] www.interlay.org.uk
www.paving.org.uk
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