1. Investigating the soil
When new roads are planned for adoption or improvements are proposed for existing public roads, it is crucial to conduct thorough investigations beneath the soil, known as a ground investigation. This ensures that the designs shall meet our detail designs.
To investigate the various layers of the soil, exploratory holes should be spaced between 50m and 100m adjacent to the line of the proposed carriageway and encounter all the subgrade types on the site.
Adequate samples of each soil type shall be collected from suitable depths and tested at their natural moisture content.
Understanding the strength of the subgrade
It is important to understand the strength of the soil layer the road is built on, known as the subgrade, to ensure the road is built to the correct depth to prevent deformation.
The California Bearing Ratio (CBR) determines the strength of the subgrade and shall be tested in a laboratory in accordance with BS 1377:1990 Part 4 Clause 7.2.4.4 Method 5.
If a Sustainable Drainage System (SuDS) is proposed alongside or beneath the new road, the CBR shall be tested in a laboratory in accordance with BS 1377:1990 Part 4 clause 7.3 with any swelling of the samples recorded and reported.
Samples for CBR testing shall be taken from the level the road is built on, known as the formation level, to 0.5m below, except where there are different soil types and the weakest soil type shall be sampled and tested.
Additional exploratory holes should be undertaken where ground conditions are variable; particularly where they are weak. In-situ and laboratory testing shall be undertaken as appropriate.
The lowest CBR test result shall determine the proposed construction thickness of the new road which may differ for each individual legal agreement.
If the soil is not tested to determine the CBR in accordance with the above, it shall be assumed, subject to an appropriate investigation for suitability, to be less than 1.5% and the new road designed accordingly.
The strength of cohesive or clayey soils could vary as they are susceptible to moisture, therefore the maximum acceptable design CBR on cohesive soils shall be 3% for low trafficked roads and 2% for high trafficked roads, as defined in the Road build tables.
The density of the soil type in its natural state, known as the field dry density, in accordance with BS 1377:1990 Part 9 clause 2.2 shall not be less than 90% of the maximum dry density of the same soil type as determined by the vibrating hammer test in BS EN 13286-4.
Surface water soakaway testing
To determine the rate at which surface water soaks away into the soil, known as infiltration, testing shall be carried out at the proposed location, depth and head of water when draining the new road. Testing shall be carried out at a minimum of two locations and should be no more than 150m apart.
Infiltration testing shall be carried out in accordance with the Bettess Report (1996) Infiltration drainage manual of good practice CIRIA R156, which is based on the design approach in BRE Digest 365 (1991).
Test pits are to be filled three times and should achieve 75% empty for each test. The lowest infiltration rate result shall be used when applying the appropriate factor of safety (as shown in Table 25.2 CIRIA SuDS Manual) for calculating the required hydraulic design of infiltration systems.
For effective infiltration, the soil shall be permeable and unsaturated.
Ground water level
To ensure the water in the ground does not overwhelm drainage systems through SuDS features, the highest recorded ground water level shall be a minimum of 1m below the underside of the proposed SuDS feature.
The highest ground water level shall be determined by recorded evidence over a six month wet winter period.
If high groundwater level is noted before or during construction, monitoring wells might be requested to provide further detail on fluctuating ground water levels.
Polluted land
If the land that the new road and footpath is to be built on was previously used as an industrial development including farming, for storing chemicals and disposing of waste, or has no known history, it is classed as Brownfield.
Brownfield land has a risk of containing chemicals within the soil which are harmful to people and the environment from rainwater absorbing the pollutants and draining into the ground.
Therefore Brownfield land shall be subject to contamination testing and an environmental risk assessment. Records should be maintained to enable the verification of the details of the works undertaken. During construction of the road and footpaths, should any contamination be encountered, it shall be investigated and reported to us.
Chemical content that is destructive to concrete shall be assessed in accordance with BRE Special Digest 1:2005 ‘Concrete in Aggressive Ground’.
Contaminated land which is to be removed and replaced with fill materials shall be designed and constructed in accordance with the Specification For Highway Works under the guidance of, and signed off by a Chartered Geotechnical Engineer or Chartered Civil Engineer with specific experience in the design and supervision of earthworks.
Where SuDS features are proposed alongside and under new roads, consideration shall be made where there is contamination and fill material to ensure an appropriate design reduces the risk to watercourses, groundwater and the new road construction.
Reporting ground investigation results
Investigation and testing results along with a summary section shall be submitted to us in the form of a Ground Investigation Report and shall include the following:
- Design of the proposed new road and footpath with associated drainage.
- Description of the land including:
- Topography of the land
- Boundaries around the land
- Access to the land
- Vegetation
- Water features
- Watercourses and ditches
- Surface and groundwater flows
- Any other important information such as structures.
- Geology of the land including the expected and known materials it contains.
- History of the land including:
- Past and present Ordnance Survey maps.
- Reference to known previous developments.
- Known flooding incidents and consequences.
- Made ground or fill material which is not naturally occurring including the material type and depth. This material shall be removed from beneath the new road.
- Investigation results including trial pits and exploratory holes and particle size distributions and PH values for the soil.
- Testing results shall include:
- Description of testing processes.
- Details of laboratory and accreditation status for each test.
- CBR test results.
- Soakaway test results.
- Classification as either Brownfield or Greenfield. A brownfield shall be supported by contamination test results, an environmental risk assessment and chemical content assessment.
2a. Catching surface water run-off
We will accept the maintenance of the top, root zone and above, of sustainable drainage systems or traditional systems that catch only public road and footpath surface water run-off.
Existing water courses and sewers
Existing water courses and sewers that are impacted by the new road shall be assessed, diverted or removed with the relevant consent from the appropriate authority.
Sustainable catchment
New roads and footpaths designed with sustainable drainage systems (SuDS) to catch and filter surface water using natural processes should be designed specifically to suit the layout of the new road and footpath.
Catchments shall be designed for a 1-in-100-year storm plus 40% for climate change and hydraulic calculations shall be submitted with the design and confirming all dimensions and soil characteristics. The known ground water level shall be a minimum of one metre below the underside of SuDS.
The following examples of sustainable catchments shall have specific requirements.
Rain gardens
Rain gardens shall be sized appropriately based on catchment area and soil infiltration rate to prevent over or under-watering of plants.
Topsoil depth shall be at least 200mm and selected based on plant species. Filter medium depth should depend on storage requirements. A geotextile layer should be installed to prevent small particles entering the wider surface water system.
A rodding eye should be installed for pipe maintenance.
The proposed plant types shall be submitted to, and approved by, the County Council.
Example rain garden drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Permeable tree pits
Permeable tree pits should be sized appropriately based on catchment area and soil infiltration rate with perforated pipes wrapped in a geotextile to collect small particles.
Only mature or semi-mature trees shall be used in permeable tree pits. The proposed tree types, age and soil type selection, shall be submitted to, and approved by, the County Council.
Soil depth and type should be determined based on tree species in accordance with BS 3882.
A rodding eye should be installed for pipe maintenance.
Modular units may be considered in areas of heavy loading to maintain root space and structural stability.
Example permeable tree pits drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Grass filter strips
Grass filter strips shall be 35mm below the road channel level to prevent buildup of silt at the road edge which would obstruct the surface water run-off. The filter strip shall provide a smooth and consistent longitudinal slope to encourage surface water flow.
Any obstructions, including still build up, to surface flow, shall be removed prior to adoption.
A newly built filter strip shall be protected from stormwater flows unless grass has been established. If there is less than 70% of growth after four weeks following seeding, grass shall be reseeded to establish more than 90% growth.
Swales
Swales should be designed to be infiltrating or surface conveyance wherever possible. The base of the swale shall be a minimum of 0.5m and shall have a maximum longitudinal fall of 1in16 (6%). The maximum depth of the swale shall be 600mm and shall have a minimum freeboard depth of 100mm.
Example underdrain swale (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example infiltration conveyance swale (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Filter drains
Filter drains shall not be constructed near to waste storage which may pollute the surface water.
A geotextile with a higher permeability than the surrounding soil shall be used on the inside of the trench to prevent sediment ingress.
Example filter drains drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Permeable paving
Permeable paving which catches surface water within the construction of the new road shall only be used on sites with a minimum 2.5% soaked CBR.
Example permeable paving drilling drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example permeable paving section drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Vehicle entrances crossing over SuDS
Vehicle entrances crossing over SuDS shall have a maximum gradient of 1 of 60 towards the centre of the SuDS catchment or a maximum gradient of 1 in 25 towards the road.
Geotextiles
All SuDS catchments shall include a fabric layer, known as a geotextile between the base of the SuDS and the subgrade. Geotextiles shall be selected based on the soil particle size confirmed in the ground investigation report. The permeability of the geotextile shall be compatible with the infiltration rate used for the design.
All geotextiles shall have a minimum CBR puncture resistance of three kilonewtons
Woven geotextiles shall have a minimum tensile strength of 30kN/m in each direction and pore sizes shall be 90% finer than 200/µm.
Nonwoven geotextiles shall have a minimum tensile strength of 15kN/m and a pore size 90% finer than 100/um.
Traditional catchment
Where sustainable catchment cannot be achieved, gullies will be accepted with a maximum catchment of 180 square metres for each gully.
Gullies
Gullies shall be made in precast concrete and include a sump below the outlet pipe to catch debris.
Road gullies shall be at least 750mm deep and 450mm in diameter with a 150mm outlet pipe, with a stoppered rodding eye and chain.
Footpath gullies shall be rectangular and made of self-glazed ware or precast concrete. The gullies shall be 250mm square and 475mm deep, and have a 150mm diameter outlet.
Gullies shall be laid on and surrounded with 150mm thick ST4 concrete with sulphate resisting cement.
Junction pipes for gullies which are not connected shall be fitted with temporary plastic seals and the position of all such junctions shall be clearly defined by marked and labelled stakes or tracing wires.
Precast concrete gullies shall be unreinforced and comply with the requirements of BS5911 4+A2:2010 and BSEN1917:2002. Salt glazed ware gullies shall comply with the requirements for round gullies as specified in BS65.
Example gully drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Gully covers
Gully covers shall be hinged, but not removable. In the road, they shall have an opening width of 450mm and in the footpath they shall have an opening of 300mm square.
Gully covers and frames shall be made of cast or ductile iron in accordance with BS EN 124:2015 and DMRB CD534, and shall have a minimum depth of 150mm.
Class D400 covers and frames shall be used in the road and shall have a minimum polished skid resistance value of 50.
Only flexible binder course and surface course materials contained within the Road build design section shall be used to re-instate following installation or adjustment.
Frames shall be set to level, bedded and haunched externally over the base and sides of the frame on an approved bedding material. Frames shall be bedded on a non-shrink proprietary bedding material and the compressive strength should be greater than 30 newtons per square millimetre and its tensile strength should be greater than five newtons per square millimetre. A 1:2 mix should achieve this.
Frames shall be entirely seated on precast concrete cover frame seating rings to regulate the distance between the top of the cover and the top rung to no greater than 675mm. A mortar fillet shall be provided where the corners to an opening in a slab are chamfered and the brickwork is not flush with the edges of the opening.
The upper surface of gully gratings shall be flat and slots in gratings or between gratings and frames shall not be orientated parallel to the direction of traffic.
Where gradients are greater than 1 in 50, storm pattern grids shall be provided.
2b. Draining surface water run-off
We will accept the maintenance of surface water sewers or sustainable drainage systems that drain only public road and footpath surface water run-off.
Existing water courses and sewers
Existing water courses and sewers that are impacted by the new road shall be assessed, diverted or removed with the relevant consent from the appropriate authority.
Sustainable drainage
New roads and footpaths designed with sustainable drainage systems (SuDS) shall drain surface water in a way that is similar to natural processes or to an appropriate outfall that should be designed specifically to suit the layout of the new road and footpath.
Drainage shall be designed for a 1-in-100-year storm plus 40% for climate change and hydraulic calculations shall be submitted with the design and confirming all dimensions and soil characteristics. The known ground water level shall be a minimum of one metre below the underside of SuDS.
Consideration shall be made with existing infrastructure such as underground services or building foundations and details submitted to, and approved by, us.
The following examples of sustainable drainage shall have specific requirements.
SuDS soakaways
SuDS soakaways shall use new material to backfill and reinstate with a greater infiltration rate than the lowest result from the soakaway testing.
SuDS underdrains
SuDS underdrains shall carry surface water to the wider drainage system with perforated pipes of a minimum 150 diameter laid at a self-cleansing gradient of a minimum two litres per second per hectare with necessary approvals obtained.
Vehicle entrances crossing over SuDS
Vehicle entrances crossing over SuDS shall have a surface water pipe of a minimum 225mm diameter installed under the vehicle crossing. This should have a minimum cover level of 600mm and a Type Z ST4 100mm concrete surround.
Traditional drainage
Where sustainable drainage cannot be achieved, surface water pipes will be accepted where only road and footpath surface water is drained.
Surface water pipes
This section relates to pipes with a diameter less than 600mm.
The minimum depth for pipes below the road shall be 600mm and pipes less than 1200mm below the road shall be protected with concrete type ST4 and reinforced 150mm above and below the pipe across the width of the pipe trench.
Example concrete pipe protection drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Pipes should be black in colour, have a smooth internal bore and laid as a single pipe within the trench.
Gully pipes should be designed to allow for easy maintenance may be a maximum 12m in length.
Vitrified clay pipes
Vitrified clay pipes and fittings shall have flexible mechanical joints. Pipes shall comply with the relevant requirements of BS EN 295 and BS 65 (surface water pipes only).
Unreinforced and reinforced concrete
Unreinforced and reinforced concrete pipes and fittings with flexible joints shall comply with the relevant provisions of BS EN 1916:2002 and BS5911-5:2004+A1:2010.
Thermoplastic structured twin wall pipes
Thermoplastic structured twin wall pipes and fittings shall comply with the relevant provisions of BS EN 13476-1, WIS 4-35-01 and BS EN 13476-2:2018 or BS EN 13476-3:2018+A1:2020. Pipes shall be BSi Kitemarked or have an equivalent third party certification.
Pipes less than 500mm in diameter shall have a minimum of eight kilonewtons per square metre.
Pipes greater than 500mm in diameter shall have a minimum of two kilonewtons per square metre.
When using pipes with flexible joints, the concrete protection shall be interrupted at each joint by a compressible filler.
The compressible filler should be made of bitumen-impregnated insulating board conforming to BS EN 120 and BS EN 317, or another equally compressible material. The thickness of the compressible filler shall be:
- 18mm for pipes less than 450mm in diameter
- 36mm for pipes from 450 to 1200mm in diameter
Compressible packing for use between pipes and precast concrete setting blocks should consist of bitumen damp-proof sheeting complying with BS 743.
Pipes and fittings should be examined for damage and the joint surfaces and components should be cleaned immediately before laying. The maximum length of pipe for laying is shall be three metres or 10 times the diameter of the pipe, whichever is the greater, unless welded joints are used.
An independent soil contamination and resistivity data shall be provided to determine the required external anti corrosion coating for the pipes and type of pipe seal.
All pipes and fittings should have gasket-type joints of spigot and socket or rebated form. Where a fitting is installed on a sewer length, it shall have the same internal bore as the sewer.
Cut ends of pipes should be formed to the tapers and chamfers suitable for the type of joint to be used. Where concrete pipes are cut, any exposed reinforcement shall be sealed with an epoxy resin mortar.
Pipes shall be laid so that each one is in contact with the bed throughout its length. Where socketed pipes are required to be laid on a granular or sand bed, or directly on a trench bottom, joint holes should be formed in the bedding material or formation to ensure that each pipe is uniformly supported.
Pipes should be laid on setting blocks only where a concrete bed or cradle is used and not for temporary support. Precast concrete setting blocks should have rectangular faces, with sufficient plan area to prevent punching of the blinding concrete or formation and an adequate seating for the pipes. The top face of each block being covered with two layers of compressible packing. Blocks shall be manufactured from ST4 concrete, and be cast in an approved mould. Blocks shall not be used until they have achieved a cube strength of 13.5 newtons per square millimetre.
The pipe should be marked by a detectable warning mesh located immediately on top of the pipe surrounding material. This should be colour coded as recommended in Volume 1 of the National Joint Utilities Group guidelines on the Positioning and Colour Coding of Underground Utilities.
Flexible couplings
Flexible couplings shall be in accordance with the provisions of WIS 4-41-01 and BS EN 295-4.
Flow Control Devices
Flow control devices shall be self-cleaning and require no power input or have any moving parts. A bypass door shall be fitted which could be operated at cover level. The minimum aperture shall be 75mm and have a design flow greater than four litres per second.
A site specific design and a manufacturer specification sheet of the flow control device clearly indicating the suitability of the flow control device for intended purpose, shall be submitted to, and approved by, us.
Flow control devices and fixings shall be constructed of grade 316S31 stainless steel in accordance with BS EN ISO 683.
Flow control devices should have a free discharge. Where it is not practicable to achieve a free discharge at all times, attenuation calculations showing both the free discharge and surcharge conditions shall be submitted to, and approved by, us.
Flow Control Chambers
Precast chambers are preferred however in-situ chambers could be permitted where the design of the chamber directs the incoming flow to the flow control device intake with minimal turbulent flow. The flow control device chamber shall contain a sump to act as a catchpit.
Access openings into chambers shall be of sufficient size to allow the removal and replacement of the device.
Orifice Plates
The minimum aperture shall be 75mm and designed and installed so as to prevent detritus and silt build up.
Orifice plates shall be proprietary products made from Grade 304 stainless steel with an EPDM or equivalent seal and installed in accordance with manufactures recommendations.
Orifice plates shall not be accepted as the final outlet from any drainage system.
Throttle Pipes
The minimum pipe size acceptable is 150mm.
Throttle pipes shall not be accepted as the final outlet from any drainage system.
Ancillary Devices (Penstocks, Flap valves)
Ancillary devices shall require no power input or have any mechanical parts.
Ancillary devices shall comply with the relevant European or British Standard, or have third party accreditation. All fixings shall be grade 316S31 stainless steel and in accordance with BS EN ISO 683.
Warning signs for flow control and ancillary devices
Warning signs should be located in the upstream, downstream and manholes containing ancillary devices and flow control devices. The signs should be fixed within the manhole where they could be clearly read without entering the chamber.
The signs should be designed in accordance with BS ISO 3864-1:2011 utilising sign reference BS EN ISO 7010 + A5 with supplementary text specific to the hazard.
The signs should be manufactured from materials that are not adversely affected by effluent typically found in surface water sewer systems. The signs should be clearly legible for a minimum of 10 years.
The fixings shall be Grade 316S31 stainless steel in accordance with BS970 Part 1, BS EN 10084, 10085, 10087, 10088, 10095 and 10250-4.
Surface water chambers
Manholes shall be no greater than 100 metres apart, should not be positioned within 500mm of the kerb line and should be designed and constructed in accordance with BS EN 752-3:2017.
Chambers should be built at the following positions:
- Each change of alignment or gradient
- The head of all pipe runs
- Each junction of two or more pipes (other than gully connections).
- Each change in the size of pipe
Minimum internal manhole diameters (Type A and B only) shall be in accordance with below:
- 1200mm diameter with the largest pipe less than 375mm in diameter
- 1500mm diameter with the largest pipe 375 to 700mm in diameter
- 1800mm diameter with the largest pipe 700 to 900mm in diameter
Where two or more pipes enter the manhole, the internal diameter may have to be increased to accommodate the minimum width of benching. Pipes of different diameters entering manholes should be installed with soffits at the same level.
The height of a Type A manhole (benching to slab soffit) should be in excess of 2000mm but when this is impracticable, Type B manholes could be provided subject to a minimum height of 90mm.
Precast concrete manhole units of circular cross-section for manholes shall comply with the relevant provisions of BS EN 1917 and BS 5911-3:2022.
Units which bed into bases shall be manufactured so that imposed vertical loads are transmitted directly via the full wall thickness of the unit. For joints between units and the underside of slabs, joint profiles shall be capable of withstanding applied loadings from such slabs, and spigot-ended sections shall only be used where the soffit of the slab is recessed to receive them.
The jointing material for precast units should be mortar, or a proprietary bitumen or resin mastic sealant. The jointing material should fill the joint cavity any surplus should be trimmed off and joints should be pointed on completion.
Concrete surrounds to manholes and chambers shall be C16/20 and the height of each concrete pour should not exceed 2m. Each construction joint shall break joint with the precast sections by at least 150mm.
Step rungs
Step rungs should be in accordance with BS EN 13101:2002 and provided in all manholes (except Type D) at 300mm intervals. They should be of galvanised mild steel or plastic encapsulated type.
Ladders
Ladders made of mild steel for vertical fixing should comply with the relevant provision of BS 4211, Class A and PD970. After fabrication, mild steel ladders should be hot dip galvanised in accordance with BS EN ISO 1460. Stainless steel ladders for vertical fixing should be fabricated from Grade 316S31 steel in accordance with BS EN ISO 683.
Safety chains
Safety chains shall be provided in manholes where the outgoing pipe exceeds 600mm in diameter. Safety chains should be made of mild or stainless steel.
After manufacture, mild steel safety chains should be hot dip galvanised in accordance with BS EN ISO 1460 and BS EN ISO 1461:2022. They should be eight millimetres in size in accordance with BS EN 818-1. Stainless steel safety chains should be manufactured from Grade 316S31 steel in accordance with BS 970: Part 1. When tested in accordance with BS EN 818-1:1996+A1:2008, each chain shall withstand a breaking force of 30 kilonewtons and a proof force of 15 kilonewtons.
Benching and inverts
Benching and inverts in manholes shall have a screeded, ridged finish and shall have a smooth, high strength concrete topping applied.
High strength concrete topping shall be produced, laid and finished in accordance with BS 8204-2 and the following approximate mix proportions by weight shall be used: one part cement, one part natural sand and two parts single sized coarse aggregate. Aggregates for high strength concrete topping (granolithic finish) shall be in accordance with BS EN 12620, 10mm in size and graded in accordance with Table 2 of that standard.
A rocker pipe
A rocker pipe shall be provided as close as is feasible to the outside face of any chamber into which a pipe is built. The design of the flexible joints shall be compatible with any subsequent movement.
Stub pipes
Stub pipes into manholes shall be of rigid material.
Manhole covers and frames
Manhole covers and frames shall be made in cast or ductile iron in accordance with BS EN 124:2015 and DMRB CD534, and shall have a minimum depth of 150mm.
Class D400 covers and frames shall be used in the road and shall have a minimum polished skid resistance value of 50.
Only flexible binder course and surface course materials contained within the Road build design section shall be used to re-instate following installation or adjustment.
Frames shall be set to level, bedded and haunched externally over the base and sides of the frame on an approved bedding material. Frames shall be bedded on a non-shrink proprietary bedding material and the compressive strength should be greater than 30 newtons per square millimetre and its tensile strength should be greater than five newtons per square millimetre. A 1:2 mix should achieve this.
Frames shall be entirely seated on precast concrete cover frame seating rings to regulate the distance between the top of the cover and the top rung to no greater than 675mm. A mortar fillet shall be provided where the corners to an opening in a slab are chamfered and the brickwork is not flush with the edges of the opening.
Manhole covers and frames shall be of a non-rocking design which does not rely on the use of cushion inserts.
Covers and frames shall be ergonomically designed to ensure individual lift loads in accordance with manual handling legislation and the Management of Health and Safety at Work Regulations.
Covers shall be hinged to the frame and when open they shall rest at an angle greater than 100 degrees and locked in position to prevent accidental closing. The sections of cover shall be capable of being removed from the frame to facilitate better access.
Backfill of pipe trenches
Pipe bedding and haunching shall consist of natural and/or recycled aggregate including recycled concrete aggregate complying with BS EN 13242 for coarse or fine aggregate.
Filter drains including those forming the base of swales shall be backfilled with Type B filter material which should consist of natural or recycled coarse aggregate or recycled concrete aggregate complying with BS EN 13242 and the following:
- for Type B, geometrical requirements in accordance with BS EN 13242
- a resistance to fragmentation in Category LA50 in accordance with BS EN 13242
- a water-soluble sulfate content of less than 1.9 grams of sulfate (as SO3) per litre when tested in accordance with BS EB 1711-1
- be non-plastic when tested in accordance with BS 1377:Part 2.
Maintenance on completion
All internal surfaces of pipelines, gullies, linear drainage systems and manholes shall be thoroughly cleansed to remove all detritus, without this being passed forward into existing public sewers, highway drains, or water courses.
3a. Road build design
New and improved roads shall have a 40 year design life and the build depth shall be determined by the expected traffic and the type of road, please refer to the Road build tables section.
Approved materials
All materials for roads shall be obtained from a source and supplier approved by us. See our Approved suppliers list.
Utility connections and service ducts
Utility services and service ducts shall be laid below the road, within the natural soil known as the subgrade with a minimum number of crossings.
Stabilising the subgrade
Where the strength of the subgrade is less than 1.5% CBR, different techniques can be used to stabilize the subgrade. The depth and type of technique to be used shall be submitted to, and approved by, us.
Ground stabilisation may include the addition of lime, or lime and cement to increase the strength of cohesive soils or, cement may be used to increase the strength of granular soils.
Geogrids is a geosynthetic material used for the reinforcement of unbound aggregate in low strength subgrade beneath the sub-base.
The ribs of the geogrid shall be of rectangular cross section in both the longitudinal and transverse directions with a nominal edge thickness of 1.35mm.
The Quality Control Strength of the geogrid, when tested in accordance with ISO 10319 and expressed in accordance with ISO 2602 1980 (BS 2846, Part 2, 1981), shall be 40kN/m with a peak strain of around 11% in both the longitudinal and transverse directions. In addition, typically the loads at 2% and 5% strain shall be 14kN/m and 28kN/m respectively in both the longitudinal and transverse directions.
The geogrid shall be manufactured in accordance with the Manufacturer Quality Assurance requirements BS EN ISO 9001 from polypropylene sheet, oriented in two directions so that the resulting ribs shall have a high degree of molecular orientation which continues through the area of the integral node. The geogrid shall have a minimum of 2% finely divided carbon black, as determined by BS 2782 Part 4, Method 452B: 1993, well dispersed in the polymer matrix to inhibit attack by ultraviolet light.
Geotextiles is a geosynthetic material used as a separation layer between sub-base and subgrade, and shall be laid with a minimum 500mm overlap between sheets.
The subgrade shall be smooth prior to the rolling out of the geotextile and no trafficking on the geotextile prior to placement of the sub-base or granular layers will be permitted.
Non-woven geotextiles shall have a minimum tensile strength of 15kN. This figure shall be ascertained by the Wide Width Strip Test in accordance with BS EN ISO 10319:2024. All woven geotextiles shall have a minimum tensile strength of 30kN/m in each direction. All Geotextiles shall have a minimum CBR puncture resistance of 3kN.
The geotextile shall have a permeability to water flow at right angles to its plane of not less than 10 litres per m² per second under a constant head of water of 100mm. The result shall be determined in accordance with BS EN ISO 11058:2019.
The pore O90 size shall be between 60 and 300 microns and shall be determined in accordance with BS EN ISO 12956:2020. The O90 value refers to the pore size below which lies 90% of the pore sizes in the geotextile. For woven geotextiles the pore size shall be 90% finer than 200/µm, non-woven geotextiles shall have a pore size 90% finer than 100/µm.
Geotextiles used in infiltration features shall be selected on the soil particle size confirmed in the ground investigation. This permeability of the geotextile shall be compatible with the infiltration rate used for the design.
Geotextiles shall be stored so that they will not be damaged by sunlight or ultraviolet light, or suffer mechanical damage.
Geo-composite material shall have a combination of the properties of both a geogrid and geotextile as described above.
Raising the ground
Where the subgrade beneath the road is to be raised, re-used material may be used or, new material shall be used, as a capping layer. The capping layer material shall be laid in layers not exceeding 225mm compacted thickness or appropriate to the compaction plant used, whichever is less.
Reused material shall be appropriately tested and classified as either 6F5 or sub-base material. A suitably qualified engineering consultant shall be instructed as early as possible to allow sufficient time for testing and classification and all works shall be in accordance with series SHW Series 600-Earthworks.
The following process is provided for guidance:
- Pre-testing - Samples should be taken and tested at UKAS accredited laboratory to classify the material in accordance with table 6/1 and table 6/2 in series 600 SHW. Contaminated or made ground cannot be used as an acceptable fill material.
- Earthworks method statement- should be prepared by a consultant and should detail the material to be used, the testing carried out to prove it meets a series 600 material, and how the material will be compacted on site.
- Earthworks validation report completed by consultant. This details the material used, where it has been used, thicknesses and compaction.
New material classified as 6F5 should comprise crushed rock, crushed concrete, crushed slag or combinations thereof.
Formation level
This is the finished level of the underside of the sub-base. Within 24 hours of the final preparation of the formation level it shall be covered with a minimum thickness of 150mm of compacted sub-base. Construction traffic shall not run on the prepared formation.
To prevent problems of weed growth, a suitable weed killer should be applied to the formation of a new footpath.
Frost susceptibility
Any materials used within the top 450mm of the road and footpath shall not be susceptible to frost.
If tests show the subgrade not to be susceptible to frost, a reduction in sub-base thickness may be acceptable and any proposed reduction in sub-base thickness shall be submitted to, and approved by, us.
For frost heave, materials shall be tested in accordance with BS 812: Part 124 as amended by
Clause 801 of the Specification for Highway Works Volume 1 May 2007, except that the use of the silica sand and limestone filler reference specimens is not mandatory. Materials are classified as non-frost susceptible if the mean heave is 15mm or less.
Alternative minimum depth road build
It may be acceptable to replace some of the granular foundation with bituminous materials and details shall be submitted to, and approved by, us. Consideration shall be made to the most appropriate procedures and machinery used due to the reduced strength of the granular foundation e.g. tracked rather than wheeled pavers to lay the binder course.
Should the granular foundation be replaced with bituminous material the in-situ CBR requirement on top of the sub-base is not appropriate.
Please refer to the Road build tables for minimum depth which presume the sub-grade is classified as frost susceptible and additional bituminous material has been included to provide protection.
Sub-base
Two types of sub-base shall form the granular foundation for new roads. Type 1 sub-base shall be used for non-permeable roads, and type 3 sub-base shall be used for permeable road and with voids of 15 to 20%.
Sub-base shall be made and constructed using unbound mixtures in accordance with BS EN13285:2018.
A minimum in-situ CBR value of 30% and/or a minimum stiffness of 35 MPa shall be required on all roads. CBR or stiffness values shall be determined by Plate Bearing Tests or Light Weight Drop Tests.
Binder course
This material shall be asphalt concrete of 20mm size aggregate known as AC 20 Dense Binder course in accordance with BS EN 13108-1 and the binder shall be in accordance with BS EN 12591:2009 grade 40/60.
Binder course materials shall be laid in two layers of 70mm and 60mm with a minimum thickness on 50mm and maximum thickness of 100mm.
Up to 20% of crushed recycled bituminous material may be included as an aggregate replacement in binder course mixes.
Binder course should not be left exposed for a prolonged period prior to the application of the next layer above. Exposure to weather and trafficking may result in the binder course becoming so adversely affected that replacement shall be required prior to the next layer being laid.
The binder course shall be thoroughly cleaned and a tack coat shall be applied prior to the laying of the next course.
Bond coat
Each bituminous layer shall be bonded to the bituminous layer below. Each layer should be thoroughly cleansed prior to application.
A bond coat shall provide adhesion between bituminous road layers and seal the layers to prevent water ingress ,in accordance with BS EN 13808:2013 and shall be applied hot in accordance with BS 594987:2024.
Surface course
For low trafficked roads, the material shall be asphalt concrete of 10mm aggregate size known as AC 10 Close Graded surface course in accordance with BS EN 13108-1:2016 and the binder shall be in accordance with BS EN 12591:2009 grade 70/100 or 100/150.
The aggregate shall be a coarse hardstone with a minimum polished stone value of 55, unless a higher value is stipulated by us, and shall have a maximum abrasion value of 16.
For high trafficked roads, the material shall be hot rolled asphalt known as, HRA 30/14F surf, with 20mm pre-coated chippings, in accordance with BS EN 13108-4:2016 and the binder shall be grade 40/60 (50 pen) bitumen in accordance with BS EN 13108-4:2016.
The coarse aggregate content of the mix shall be 30% with a minimum polished stone value of 45 and the pre-coated chippings shall be 14/20mm size with a minimum PSV of 60 unless a higher value is stipulated by us. The binder to coat the chippings shall be 40/60 grade in accordance with BS EN 12591:2009.
The mix shall be either LCC Special Mix or LCC Standard Mix.
Joints in bituminous material
All joints shall be made in accordance with BS 594987:2024 and shall be offset (stepped) by a minimum of 300mm from parallel joints in the layer beneath.
This shall apply to all transverse joints that have not been formed to a specific profile, joints where the asphalt abuts an existing surface and all longitudinal joints.
Joints in the binder course shall be treated in such a way as to enhance compaction and bonding.
The surface of the finished joint should not be painted/over banded due to the risk of differential skid resistance.
Before the adjacent width is laid, surface course joints shall be made by:
- Cutting back the edge to a vertical face for the full thickness of the layer
- Discarding all loosened material and painting or spraying the vertical face with a thin uniform coating of hot applied 40/60 or 70/100 paving grade bitumen, or cold applied thixotropic bituminous emulsion of similar grade or polymer modified bitumen emulsion bond coat. Surplus bitumen on the surface after the joint is made should be avoided.
Example junction with existing carriageway or permeable drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Block paving
Block pavers shall be either 60mm thick for impermeable roads or 80mm thick for permeable roads. Pavers shall be specifically designed for permeable roads.
Block pavers shall be laid in roads to a 45 degree herringbone pattern with a double stretcher to the channel and single stretcher to iron work accepting the fact that the pattern is not achievable around bends. A minimum of one third of a block cut will be required in all areas.
A transition is required when changing from block paving to traditional bituminous construction.
Example transition permeable to asphalt drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Only rectangular shaped blocks/pavers with a minimum Polished Paver Value (PPV) of 55 shall be accepted.
Pre-cast concrete paving blocks shall be chamfered and in accordance with BS EN 1338:2003 and laid in accordance with BS7533 Part 3.
Clay Pavers shall be chamfered and in accordance with BS EN 1344 and laid in accordance with BS7533 Part 3:2005+A1:2009.
Pavers for low trafficked roads shall be laid on laying course material (bedding sand) that shall be naturally occurring or crushed glass and in accordance with BS 7533-3:2005+A1:2009. Crushed rock shall be used for laying courses on high trafficked roads.
The properties of the laying course for impermeable roads shall be in accordance with Table D.3, category II of BS7533-3.
The jointing material for permeable roads shall be in accordance with the requirements of Table D.4, Table 10/1 and 10/2 of BS7533-3.
Backfilling of trenches
All trenches and other excavations beneath or within one metre of roads, footpaths and vehicle crossings, shall be refilled with sub-base.
The materials should be layered so that the compacted thickness of each layer is between 2.5 and 5 times the nominal size of the material.
Due to some trench widths alternative compaction equipment may be used.
When suitable material cannot be sourced and the width of excavation is greater than 850mm, and at an appropriate depth, approved capping material can be used.
3b. Road build tables
Soft spots and sub-grades with less than 1.5% CBR shall be laid with both an approved geotextile and geogrid or an approved geo-composite of both and the sub-base may be reduced to 300mm over an additional 410mm of 6F5 capping layer granular fill.
Low trafficked residential new roads with either a single access or accesses at both ends to the same road with no bus stops proposed shall be built to the following build depths in millimetres (mm).
Table 1 – Low trafficked asphalt residential new roads
|
Subgrade CBR value |
Sub-base without geotextile |
Sub-base with geotextile |
Binder course |
Surface course |
Total depth without geotextile |
Total depth with geotextile |
|---|---|---|---|---|---|---|
|
Below 1.5% & soft spots |
N/A |
620 |
130 |
40 |
N/A |
880 |
|
1.5 % |
N/A |
440 |
130 |
40 |
N/A |
610 |
|
2 % |
400 |
340 |
130 |
40 |
570 |
510 |
|
3 % |
310 |
300 |
130 |
40 |
480 |
470 |
|
4% or greater |
300 |
N/A |
130 |
40 |
470 |
N/A |
Table 2 – Low trafficked block paved residential new roads
|
Subgrade CBR value |
Sub-base without geotextile |
Sub-base with geotextile |
Binder course |
Laying course |
Block paver |
Total depth without geotextile |
Total depth with geotextile |
|---|---|---|---|---|---|---|---|
|
Below 1.5% & soft spots |
N/A |
620 |
90 |
30 |
60 |
N/A |
890 |
|
1.5 % |
N/A |
440 |
90 |
30 |
60 |
N/A |
620 |
|
2 % |
400 |
340 |
90 |
30 |
60 |
580 |
520 |
|
3 % |
310 |
300 |
90 |
30 |
60 |
490 |
480 |
|
4 % or greater |
270 |
N/A |
90 |
30 |
60 |
450 |
N/A |
60mm pavers may be replaced with 80mm pavers.
In specific exceptional circumstances, we might allow reducing the build depths in Tables 1 and 2 to 200mm binder course over 150mm sub-base with an approved subsoil strengthening technique on a subgrade below 2% CBR.
Table 3 – Low trafficked permeable paved residential new roads
|
Subgrade CBR value |
Sub-base Type 3 |
Binder course |
Laying course |
Block caver |
Total depth |
|---|---|---|---|---|---|
|
2.5% or greater |
300 |
130 |
50 |
80 |
490 |
Permeable paving is not suitable on a subgrade with a CBR value less than 2.5%. Additional sub-base may be proposed to meet hydraulic requirements. Binder course shall be perforated by 75mm cores at 750mm centres.
High trafficked residential new roads with access at both ends to different roads or to the same road with bus stops proposed and all industrial new roads, shall be designed with the following build depths in millimetres (mm).
Table 4 – High trafficked asphalt residential and industrial new roads
|
Subgrade CBR value |
Sub-base without geotextile |
Sub-base with geotextile |
Binder course |
Surface course |
Total depth without geotextile |
Total depth with geotextile |
|---|---|---|---|---|---|---|
|
Below 1.5% & soft spots |
N/A |
620 |
180 |
40 |
N/A |
930 |
|
1.5 % |
N/A |
440 |
130 |
40 |
N/A |
660 |
|
2 % |
400 |
340 |
180 |
40 |
620 |
560 |
|
3 % |
310 |
300 |
180 |
40 |
530 |
520 |
|
4 % |
260 |
260 |
180 |
40 |
480 |
480 |
|
5 % or greater |
230 |
N/A |
180 |
40 |
450 |
N/A |
Table 5 – High trafficked single access block paved residential and industrial new roads
|
Subgrade CBR value |
Sub-base without geotextile |
Sub-base with geotextile |
Binder course |
Laying course |
Block paver |
Total depth without geotextile |
Total depth with geotextile |
|---|---|---|---|---|---|---|---|
|
Below 1.5% & soft spots |
N/A |
620 |
120 |
30 |
80 |
N/A |
940 |
|
1.5 % |
N/A |
440 |
120 |
30 |
80 |
N/A |
670 |
|
2 % |
400 |
340 |
120 |
30 |
80 |
630 |
570 |
|
3 % |
310 |
300 |
120 |
30 |
80 |
540 |
530 |
|
4 % |
260 |
N/A |
120 |
30 |
80 |
490 |
N/A |
|
5 % or greater |
220 |
N/A |
120 |
30 |
80 |
450 |
N/A |
In specific exceptional circumstances, we might allow reducing the build depths in Tables 4 and 5 to 260mm binder course over 150mm sub-base with an approved subsoil strengthening technique on a subgrade below 2% CBR.
Public road improvements
Public road improvements shall be designed to the relevant road type build as confirmed by us during the review. The surface course for road type 0 and type 1 shall be Hot Rolled Asphalt.
|
Road type |
Sub-base |
Binder course |
Surface course |
|---|---|---|---|
|
0 |
Subject to CBR testing |
310 |
40 |
|
1 |
Subject to CBR testing |
310 |
40 |
|
2 |
Subject to CBR testing |
250 |
40 |
|
3 |
Subject to CBR testing |
200 |
40 |
|
4 |
Subject to CBR testing |
140 |
40 |
|
5 |
Subject to CBR testing |
110 |
40 |
Regardless of the CBR value, unless the subgrade has been proven to be non-frost susceptible, sub-base must be thick enough to provide 450mm of frost cover.
4. Footpath build design
New footpaths and improvements to public footpaths shall be built in accordance with DfT Inclusive Mobility and shall not have any trips or obstructions during construction when used by residents and the general public. The maximum crossfall gradient shall be 1 in 40.
For soil improvements and strengthening, raising the subgrade, formation and susceptibility to frost please refer to the Road build design section.
Approved materials
All materials for footpaths shall be obtained from a source and supplier approved by us. See Approved suppliers list.
Utility connections and service ducts
Utility services and service ducts shall be laid below the footpath, within the natural soil known as the subgrade with a minimum number of crossings. Water meters should not be installed within the footpath.
Sub-base
100mm of type 1 sub-base shall be used for footpaths and shall be made and constructed using unbound mixtures in accordance with BS EN 13285:2018.
Binder course
100mm of AC 20 Dense Binder course with a binder grade of 70/100 or 100/150 as detailed in the Road build design section shall be used where a bituminous surface course is to be laid. 60mm of the same binder course shall be used where block paving is to be laid.
Surface course
25mm of 6mm aggregate size known as AC 6 Dense surface course in accordance with BS EN 13108-1:2016 and the binder shall be in accordance with BS EN 12591:2009 grade 70/100 or 100/150.
Tack coat
The surface course shall be bonded to the bituminous layer below which should be thoroughly cleansed prior to application.
A tack coat shall provide adhesion between bituminous footpath layers and shall be either C40B4 (K1-40) or C60B3 (K1-60) of cationic bitumen emulsion in accordance with BS EN 13808:2013 and shall be applied to target rates in accordance with BS 594987:2024. The tack coat can be applied cold.
Block paving
Block pavers shall be 60mm thick as detailed in the Road build design section, rectangular in shape and shall be laid to a 45 degree herringbone pattern with a single stretcher to the outer edges on 30mm laying course.
Laying course and jointing material shall be as detailed in the Road build design section.
Footpaths adjacent natural soil
Footpaths within two metres of natural soil, such as SuDS, as described in the Catching surface water run-off section or areas of wide grass such as public open spaces, or other similar locations, may require additional stability.
Additional geosynthetic material and sub-base material shall be required to build the footpath and extend 500mm beyond either side of the footpath. These shall be:
- A geogrid over a geotextile or a composite.
- 150mm of type 1 sub-base
The binder and surface course shall be the same depths and all material shall be as detailed in the Road build design section.
Surface water soakaways within five metres of a footpath may also require additional stability due to the concentration of water within a localised area and depth.
Alternative materials
Alternative blocks, setts and slabs may be considered for individual footpaths.
Temporary footpaths
In some circumstances, temporary footpaths may be acceptable and shall be built with:
- 185mm of type 1 sub-base
- 40mm of 14mm aggregate size known as AC 14 Close Graded surface course in accordance with BS EN 13108-1:2016 and the binder shall be in accordance with BS EN 12591:2009 grade 100/150.
Tactile paving
In accordance with national guidelines tactile paving shall be installed at pedestrian crossings which shall be positioned away from vehicle crossings.
Tactile paving shall be installed using high strength blocks with dimples of size 200mm by 133mm by 60mm and concrete edging shall be laid around the outside of the blocks.
Uncontrolled pedestrian crossings shall be buff in colour and as near to the line of travel as possible along a minimum straight length of 1.2m of dropped kerbs as detailed in Kerbing and concrete section.
Service boxes (e.g. BT) should not be installed within tactile paving areas, where this is unavoidable inset covers shall be provided.
Example tactile paving drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
5. Vehicle entrances onto roads
For vehicles to access driveways from the public road there are two types of entrance, known as a vehicle crossing, depending on the type of vehicle using the driveway are either light duty or heavy duty.
For this section a driveway is either for private residential use or for users of, and deliveries to, warehouses and shops or similar, known as commercial units.
Driveways shall not drain surface water onto public roads and footpaths including sustainable drainage systems. The maximum gradient should be 1 in 25 (4%).
Light duty crossings
This type of crossing is typically used for single use driveways used by few cars and not lorries. If a footpath exists, it will continue uninterrupted in front of the driveway.
The road kerbs as detailed in the Kerbing and concrete section shall be laid 25mm above the edge of the road.
Example vehicle entrance drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
If the vehicle entrance crosses a sustainable drainage system (SuDS) and is designed to drain the surface water from the crossing into the SuDS, the road kerb shall be positioned in reverse with the square edge the same level with the edge of the road.
Example vehicle entrance with SuDS drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
A footpath edging as detailed in the Kerbing and concrete section shall be laid between the driveway and crossing, and at a level to achieve the maximum gradient of 1 in 25 (4%).
A light duty crossing shall be built, as detailed in the Road build design section with the following:
- A geosynthetic layer over a soft subgrade with less than 1.5% CBR.
- 150mm type 1 sub-base.
- 100mm of binder course (AC20 Dense Binder Course)
- 25mm of surface course (AC6 Dense Surf Surface Course) or 60mm block paver laid over 30mmof laying course.
Heavy duty crossings
This type of crossing is typically used for multiple use driveways used by many cars and lorries.
Driveways which serve a maximum of nine houses or a maximum of one commercial unit may include kerbing to the same requirement as a light duty crossing above with the crossing depth built to the Road build tables.
Driveways serving more than nine houses or more than one commercial unit shall have kerbing installed as described in the Kerbing and concrete section either side of the crossing with a sufficient radius to enable lorries to remain on the crossing whilst turning in and out of the driveway.
A channel block shall be used between the driveway and crossing as detailed in the Kerbing and concrete section.
The crossing depth shall be built to the Road build tables with a 40mm surface course made of hot rolled asphalt material as detailed in the Road build design section.
Alternatively the crossing may be built with 150mm of type 1 sub-base and 200mm of C40/50 concrete, see details in the Road build design section.
6. Kerbing and concrete
New roads and footpaths, and improvements shall be supported and restrained by kerbing and concrete.
Kerbing
Meaning road kerbs, channels and edgings which shall be in accordance with Figures NA1 and NA2 of BS EN 1340 and laid on a base of ST4 (20N/mm²) concrete.
Road kerbs shall be 125mm by 255mm half battered HB2 to create separation between roads and footpaths, and 125mm by 150mm BN2 dropped kerbs shall be used in vehicle and pedestrian crossing points.
Tapered kerbs to vehicle and pedestrian crossing points shall be 125mm by 255mm reducing to 125mm x 150mm.
Radius kerbs or radius channels shall be used in curves where the radius is 15 metres or less. For radii between 15m and 80m inclusive, straight kerbs of length 600mm shall be used, unless channels are required in which case radius kerbs and channels shall be used.
The minimum cut length of a kerb shall be 450mm and a trowel width gap shall be left at the front face of a radius.
Road kerbs shall be laid on a 150mm x 380mm concrete base.
Example standard kerb types drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Sustainable drainage system Kerbing
Sustainable drainage kerbing may utilise various inlet methods to promote water flow from new roads and footpaths into the drainage system.
The options below are provided as a typical detail for reference only. The method selected should be designed specifically to suit the layout of the new road and footpath.
Example inlet - intermittent kerb drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example inlet - quadrant drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Example inlet - offlet and reverse bullnose kerb drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Channel blocks shall be used on impermeable roads with a longitudinal gradient between 1 in 150 and 1 in 250 along the face of the road kerb. Channel blocks should have a false slope for longitudinal gradients less than 1 in 250.
Channel blocks shall be 125mm x 255mm Type CS1 and should be laid on a 150mm x 300mm concrete base.
Footpath edgings, known as external flat (EF) precast concrete edgings should be used adjacent to footpaths and vehicle entrances. They should be laid on a 75mm x 330mm concrete base.
Bedding and backing of all kerbing shall be laid and bedded on a 25mm layer of cement mortar. Concrete bedding and haunching for all kerbing shall consist of ST4 (15N/mm²) concrete of low workability.
The kerb and channel bed on new roads shall always be laid separate to the backing. This is due to the high level of kerb damage experienced on development roads and the resulting need to replace kerbs at a late stage of construction whilst causing the minimum damage to the overall construction.
Alternative kerbing methods may be used on bituminous roads where the road kerbs are to be installed later, referred to as two-stage construction, and the initial layer of binder course shall be 70mm thick with the separate road kerb base utilised as level control.
Any sacrificial blocks or road kerbs shall be removed and the correct approved road kerb installed prior to laying a further 60mm layer of binder course and/or the installation of footpaths.
Should the road binder course not provide a suitable line for the road kerb to be laid, there may be a requirement to inlay plane part of the road to ensure a perfect seal between the kerb and road binder course.
Example alternative kerbing method drawing (PDF) provided as a typical detail for reference only. Scheme-specific versions may be required.
Damaged kerbing shall be replaced prior to the application of the final road or footpath surface course. Road kerbs shall be removed from the footpath or verge side unless the road binder course is still to be laid or repaired.
Where it becomes necessary to replace kerbing following the application of final surface course to the road and footpath, a minimum two metre length of surface course, the full width of the footpath, shall be replaced. If damage is caused to the adjacent road surface course, the surface course shall be replaced for a minimum of five metres for half the width of the road.
Where more than four separate road kerbs, channels or edgings are damaged within any ten metre length, the entire ten metre length shall be replaced.
When all surfacing has finished and minor damage exists, a HAPAS approved dedicated epoxy kerb repair product, which preferably incorporates a priming system may be used except on conservation kerbing or any kerbing that have not received the final surfacing.
Concrete
Concrete shall be ready mixed concrete complying BS 8500-1:2023 and BS EN 206:2013. The maximum aggregate size shall be 20mm. Suppliers shall be members of the Quality Scheme for Ready Mixed Concrete (QSRMC) and have a quality management system in accordance with BS EN ISO 9001: 2015.
Concrete compressive strengths are defined in terms of both cylinder strength and cube strengths. The first (lower) number gives the cylinder strength requirement; the second (higher) number is the cube strength requirement.
Fresh concrete shall not be placed against concrete which has been in position for more than 30 minutes unless an approved construction joint is formed.
Standard prescribed concrete shall be in accordance with the required concrete mixes and strengths but shall not be used where:
- Sulphates or other aggressive chemicals are present in the ground water.
- Where concrete will be subjected to road de-icing salt.
In these circumstances a suitable mix, including admixtures and cement containing additives, shall be submitted to, and approved by, us.
|
Standardised prescribed concrete |
Strength Class for structural design |
Compressive cube strength at 28 days (N/mm2) |
|---|---|---|
|
ST1 |
C6/8 |
8 |
|
ST2 |
C8/10 |
10 |
|
ST3 |
C12/15 |
15 |
|
ST4 |
C16/20 |
20 |
|
ST5 |
C20/25 |
25 |
Site batched concrete may be acceptable where small quantities of concrete are required and the use of ready mix concrete would be prohibitively expensive. Site batched concrete will only be permitted in unreinforced applications and shall be in accordance with the table below.
|
Compressive Strength N/mm2 |
Coarse |
Fine |
Cement |
|---|---|---|---|
|
C12/15 |
4 |
2 ½ |
1 |
|
C16/20 |
4 |
2 |
1 |
|
C25/30 |
3 |
1 ½ |
1 |
Recycled low grade concrete mixes with 10% recycled aggregate may be used in footpath edgings and, sign and street name plate foundations. This should not be used for structural, drainage or kerbing works.
When recycled concrete aggregate is used, it shall not have more than 1% by mass of foreign materials including wood, plastic and metal nor a floating material in volume content exceeding 10cm³/kg when tested in accordance with BS EN 933-11.
Compaction shall be required for all concrete to produce a dense uniform mass. It shall be compacted with the assistance of vibrators, care being taken to avoid contact with reinforcement and inserts.
All concrete shall be compacted in its final position within 30 minutes of being discharged from the mixer unless carried in continuously operated purpose-made agitators, when the time shall not be more than 2 hours after the introduction of the cement.
Curing of all concrete shall be required for 24 hours before any fresh concrete is placed adjacent to the cured concrete.
Immediately after completion and for 7 days thereafter, concrete shall be protected against harmful effects of weather, including rain, rapid temperature changes, frost and from drying out.
7. Signing and marking roads
All traffic signs placed on public roads must be designed and displayed in accordance with the Traffic Signs Regulations and General Directions and shall be used in accordance with the Department for Transport guidelines.
For signs with supplementary plates a detailed drawing of the sign shall be submitted to, and approved by, us.
All traffic signs shall be made in accordance with BS EN 12899-1:2007 and its National Annex with a ‘CE’ mark on the rear. A sign made in micro prismatic material shall be in accordance with BS 8408:2005.
All traffic signs shall have a minimum guaranteed lifespan of seven years. For Class 1 or micro prismatic materials, the minimum guaranteed lifespan shall be 10 years.
Temporary signs for events or new housing on public roads shall be in accordance with the Department for Transport guidelines and applications shall be made to, and approved by, us. Please apply for temporary event or housing development signs.
Consideration should be given to keeping the number of temporary signs to a minimum on the public roads to avoid confusion.
Road markings
All markings on roads shall be in accordance with BS EN 1436:2018 and shall conform with the stated minimum standards of performance for a minimum period of two years from the date of application.
8. Lighting roads and footpaths
It is our policy to not light new roads and footpaths unless it is considered a requirement for safety reasons. For further information please refer to our Street Lighting Policy.
The lighting of roads and footpaths may be designed by us.
The positions of lighting columns shall be determined by the landscape design and shall be positioned a minimum of 5m away from trees within the adoptable area.
If the road or footpath layout changes, any lighting positions shall be redesigned for the new layout.
9. Culverts, bridges and walls
Where a road or footpath crosses a watercourse, to maintain the water flow, a pipe, box, known as a culvert will be required. A pipe or box less than 600mm in diameter or height shall be designed in accordance with the Draining surface water run-off section. A pipe or box 600mm or greater in diameter or height shall be known as a structure.
Bridges with a distance between supports of 600mm or greater, and walls, known as retaining walls, supporting the roads and footpaths of 600mm or greater in height shall be known as a structure.
All structures shall be designed in accordance with our guidelines for structures.
Structures supporting roads or footpaths may be designed by the County Council.
A road or footpath in a legal agreement with us shall include the supporting structures and all its parts.
Private retaining wall
A wall supporting soil and located up to 3.65m from a public road or footpath with a height greater than 1.35m must be approved by us.
Brickwork
Some headwalls and parapets may be built or clad with brick. When building brickwork above completed concrete or stonework, precautions should be in place to prevent mortar or debris from falling into the open expansion joints
Exposed joints shall be treated in the following ways:
- Pointed joints should be raked out to a depth of 14mm, pointed with mortar and finished with flush pointing.
- Un-pointed joints should be cleaned out to a depth of 14mm, filled with mortar and finished flush along with the following:
- No overhand work is allowed.
- Putlog holes must be filled with matching bricks.
- Every third course should be laid straight.
- All vertical joints must be accurate.
Facing brickwork shall be securely bonded to the backing bricks or concrete using approved anchor ties as needed and should not be built more than 600mm ahead of the backing bricks or concrete at any time.
10. Traffic signals
All traffic signal equipment shall be supplied and installed by us. This is to ensure that the equipment is compatible with existing traffic management control systems, monitoring equipment, associated systems database programming and validation. This will also ensure that equipment is to the correct specification and can be included in existing maintenance regimes.
We will provide a quotation for the supply and installation. Full payment shall be made prior to commencement of works to allow procurement of the required equipment.
A minimum of 16 weeks shall by required between placing the order and installation of equipment in the public road. This lead in time should be factored into works programmes.
11. Seeding and planting
Where roadside planting or sustainable drainage system is proposed for adoption, it is important to ensure planting and biodiversity will be established.
Topsoil
Topsoil is the top layer of soil which can support plant growth and contains a mixture of organic material and nutrients, and shall be removed from the area the road or footpath is built on and should be stockpiled for re-use. Imported topsoil shall be Class A multipurpose in accordance with BS 3882 Clause 4.1.
For sustainable drainage systems a mixture of 70% sand and 30% topsoil shall be at the base, known as the root zone. The topsoil shall in accordance with BS 3882:2015 and the sand shall meet the following requirements:
- The rate at which water passes through when saturated, known as saturated hydraulic conductivity, to be greater than 220mm per hour.
- The ratio of voids to the total volume to be greater than 30%.
- An acidic value of 6.5 to 8.5 pH.
- Graded to:
- 5.00mm sieve with 89% to 100% passing.
- 2.36mm sieve with 65% to 100% passing.
- 0.30mm sieve with 5% to 50% passing.
- 0.063mm sieve with less than 4% passing.
Topsoil shall be added to the side slopes of cuttings, embankments, and verges and compacted to create a level surface, ensuring a minimum compacted thickness of 150mm. This will serve as a preparation for seeding or turfing and the process involves treading and raking the area in various directions.
Wildflower and Grass Seed Mix
Grass seed from an approved manufacturer, shall be spread at a total rate of greater than one kilogram to 50 square metres. Grassed areas shall be maintained in order to control weed growth.
SuDS embankments and bases should include a seed mix with an appropriate wildflower perennial and a minimum of 70% native wildflower.
SuDS filter strips and non-SuDS applications should be made up from 25% Barkoel Crested Hairgrass, 20% Hardtop Hard Fescue, 35% Barpearl Slender Creeping Red Fescue and 20% Bargreen Chewings Fescue.
Before sowing, all surfaces to be grassed should be reduced to a fine state, known as tilth. Stones larger than 20mm in diameter and all harmful materials shall be removed. Fertiliser from an approved manufacturer may be used, made up of part nitrogen, potassium and phosphorous to a ratio of 10:15:10.
Turfing
Turf in accordance with BS 3969:1998+A1:2013 shall be laid on the topsoil within three days prior to cutting between the 1st of April and 31st of August, or within one week prior to cutting during the rest of the year. The turf shall be clean, strong, well-bonded, and lightly beaten. Turf should be laid diagonally across the side slopes.
Planting
Additional evergreen or perennial planting along the roadside such as areas of bulbs and low maintenance shrubs will be assessed on a site-by-site basis.
New Trees
Trees shall be over 1.5m in height and a minimum 8cm girth, with planting carried out between in early November and March.
The species and variety should be diverse and suited to the soil type, space available and growing conditions. An indicative list is provided by us however alternative species may be proposed.
A tree pit shall have a minimum size of 450mm long, 450mm wide, and 300mm depth with loose soil in the bottom of the pit and 50cm deep mixture of organic material at the surface.
The positioning of tree planting should consider the height and spread. Trees should not be planted within two metres of buildings or five metres of street lighting columns, if this is the case the street lighting column should be repositioned.
Root Barriers shall be required around tree pits where trees are planted within five metres of roads and footpaths. A proprietary, high strength, photo and bio degradation resistant root barrier should be used. This shall be two millimetres thick with a minimum width of one metre.
Where individual trees are to be planted, the use of preformed root directors may be more appropriate.
Retained Trees
Existing trees that are retained alongside the road or footpath shall be protected in accordance BS 5837 for the duration of construction.
The rooting area shall be protected from compaction, excavations and contamination so that they remain viable and in good condition.
12. Species of planting
Wildflowers
The following species are acceptable for sustainable drainage systems:
- Betony
- Devils Scabious
- Musk Mallow
- Oxeye Daisy
- Purple Loosestrife
- Red Campion
- Salad Burnet
- Selfheal
- White Campion
- Common Knapweed
- Common Sorrel
- Creeping Buttercup
- Ladys Bedstraw
- Meadow buttercup
- Meadowsweet
- Ragged Robin
- Wild Carrot
- Wild Red Clover
- Yarrow
Grasses
The following species are acceptable for sustainable drainage systems:
- Creeping Bent
- Meadow Foxtail
- Sweet Vernal Grass
- Crested Dogstail
- Slender Creeping Red Fescue
- Smoothstalked Meadowgrass
- Quaking Grass
- Slender Creeping Red Fescue
Mixture of trees
To ensure future-robust tree populations, no more than 30% of the trees along a road and footpath should be one species or variety. Where there is sufficient space, larger trees provide more environmental benefits than small trees.
Small trees
Suitable for narrow verges and five metres from streetlights:
- Native to UK, high value to wildlife:
- Betula pendula Fastigiata
- Crataegus laevigata Paul's Scarlet
- Crataegus monogyna Common Hawthorn
- Fagus sylvatica Dawyck Fastigiate Beech
- Prunus padus Bird cherry
- Quercus robur Fastigiata (Koster)
- Fastigiate, very narrow crown:
- Acer campestre William Caldwell
- Acer lobelli Lobel's maple
- Betula pendula Fastigiata
- Cupressus sempivirens Italian Cypress
- Fagus sylvatica Dawyck Fastigiate Beech
- Ilex aquifolium Holly
- Malus sylvestris Crab Apple
- Prunus Amanogawa
- Pyrus calleryana Chanticleer, Chanticleer Pear (over-used, alternative preferred)
- Quercus palustris Green Pillar
- Quercus robur Fastigiata (Koster)
- Ulmus carpinifolia Wredei Aurea, small elm
- Narrow trunk, suitable for base of swales and narrow SuDS features:
- Nyssa sylvatica - Black Gum tree
- Other small trees:
- Acer campestre Arends
- Acer campestre Elegant
- Acer campestre Elsrijk
- Amelanchier arborea Serviceberry
- Amelanchier lamarckii Serviceberry
- Arbutus unedo Strawberry tree
- Betula ermanii
- Crataegus lavalleei Hybrid Cockspur Thorn
- Crataegus x prunifolia Broad-leaved Cockspur Thorn (thorny)
- Malus huphensis Hupeh Crab Apple
- Malus Rudolph
- Prunus cerasifera Myrobolan Plum
- Prunus x Hillieri Spire
- Prunus Kanzan
- Prunus sargentii
- Prunus x subhirtella Autumn Cherry
- Prunus Umineko
- Sorbus aucuparia Asplenifolia
- Sorbus aucuparia Cardinal Royal
- Sorbus aucuparia Edulis
- Sorbus aucuparia Sheerwater Seedling
- Sorbus huphensis
- Tamarix tentrandra Tamarisk (tolerant of salt winds and soils)
- Tilia mongolica Mongolian Lime
Large trees
Suitable for open spaces and greater than 10 metres from streetlights:
- Native to UK, high value to wildlife:
- Acer campestre Field maple
- Alnus glutinosa, Common Alder
- Betula pendula Silver birch
- Betula pubescens Downy birch
- Carpinus betulus Hornbeam
- Fagus sylvatica Common Beech
- Pinus sylvestris Scots Pine
- Populus tremula Aspen
- Populus tremula Erecta
- Prunus avium Wild cherry (unsuitable for paved areas, large surface roots)
- Quercus petrea Sessile oak
- Quercus robur English oak
- Salix caprea Goat willow or sallow
- Sorbus aria Whitebeam
- Sorbus aucuparia Rowan
- Tilia cordata Small-Leaved Lime (can drip sap)
- Tilia x europaea Common Lime (typical of Victorian streets, often pollarded, can drip sap)
- Taxus baccata Yew (common in churchyards, dark, poisonous berries)
- Tilia platyphyllos Large-Leaved Lime
- Fastigiate, very narrow crown:
- Populus nigra Italica Lombardy Poplar (vigorous)
- Populus tremula Erecta
- Narrow trunk, suitable for base of swales and narrow SuDS features:
- Alnus glutinosa, Common Alder
- Betula nigra River birch
- Tolerant of waterlogged soils, suitable for swales:
- Alnus cordata Italian alder (vigorous surface roots, best for unpaved)
- Alnus glutinosa, Common Alder (tolerant of flooding, suitable for swales)
- Alnus incana Grey alder (tolerant of poor soils)
- Betula nigra River birch (good for wet site such as swales)
- Populus tremula Aspen (vigorous, good for wets sites)
- Populus tremula Erecta
- Salix caprea Goat willow or sallow
- Taxodium distichum Swamp Cypress
- Other large trees:
- Acer negundo Box elder
- Acer platanoides Norway maple
- Acer pseudoplatanus Sycamore
- Aesculus x carnea Red Horse Chestnut
- Ailanthus altissima Tree of heaven
- Betula albosinensis Fascination Chinese Birch
- Betula papyrifera Paper birch
- Betula utilis Himalayan birch
- Carpinus betulus Fastigiata
- Castanea sativa Sweet Chestnut
- Catalpa bignonioides Indian Bean Tree
- Cedrus atlantica Atlas Cedar
- Cedrus deodara Deodar Cedar
- Cedrus libani Cedar of Lebanon
- Celtis australis Nettle Tree
- Corylus colurna Turkish Hazel
- Ginkgo biloba Maidenhair Tree
- Gleditsia triacanthos Honey Locust
- Juglans nigra Black Walnut
- Juglans regia Common Walnut
- Larix decidua Common Larch
- Liquidambar styraciflua Sweet Gum
- Liriodendron tulipifera Tulip Tree
- Metasequoia glyptostroboides Dawn Redwood
- Ostrya carpinifolia Hop Hornbeam
- Pinus nigra Austriaca Austrian Pine (large pine tree useful for coastal locations)
- Platanus x hispanica London Plane (very large, tolerant of air pollution)
- Platanus orientalis Oriental Plane (large, decorative)
- Quercus ilex Holm oak, evergreen
- Quercus rubra Red oak
- Robinia pseudoacacia False acacia
- Robinia pseudoacacia Frisia, yellow form
- Salix alba Tristis (x sepulcralis Chrysocoma) Golden Willow, weeping
- Sequioadendron giganteum Wellingtonia or Giant redwood (very vigorous)
- Sequioa sempivirens Coastal redwood (very vigorous)
- Sorbus intermedia Swedish Whitebeam
- Sorbus thuringiaca Bastard Service Tree
- Thuja plicata Western Red Cedar
- Tilia cordata Greenspire uniform, columnar form
- Tilia cordata Rancho, compact form
- Tilia x euchlora Caucasian Lime (does not attract aphids so does not drip sap_
- Tilia tomentosa Silver Lime
- Ulmus lutece Elm (resistant to Dutch Elm Disease)
- Ulmus Clusius Elm (resistant to Dutch Elm Disease)
- Ulmus Lobel Elm (resistant to Dutch Elm Disease)
- Zelkova serrata
- Zelkova serrata Green Vase, columnar form
Trees not suited to urban areas
- Native to UK, high value to wildlife:
- Populus alba White Poplar (fast-growing tree with invasive roots)
- Sorbus torminalis Wild Service Tree (native tree prefers shaded location)
- Tolerant of waterlogged soils, suitable for swales:
- Populus alba White Poplar (fast-growing tree with invasive roots)
- Populus nigra Black Poplar (fast growing and large, needs space)
- Other unsuitable trees for urban areas:
- Acer cappadocicum (tends to produce suckers)
- Acer rubrum Canadian maple (prefers acid soils)
- Acer saccharinum Silver maple (fast-growing and brittle, needs lots of room)
- Aesculus hippocastanum Horse chestnut (affected by several pests and diseases)
- Laburnum anagyroides Laburnum (decorative flowering tree, poisonous)