Stonemarket are introducing PermeaPave, the first permeable concrete block paver to its range.
Why a permeable block paver?
Traditionally, construction of a hard surface i.e. a domestic driveway, has been to install a non-permeable surface and collect rainwater in a drainage channel or gully and carry the surface water to source e.g. existing pipework leading to sewer system/soft planting. In some instances, domestic properties allowed surface water to drain off into the adjoining roadways. In October 2008, changes to the English Building Regulations were made to ensure that surface water is not discharged from domestic properties onto roadways, hence the public sewer. This in the main applies to paving over front gardens to provide a hard standing for vehicle parking. As our built environment increases, our natural drainage methods are reduced, in addition climate change is causing adverse weather conditions. The result is greater instances of flooding as our systems overflow, this is being seen not just in the UK but globally. Dealing with surface water at source can be done in one of two ways; Installing PermeaPave Concrete Block Paving i.e. a permeable system allows rainwater to pass through the joints of the block paving into a specially designed sub-base will the ability to store this surface water. This water then slowly filters into the underlying earth and recharges natural water tables. This method mimics natural drainage, the quickest method to deal with removal of surface water and prevent flooding. Encouraging filtration into the ground is seen as best practice, Sustainable Urban Drainage Systems (SUDs) are becoming common practice and alleviates pressure on our existing pipe drainage network. Preventing discharge onto highways is only the first stage to best practice becoming legislation. SUDs methods deal with rainwater at source and are the most effective methods in dealing with rainwater intensity whose pattern is rapidly moving as our climate changes. Secondly, installing a non-permeable surface material i.e. Pavedrive Concrete Block Paving and collecting the surface water which can then be discharged into soft landscaping or a soakaway and encouraged to filter into the ground. For further clarification on where the aforementioned legislation is a requirement please refer to the Governments Planning Portal www.planningportal.gov.uk/suds.
This document deals with the installation of Stonemarket PermeaPave which is a Permeable Concrete Block Paver.Guidelines for the flexible installation of Stonemarket PermeaPave concrete block paving in domestic situations
These guidelines cover the construction of modular permeable pavements using Stonemarket PermeaPave concrete block paving and are in accordance with Interpave’s (The Precast Concrete Paving and Kerb Association) document ‘Permeable Pavements; ‘Guide to the Design, Construction and Maintenance of Concrete Block Permeable Pavements (Edition Five, December 2007)’.
2.0 Products Included
Stonemarket PermeaPave concrete block paving of 60mm nominal thickness, is manufactured in accordance with BS EN1338: 2003 (Concrete paving blocks – Requirements and test methods).
3.0 Health and Safety Information
Safe working practices should be employed at all times during the construction process. All relevant health and safety information, including COSHH data sheets can be obtained from www.stonemarket.co.uk
4.0 Pavement Design
Stonemarket PermeaPave permeable paving system should be laid on to a compacted open graded crushed rock granular sub base of 200mm minimum depth on a sub grade of minimum 5% CBR or which has previously had an established and adequate existing driveway. For assessment of CBR (California Bearing Ratio) please see Page 11.
5.1 Material Selection
5.1.1 Sub-Base Material
Open graded materials are required to allow storage and percolation of the surface water within the pavement construction. The Open Graded Crushed Rock (OGCR) or Open Graded Crushed Gravel (OGCG) sub-base should have no fine material present to cause blocking of the voids. The material should meet the grading requirements as shown in Table 1. Due to the relationship between the grading curve of the OGCR or OGCG sub-base material and the laying course material, a geotextile between these layers may not necessarily be required.
- 5.1.1 Sub-Base Material
5.2 Construction Considerations
Sub-base material should be placed in layers not exceeding 150mm in thickness or twice the nominal maximum aggregate size. Unlike traditional pavement construction, the open-graded materials should not be fully compacted to eliminate any voids, as this will compromise the performance of the system. It is likely that excessive compaction will result in the displacement of the open- graded aggregate by the compaction equipment. The open-graded material should be compacted such that its maximum density is achieved for the particular aggregate type and grading without compromising the final voidage offered by the material. Each layer should be suitably compacted before the next layer is placed to prevent any potential settlement of the pavement after completion. Due to the nature of both the sub-layers and the block paving care should be taken during the construction process to prevent dirt or detritus contaminating the sub-base and compromising the permeability of the system. For example, the trafficking of the sub-base as a site access route should not be undertaken. Should other construction or maintenance work take place close to the pavement which may affect the infiltration of the pavement, suitable protective measures should be taken.
To allow the new permeable block paving to be installed correctly a certain amount of excavation is required. The depth of excavation is based on the thickness of the sub-base required (minimum 200mm) plus the laying course and block pavers (110mm). An important factor to consider when working out the depth of excavation is that the finished surface level of the blocks, when being laid up to an existing structure, must be a minimum of 150mm below the DPC to prevent any potential problems with rising damp.
- 5.1 Material Selection
6.0 Edge Restraints
Edge restraints should be sufficiently robust to resist the lateral displacement from imposed loadings placed upon the pavement. The edge restraint may take the form of associated fittings, walls or buildings or be formed from precast concrete, clay or natural stone kerb systems, either existing or newly constructed features. The restraint must provide a consistent vertical face to a level below the laying course material.
Modular edge restraints systems should be laid onto a suitable base of sufficient strength to withstand vehicular over-run. Units may be mortared to the suitable base and incorporate either a mortar joint, or narrow gap of trowel width. The surface course of the pavement should not be vibrated until such time the edge restraint has gained sufficient strength to resist the lateral imposed loads. Where mortar bedding and jointing is adopted, consideration should be given to the provision of movement joints at regular intervals. Where an intermittent restraint may be required, the edge restraint’s base material may be laid directly onto the open-graded sub-base material. Should any concern exist about the restraint bedding material compromising the voidage of the open- graded sub-base material, a suitable lining material can be used, separating the two materials.
- 6.1 Construction
7.0 Laying Course
7.1 Materials Selection
The large size of sub-base material aggregate creates an uneven surface when compacted and has an open textured surface. The laying course material provides a flatter platform onto which the blocks are laid, to prevent any rocking or instability of the blocks in-situ.
Baffles are intermediate concrete barriers used on sloping sites to prevent the water flowing to the bottom of the slope and collecting there and subsequently coming out the joints between the blocks. For further information regarding the requirement for baffles please refer to Page 14.
- 7.1 Materials Selection
8.0 Wearing Course
Paving units should be laid on the laying course material so that the final level is within the permitted surface tolerance. String lines should be utilised as often as required. This is necessary to ensure the bond pattern is maintained and straight lines are achieved in the finished paving. The manufacturing tolerances of the paving units, profile of the site and frequency of string lines used should be taken into consideration during laying. These factors may have a bearing on the straightness of line achievable. Paving units should be laid such that the joint profile interlocks with its neighbouring units. Joint widths may be varied slightly in order to achieve straight lines or maintain bond. When laying block paving, the blocks should be mixed simultaneously from a minimum of three packs, taking vertically from each slice offered by the pack. This is necessary to ensure an even distribution of both the colours and any manufacturing tolerances offered by the blocks. Lay whole paving units first, followed by cut units around obstacles or at edges. No paving unit should be cut down to less than one quarter of its original size to prevent looseness or dislodgement at a later date. Where it appears that only a small section of block will fit, the “inboard cutting” technique should be adopted. The use of a larger or full unit against the edge restraint, allows a smaller unit to be placed in the resulting space. Where slopes, gradients or ramps are being constructed, placement of the paving units should commence at the lowest point i.e. the bottom of the slope, working upwards. Where there is a risk of lateral movement of the paving units due to the gradient encountered, the provision of additional intermediate restraint should be considered.
Compaction should be undertaken with a plate vibrator, conforming to the requirements of Annex F of BS 7533: Part 3: 2003. Prior to final compaction of the surface, joints should be filled with the same grading of material as that used for the laying course. All joints should remain full of jointing material at all times, with periodic checking and replacing carried out where necessary.
The bond pattern should be decided between the contractor and client prior to works being undertaken, and should be suited to the application and likely use of the pavement. Typically for domestic driveways either a herringbone 45 or 90 degree or a stretcher pattern is used.
- 8.1 Laying
Cutting may be carried out using a diamond tipped power saw, a block-splitting guillotine, or hammer and bolster. It must however be noted that the aesthetic finish achieved will depend greatly upon the choice of cutting mechanism and the skill of the installer. Cut blocks should be inserted prior to completion of the working period to prevent any movement of unrestrained blocks. Blocks should be cut such that the resultant joint width remains within the 2 – 6mm tolerance. When laying to tight curves it may not always be possible to maintain a maximum 6mm joint, in which case, cut or special shaped units may have to be considered.
All necessary Personal Protective Equipment (PPE) should be worn on site, as the site rules dictate. Both the operator of the cutting machine and any person within its immediate vicinity must always wear goggles, ear protection, dust masks and protective footwear, whenever cutting operations are undertaken.
In brief, Stonemarket would recommend:
- Inspect at least twice a year, spring and autumn and/or after a major storm. • Brush the surface to remove debris and encrusted sediment.
- Maintain area to be free of vegetation.
- Replenish joints when empty (20kg bags available).
- Ensure the owners are aware of the pavement construction and the do’s and don’ts of the system.
Stonemarket advise against the use of any traditional sealant on a PermeaPave system. Due to the nature of the pavement this may, for example, dramatically reduce the infiltration rate of the blocks and the sub-layers.
13.0 Further Information
- BS EN1338: 2003 Concrete Block Paving – Requirements and test methods.
- BS7533 - 3: 2003 Code of Practice for laying concrete paving blocks and clay pavers for flexible pavements.
- BS7533 - 11: 2001 Code of practice for the maintenance and reinstatement of pavements of concrete, clay and natural stone.
- BS EN13242 A1: 2002 Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction.
- Interpave Permeable Pavements; Guide to the Design, Construction and Maintenance of Concrete Block Permeable Pavements (Edition Five, December 2007) www.paving.org.uk
- Environment Agency – Guidance on the permeable surfacing of front gardens www.environment-agency.gov.uk/suds
- Royal Horticultural Society – Gardening Matters, Front Gardens. www.rhs.org.uk
- DCLG – Planning Portal www.planningportal.gov.uk/suds
The advice given above assumes the use of Stonemarket products. If you use any other manufacturer's products, Stonemarket can accept no responsibility whatsoever for the performance of those products or generally for the advice it has given. As Stonemarket are not involved in the overall design, management and supervision or the selection of materials or contractors, we cannot be liable for the performance of our products on site and in use. This does not detract from the customers rights under common law for claims made against the quality of our products should the situation arise.
PermeaPave – Conditions and Guidelines
Definition of scope
Please Note - In some parts of the country there are ground conditions where infiltration could adversely affect foundations to houses, therefore, if in doubt seek advice from a specialist or the local authority building control department.
PermeaPave is only intended for Domestic driveways, paths and patios which are subject to foot traffic or over run by typical domestic vehicles and vehicles that do not exceed a gross vehicle weight of 3.5 tonnes although occasional use by heavier delivery vehicles should not have a detrimental effect. The proposed construction depth of domestic PermeaPave is based on the standard design intended for Cars and Vans.
The Domestic PermeaPave system is only intended for driveways or paths where infiltration only is required in which the area must drain itself only and no other surrounding paved or roofed areas (see rain water catchment area guideline below). Check for services and contact the service provider for advice if gas or electric services run through intended PermeaPave areas. Stonemarket are not at this stage yet able to advise on attenuation systems, recycled water etc for domestic housing.
Properties constructed pre 1920’s may not have been built on traditional concrete foundation, therefore, if this is proved to be correct during excavation then Stonemarket PermeaPave system should not be installed. If the structure is built straight off the underlying material then the additional water being discharged via the PermeaPave may lead to instability.
Stonemarket PermeaPave system must be laid on a sub-grade which has previously had an established and adequate existing driveway and an area which has a sub-grade soil strength greater than 5%. Laying onto a sub-grade which has previously taken an established driveway proves that the sub-grade was able to take driveway construction + vehicle load over time. The standard designs are also based on conditions where the sub-grade is greater than 5%, therefore, this is being mirrored in our advice.
The PermeaPave system is only suitable for soil areas where infiltration applies and the test criteria have been met as per the standard permeability test. For the standard permeability, a test hole should be dug for every 20m2 of driveway. There should be a minimum of two holes. Holes/pits should be spaced evenly in relation to the proposed PermeaPave area. The soil test is key, if the sub-grade soil is not permeable then PermeaPave cannot be installed.
- The intended PermeaPave area must fall away from the owner’s house.
- The top surface of the driveway should finish at least 150mm below any adjoining wall DPC level. You must also ensure that the area falls away from all properties and building local to the intended area. If the intended PermeaPave system falls towards the house, then depending on the gradient water could discharge and pool in and around areas of the house structure, this could lead to damp areas appearing on the masonry leaf, flooded cellars...etc.
- In some instances the use of baffles is required. The table below refers to the number of baffles required; measuring the length of the fall (m), and the gradient of the area. Depending on the gradient in relation to the length additional construction processes will be required. In this case the provision of baffles.
Discharge onto Roadway
The PermeaPave area must not discharge onto surrounding public roadway and pathways and towards any buildings. Regulations which apply to standard driveways.
If your house lies adjacent to or less than 600mm from the proposed PermeaPave driveway area, establish depth of house foundation before undertaking any soil test/PermeaPave installation. The house foundation top surface must be 600mm (minimum) below the finished level of the top of the proposed PermeaPave driveway. The foundation area must not be disturbed mechanically as the integrity of the building maybe affected over time. The level of water discharge must be above the level of the foundations to avoid instability at foundation level.
Rain Water Catchment Area
No adjoining surface areas (rainwater pipes, roof areas etc) must drain onto and into the proposed PermeaPave driveway area; however, small areas such as door steps and garage areas are acceptable providing they do not exceed 5% of the driveway area.
Guideline: Catchment area = driveway area
Catchment area = drained surface area. If other areas are drained in addition to the driveway area then the hydraulic calculation will lead the depth, thus increasing the proposed depth of 200mm for the 20mm open graded material.
When installing in close proximity to existing trees, tree roots smaller than 25mm diameter maybe pruned back, preferably to a side branch, using a suitable pair of secateurs or hand saw. Roots larger than 25mm should only be severed following consultation with an arboriculturist, as they may be essential to the tree’s health and stability. Protection of the pavement will also be required, hence the requirement of a permeable root barrier system such as the Geoweb bio barrier system (www.Fiberweb.com) or similar which is non surface protruding, therefore, does not present a trip hazard once installed. Integrity of the pavement installation and intended life maybe affected by the ingress of roots Root barrier diagram p.19
Total Pavement Thickness
PermeaPave block thickness 60mm Laying course depth 50mm Sub-base depth 200mm. Keep it simple, 1 standard design for applications where all the other criteria points are met.
Health and Safety
It is possible that more excavation for a PermeaPave driveway may be required than that of a driveway constructed of traditional block paving. Therefore, care must be taken when excavating ground to a deeper level. Particular care must be taken to protect the sites from children and partially sighted persons and for collapse of adjoining features such as boundary walls/fences. Check for services and contact the service provider for advice if gas or electric services run through intended PermeaPave areas. Care must be taken when constructing over sewer, rainwater pipes and water pipes to ensure that the services remain supported for their full length by undisturbed material and are surrounded on the remaining sides by a minimum of 150mm of 6mm material to protect the service. It is important that special care is taken when installing PermeaPave if services run through intended PermeaPave areas. The type and depth of pipes may vary depending on a number of factors such as type of service and age of house. Therefore it is recommended that the relevant service provider is contacted if services run through intended PermeaPave area.
Further advice on Domestic Permeable Pavements: Interpave site - www.paving.org.uk/pdf/rainpave.pdf
Soil Permeability – Based on the BRE Digest 365 test Procedure
Remove topsoil/paving material surface to expose sub-grade soil. Dig hole within sub-grade soil to the size shown within Fig 1.0, ensure that all sides and the bottom surface of the hole are trimmed and leveled accordingly. Fill hole with water and allow to drain away naturally – repeat this process 3 times – If the water does not drain away at all then the sub-grade soil does not have adequate permeability properties required for PermeaPave.
Fill the hole with water to 75% (300mm) of the excavated height (measured from the base). Make note of the time once the level has been reached (start the clock!).
If the water level is 100mm or greater (measured from the base of the excavation) after 18.5 hrs has exceeded then the sub-grade soil does not have adequate permeability properties required for PermeaPave, do not install. If the water level falls below the 100mm mark (measured from the base of the excavation) before 18.5 hrs has exceeded then the sub-grade soil does have adequate permeability properties and PermeaPave is suitable for application.
All pre test and test work must be carried out for every 20m2 of driveway. There should be a minimum of two holes, equally distanced throughout the intended area to be paved.
Due to the maximum length of time that the test may take, the time of day the test will be undertaken should be considered.