Important Permeable paving installation notice:
The permeable system should not be attempted by the DIY enthusiast or untrained installer.
It requires the careful calculation of a soil permeability test and appropriate use of specially graded sub-base aggregates The permeable 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% and should be laid with a 20mm and 6mm washed aggregate.
Conditions required for permeable surfaces
The grade of permeable blocks featured in this blog is only intended for normal domestic vehicles and pedestrian traffic, though occasional delivery vehicles over 3.5tonnes gross weight can be tolerated. The domestic permeable system is only intended for driveways or paths where infiltration is required only in the immediate permeable paved area and not from other surrounding paved or roofed areas. 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. Properties constructed pre 1920 may not have been built on traditional concrete foundation, therefore, if this is proved to be correct during excavation then the permeable system should not be installed. Check for services, permeable paving must NOT be installed if gas or electric services run through intended permeable areas.
Guidelines for Installing Permeable Block Paving Surface Gradient
The intended permeable area must fall away from the owner’s house and any other buildings in the immediate vicinity. If the driveway exceeds 20m in length and/or has a gradient greater than 1 in 100 then please contact me to discuss the installation of baffles. The top surface of the driveway should finish at least 150mm below any adjoining wall DPC level.
Existing Foundations
If your house lies adjacent to or less than 600mm from the proposed permeable driveway area, establish depth of house foundation before undertaking any soil test/permeable installation. The house foundation top surface must be 600mm (minimum) below the finished level of the top of the proposed permeable driveway.
Soil Strength and Permeability
All permeable systems must be laid on a subgrade which has previously had an established and adequate existing driveway and an area which has a subgrade soil strength greater than 5%. The permeable 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 permeable area.
Discharge onto Roadway
The surface area must not discharge onto surrounding public roadway, pathways at all.
Rain Water Catchment Area
No adjoining surface areas (rainwater pipes, roof areas etc) must drain onto and into the proposed permeable driveway area, however, small areas such as door steps and garage areas are acceptable providing they do not exceed 5% of the driveway area
Aggregates
All permeable units must be laid with 20mm and 6mm washed graded angular aggregate to BS EN12620 to ensure compliance.
Trees
When installing in close proximity to existing trees, tree roots smaller than 25mm diameter may be 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 Reroot 1000 root barrier or similar which is non surface protruding, and therefore, does not present a trip hazard once installed.
Health and Safety
It is possible that more excavation for a permeable 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, Permeable paving must not be installed if gas or electric services run through intended 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.
