Skeletank solutions for Attenuation with Impervious Surfacing

According to The Building Regulations 2000 H3, impervious surfacings should be ‘freedraining’ if possible i.e. paths, driveways or other narrow areas of paving should drain to, ‘pervious areas such as grassland’. If this is not possible, then the use of impervious surfacings should be explored. However, in many cases, impervious surfaces cannot be ‘freedraining’ and pervious surfacings are impractical. In these instances provision will need to be made to drain impervious surfaces to an underground drainage system.

The Skeletank range of modular products and design techniques provide solutions for using SuDS in conjunction with impervious surfacings, including the utilisation of the aggregate sub-base layers below the surfacings to provide storage if required (a suitable highly voided aggregate, such as Aggregate Industries SudsAgg or equivalent, should be used). When using this technique, increased volumes of storage can be accommodated by including components from our range of proprietary underground storage media as and where appropriate.

If you are seeking to encapsulate the aggregate layers below your impervious surfacings with more cost-effective geotextiles as opposed to impermeable membranes, then it may be possible to have this construction within 5m of building foundations, (although ground conditions should be thoroughly investigated to ensure their suitability for this).

View the fact sheet USING SUDS CLOSE TO BUILDINGS.

Impervious Pavement Design Incorporating Skeletank® Attenuation Units

Skeletank® attenuation units (SELH01001) are unique, pre-formed, high strength, fully sealed attenuation modules which can be utilised to provide shallow storage under trafficked or landscaped areas, either for temporary attenuation or for rainwater recycling.

Each Skeletank® unit comprises 8 HydroWMS Permavoid® HD sub-base replacement modules, housed in a rotationally moulded, watertight shell. HydroWMS Permavoid® HD  is a unique and patented system for the replacement of sub-base below both pervious and impervious surfacings. It is fully compliant with the requirements of BS7533-13:2009 Annex B, ‘Typical physical properties of replacement systems (geo-cellular) units’.

• Skeletank® units each provide 300 litres of storage and have integral inlets and outlets to connect to standard 100mm diameter pipework. Units can be conjoined in multiple orientations to provide flexibility when meeting required storage volumes in areas where space is restricted.
• The high strength of Skeletank® units allows them to be installed at very shallow horizons, typically within the aggregate layers below a driveway or patio. Their structure guarantees an ‘off-the-shelf’ watertight structure, without the need for expensive and time-consuming membrane works.
• The top of Skeletank® units  is open to allow venting and they are each supplied with a pre-cut sheet of geotextile to prevent the ingress of soil or aggregates.

Skeletank products shown in this example

SELH01001	SELH03001	SELH03002
SELH03003	SELH05002

Impervious Pavement Design Incorporating Skeletank HPDC Units

Skeletank HPDC Units provide designers with an ideal solution for diffusing rainwater into and out of permeable aggregate layers* below impervious surfacings. They are available in two modular sizes (see below).

Skeletank HPDC Units are fully compliant with the requirements of BS7533-13:2009 Annex B, ‘Typical physical properties of replacement systems (geo-cellular) units.

SELH02003 – 708 x 708 x 150mm deep, for catchments up to 100m2

SELH02001 – 2124 x 354 x 300mm deep, for catchments up to 250m2

If ground conditions are suitable then it may be possible to encapsulate the aggregate layers with HydroWMS 300 HD Geotextile forming a ‘leaky tank’ to keep costs to a minimum. However, if a fully sealed system is required then the aggregate layer should be encapsulated by HydroWMS Geomembrane, protected by HydroWMS 300HD Geotextile.

The aggregate layers beneath a pervious surface provide one level of treatment, which satisfies Section 2 of the optional Water Quality Criteria in Category 4 of The Code for Sustainable Homes and thus gains one additional credit (if required).

*Note: when using this technique a suitable highly voided aggregate – e.g. Aggregate Industries SudsAgg or similar – should be used

Skeletank products shown in this example

SELH02003	SELH03001	SELH03002
SELH05001	SELH05002

Impervious Pavement Design Utilising Aggregate Layers for Storage and Incorporating Skeletank HPDC Units to Supplement Storage Volumes

If the standard permeable aggregate layer beneath your impervious surface is not providing sufficient storage to meet volume requirements (usually due to low permeability of underlying subsoils), but increasing the depth of aggregate to provide more storage is a problem (e.g. because of high water tables, or other factors restricting excavation) then the larger of the two Skeletank HPDC Units (SELH02001) can be utilised within the aggregate layer to increase storage volumes, without increasing excavation depths.

SELH02001 – 2124 x 354 x 300mm deep

If ground conditions are suitable then it may be possible to encapsulate the aggregate layers with HydroWMS 300 HD Geotextile forming a ‘leaky tank’ to keep costs to a minimum. However, if a fully sealed system is required then the aggregate layer should be encapsulated by HydroWMS Geomembrane, protected by HydroWMS 300HD Geotextile.

The aggregate layers beneath a pervious surface provide one level of treatment, which satisfies Section 2 of the optional Water Quality Criteria in Category 4 of The Code for Sustainable Homes and thus gains one additional credit (if required).

*Note: when using this technique a suitable highly voided aggregate – e.g. Aggregate Industries SudsAgg or similar – should be used
Skeletank products shown in this example

SELH02003	SELH03001	SELH03002
SELH02001	SELH05001	SELH05002
SELH05003

Note: Specification options for Geotextiles are a choice of either SELH05002 HydroWMS Permatex HD 300 Geotextile or SELH05003 HydroWMS Permafilter Geotextile.