SEL Roof Water Attenuation
SEL Roof Water Attenuation is a complete Sustainable Drainage System (SUDS) that has been developed in line with current guidelines as set out by CIRIA, the Environment Agency and SEPA.
SEL have been a key player in the development of underground attenuation since it's first inception back in mid 90's, SEL have been involved with many CIRIA research projects and in fact SEL assisted Wavin in gaining their BBA certification on their Aquacell Unit. Below is a photo of an Aquacell test cell being installed by SEL at our Stormer Hill Works. SEL have developed and fabricate in-house an entire range of special components to allow a fully watertight hot air welded attenuation tank encapsulation.
SEL's innovative concepts to provide cost-effective source control suds drainage push the boundaries of tried and tested traditional drainage design methods, with many of these ideas being widely adopted across the industry such as shallow storage, pre-treatment of run-off, checkdams within permeable paving to deal with slopes and low-cost shallow, small diameter flow control chambers (see flow control chamber page)
Roof and Hardstanding Catchments
Most current drainage designs combine the run-off from roofs and hardstandings into a single end of line attenuation tank. This method does not adhere to the ideals of source control, it can worsen contamination issues with the emulsification of oils into surfacewater run-off and it concentrates silt deposits creating some serious potential costly maintenance issues.
SEL continue to promote solutions that incorporate micro-catchments and seperate roof run-off and hardstanding run-off i.e. car parks. There are a number of environmental benefits by doing this but the main one of interest to Developers and Contractors is the COST. Many cost comparisons of Traditional Vs SEL Source Control have shown significant cost savings when comparing the WHOLE surfacewater drainage scheme, not just the cost of the attenuation tank. SEL will undertake a review and cost comparison for you if you have a site that may benefit. Not all sites are suitable and a review can quickly establish this.
Encapsulation for Attenuation Systems
The SEL roof water attenuation system recognises the importance of ensuring the watertight integrity of attenuation systems where it is essential that fluids are to be kept within the roof water drainage underground storage system (e.g. where there is a potential of contaminants leaching into a protected aquifer or watercourse). SELflex 1.0PP membrane is a 1mm thick robust polypropylene weldable membrane which requires the joints to be fusion welded and subsequently air-tested. The jointing should be carried out by an experienced membrane welder. SEL offer a membrane welder installation service. The SELflex welded membrane is protected by SELtex HD300 geotextile protection layer with exceptional dimensional stability consisting of a woven polyester core reinforced with needle-punched outer layers. We recommend the protection geotextile is used where the engineer insists on a watertight system. If permeability rates are too low for full infiltration, but it is not essential to provide a watertight arrangement, you might consider our SELtex 160WP waterproof geotextile or SELtex Permafilter oil retaining treatment geotextile.
Encapsulation for Soakaway Infiltration Systems
If the surrounding soils to the SEL roof water attenuation system are permeable, you may consider allowing the collected roof water to infiltrate / soakaway in to the surrounding ground. The attenuation structure can either be wrapped in a SELtex HD300 geotextile or if there is a potential of contaminants within the surface water run-off we recommend using the SELtex Permafilter oil retaining, oil treatment geotextile.
To support architects, engineers and contractors in designing and installing the SEL roof attenuation system, our Design Services Department offers computer aided scheme design, hydraulic performance calculations and advice on installation. Supply and install packages are available for elements of the system.
Roof water attenuation consist of an underground water storage tank that holds excess water during periods of peak rainfall. The stored water is gradually released back into the local surfacewater drainage system or directly into a watercourse, reducing the risk of upstream and downstream flooding through surcharging of the sewer network.
Cromwell Building, Salford - Polypipe Bulk Tank Installation
- Complete Source Control SUDS solution for new build or retrofit development
- Provides treatment at source by gravity separation using downpipe catchpit chambers.
- Provides attenuation or infiltration at source Shallow construction, minimises residual excavated material
- Contributes to BREEAM ratings Satisfies designers’ risk assessments in accordance with CDM
- Reduces the requirement for large diameter chambers and pipes Improves water quality
- A practical solution for the retrofit of SUDS components into existing drainage schemes
- System components are manufactured from recycled material and are also recyclable and reusable Resistant to frosts, salts and hydrocarbons
Jennet's Park, Berkshire. A Persimmon Homes and Redrow Homes Site. This was the biggest Wavin Aquacell Installation in Europe. For more information, click here
Soakaway infiltration systems are designed to store roof water run-off until it can be gradually absorbed by the surrounding soils. Standard Seltex HD300 infiltration geotextile is normally used or if installed close to a sensitive aquifer or watercourse the Seltex Permafilter oil retaining and treatment geotextile would be used.