Outdoor channel drainage

Outdoor drainage channels with removable gratings or continuous slots. Linear drainage systems are designed to remove surface water from pavements, roads and driveways quickly and efficiently. Slot drains are relatively quick, easy and economical to install and maintain. Shallow construction and minimal excavation avoids the need for gullies or buried pipes required by point drainage systems.

Drainage channels may incorporate an internal or external fall or slope, or have a constant depth.

Manufacturers champion different shapes and designs. Some are designed for optimal water flow, others minimise silt settlement, and some materials encourage self-cleansing movement.


Performance / load classes

External channel drainage is specified for areas subject to pedestrian or vehicular traffic, and is rated according to the load classes set out in BS EN 1433:2002 for drainage channels set in trafficked surfaces.

 Class Load Applications
A15 15kN Residential, light pedestrian and cycle traffic
B125 125kN Public footpaths, pavements and small private car parks
C250 250kN Kerbsides, car parks, hard shoulders and general commercial areas
D400 400kN Carriageways, trafficked sections of roads and highways
E600 600kN Industrial areas, petrol stations and light commercial forklifts
F900 900kN Aircraft pavements, docks, heavy forklift trucks and abnormally heavy wheel loads








Product types / variants

Drainage channels with removable gratings

Removable grating channels have functional galvanised steel grids or solid covers, ornate cast iron gratings, or high-specification resin polymer or stainless steel fittings. In many cases, the grating itself is a design feature, which will integrate well with paved surfaces in public spaces or commercial developments, and complement other building products and architectural elements. Channels with fixed, integral gratings, which provide a high level of vandal-resistance, are also available.

Slotted linear drains

Slotted linear drains integrate especially well with natural stone or concrete block paving schemes, and, in some cases, can be fitted right alongside building facades. The single continuous slot is unobtrusive yet effective in removing surface water quickly without ponding.



Civic / industrial applications

Channels for civic and industrial surface water drainage infrastructure include products for roads, pavements, car parks and transport terminals through to stockyards, airports and military sites.

Residential applications

Channels for residential applications include pathway, patio, driveway and threshold drains.

Other applications

Distinct products are also available for combined drainage kerbs and sports channel drains.

Designs that integrate lighting fixtures are also available for low level lighting of paved areas.


Composition and manufacture


Galvanised steel, stainless steel, cast or ductile iron are some of the materials used for gratings and slots.

To provide the best appearance for a project and to handle the necessary direct traffic loadings, the construction of the main body of the subsurface channel is also critical to its fitness for purpose.


GRP (glass reinforced plastic), polyethylene, polypropylene channels are especially lightweight, easy to transport, and quick to install. They are resistant to abrasion, frost, rust, hot asphalt and chemicals, and strong enough to prevent damage during site handling. They tend to be suitable for light-duty applications.

Polymer concrete

Proprietary polymer concrete channels can be 75% lighter than traditional concrete channels. Again, they are resistant to frost, chemicals and road salt. Steel edge supports can reinforce the strength of the channel.


GRC (glass reinforced concrete) channels have a high strength-to-weight ratio and are resistant to damage, whether from frost, chemicals, road salt or during handling.


Technical data


External channel drainage elements typically come in standard lengths of 500mm or 1000mm. Some product ranges include elements as long as 1500mm or 2000mm, which can help with the quick installation of longer runs of drainage.

Nominal internal widths tend to range from 100mm up to 900mm for very high capacity channels.

Specially designed shallow channels can be specified for sites where excavation is restricted.

See also