Twin-wall drainage pipe allows water to flow faster and is therefore more likely to keep itself clean than single-wall, corrugated drainage pipe. So claims Galway firm JFC, which manufactures CorriPipe. The pipe is made by a twin extrusion process, which forms two pipes and heat welds them together as they are formed. The outside wall is corrugated but the inside one smooth.

“This smooth internal wall ensures there is no build-up of silt or solids - they are washed down the pipe,” says David Curley, CorriPipe sales manager. “Studies have shown that you need a velocity of 0.5m/second to ensure that the pipe will clear itself of silt. JFC’s 4in Corripipe laid at a gradient of 1:100 will generate a flow rate of 0.75m/second and will carry over six litres of water per second, which is important during heavy downpours.”