Even a self-build needs the right drainage, to avoid flooding. Take a look at our Soakaway Types page to learn about the different types of soakaway and which types of project they are best suited for.

Geological maps can often give us clues as to whether different types of soakaways work, but these maps aren’t wholly accurate and the subsurface can be highly variable. The only way to be 100% certain is to conduct soakage testing at various depths.

Use the 1 day BRE365 soakage test. We cant guarantee the test wont work, but the one-day soakage test according to BRE365 will prove that the ground conditions are unsuitable for a soakaway due to the failure of the test, this is noted by the water not falling by 50% over a 24 hour period. If the level of the water barely changes over a period of several hours, the test will be abandoned due to the impermeable soils. While we cannot guarantee that the test definitely won’t work, this form of the test is done in cohesive soils to prove their impermeable nature.

The one-day soakage test is carried out in cohesive or impermeable soils in order to prove their unsuitability for soakaway construction. A full BRE365 soakage test involves 3×24 hour soakage tests in the same pit to be carried out. As such, the full test requires four days of on-site monitoring. This provides data which is then used to calculate the percolation rate of the soil, which is then subsequently used in soakaway design. 

BRE365 Soakage Test

A BRE365 soakage test is in essence a hole that is dug in the ground and then filled with water. The hole needs to be 0.3m to 1m wide, 1.5m to 2.5m deep, and 1m to 3m long. They are almost always mechanically excavated, digging them by hand is very tiring and pretty much a waste of time. After the hole has been dug a water bowser or IBC filled with water (usually around 1000 litres of it) is towed up to the hole and emptied into it. The depth of the pit and the depth to water are recorded. Once the pit is full the timer is started and over a course of 24 hours 5 to 10 readings of the height of the water are taken. If the test was a success, so at least 50% of the water ran from the hole, the test is repeated 2 more times – this takes four days altogether, hence the “four-day test”. The averages of the readings are then taken, and the percolation rate of the soil can be calculated. If 50% of the water did not run away the test failed and the soil is largely impermeable – this takes either the full 24 hours or is called early if the level does not change, hence the “one-day test”.

Infiltration Rate 

The rate of infiltration is a measurement of the speed or velocity that water enters the soil. Typically, the infiltration rate is determined by the depth (in mm) of the layer of water that can penetrate the soil over the span of an hour. If an area of soil had an infiltration rate of 20mm/hr this would mean that it would take one hour for a 20mm layer of water on the surface to fully infiltrate the soil. 

Percolation Rate 

The speed at which the water dissipates through an area of soil is known as the soil’s percolation rate. A percolation test (sometimes referred to as a perc’ test), tests the rate at which water moves through an area of soil. A professional percolation test is a vital step to take before the construction of any soakaway as it helps you decide on the size and type of soakaway that your site requires.

Subsidence Risk 

Subsidence happens when the earth under your building begins to sink. As the ground falls lower, it may misalign the foundations of your home. When the ground under your property sinks at various rates it is especially troublesome and cause damage to both the structure and foundations of your building. Leaking water from drains, faulty soakaways or water mains can significantly increase the risk of subsidence.