What a soakaway does and when you need one
Rainwater from a roof, patio or hard surface has to end up somewhere, and a soakaway returns it to the ground on your own property. You may need one when a new patio or extension adds hard surface, when a garden drain needs an outlet, or when a downpipe currently empties onto the lawn. Non-permeable driveways are another common reason, because rain must not run onto the road. Soakaways are designed for surface water only. Foul water from toilets, sinks or washing machines must never go into one, as it would contaminate the ground.
- Roof downpipes with no drain connection
- New patios and hard landscaping
- Outlets for land drains and French drains
- Non-permeable driveways on a front garden
The percolation test comes first
Whether a soakaway will work depends on how quickly the ground absorbs water, and that can only be found by testing. A trial hole is dug to the depth planned for the soakaway, filled with water, and timed as the level drops. The test is repeated, because the first fill often drains faster than wet ground will in practice. The results also show how big the soakaway should be for the area draining into it. BRE Digest 365 is the recognised method for this. A test in a dry summer can flatter the ground, so winter conditions should be kept in mind.
- Dig a trial hole at the proposed depth
- Fill it with water and time the drop
- Repeat to see how wet ground behaves
- Use the results to size the soakaway
Where a soakaway can go
Position matters as much as size. Building Regulations guidance says a soakaway should generally be at least 5 metres from a building or road, so that water does not undermine foundations. It should also be away from boundaries, in ground free of contamination, and not on unstable land or where the water table rises to its base. That rules out some small gardens and tight yards altogether. Before digging, check for pipes and cables, and keep clear of tree roots. If a building is close by, or the extension is under Building Control, get their sign-off on the design.
- Generally 5 metres or more from buildings and roads
- Well above the highest seasonal water table
- Away from boundaries and neighbouring land
- Clear of services, pipes and tree roots
Crates or rubble: which type of soakaway?
The traditional soakaway is a pit filled with clean stone or broken hardcore, and it still works in the right spot. Modern plastic crates are wrapped in a permeable geotextile and buried in the same way. Crates hold much more water for their size, since they are mostly empty space, so the excavation can be smaller. Rubble takes up much of the pit, which leaves less room for water. Either type needs a filter, such as a catchpit or silt trap, so that leaves and grit do not reach the soakaway and slowly choke it.
- Crates: more storage in a smaller hole
- Stone-filled pits: simple, traditional and robust
- Geotextile wrap to keep soil out
- Silt trap to make maintenance simple
What if your soil is clay?
Heavy clay is the most common reason a soakaway fails, because water sits in the pit and has nowhere to go. It can leave you with a hidden underground pond, and water may back up into the garden when it rains. If the test shows poor results, the answer is usually to reduce the amount of water going in, or use another route. Permeable paving, rain gardens or a water butt can help. Connecting to a surface water drain may be an option, but that will need approval from your water company.
- Permeable surfaces that deal with rain where it falls
- Rain gardens and planted areas
- Water butts to capture roof water
- Connection to a surface water sewer, with consent
How we approach soakaway installation
We usually install soakaways as part of a bigger job, such as a new patio, a garden drainage scheme or a driveway. Sean will look at your site, talk through testing and tell you plainly if a soakaway is not the right answer for your ground. Then we dig out, fit the soakaway, connect the pipework, reinstate the surface and take the spoil away. Because we do the landscaping too, the lawn or paving above can be finished properly afterwards. For a free visit in Pontefract or across West Yorkshire, call 07860 510073 or send us an enquiry.