What are soakaway crates and why should I be using them?
Rainwater soakaway systems are a traditional way of disposing surface water from buildings. Soakaways are probably the most common form of surface water disposal and have previously been a primitive system of filling a hole in the ground with coarse stone, this allows surface water to run back into the earth close to where it falls. Unfortunately, over time any lose soil washes down between the stones, the voids are filled and the soakaway becomes useless.
Water crates, sometimes called modular water storage cells have been constructed to enhance the soakaway system. Water crates are an essential product used in most building projects due to an increasing need for water management. Plastic soakaways, when they are correctly installed are vastly more effective and efficient than their predecessors.
Where do I install the plastic soakaway crates?
Efficient soakaway crates sit within sandy soil. Installing a crate in clay soil isn’t effective as the clay will not allow water to drain through and out of the system.
The ground lower than the level of the building is the ideal place for installation, or at the very least, on the same level. The crates should not be installed any closer than 5m from any building to avoid any compromising of the foundations.
How do I install the soakaway crate?
For a soakaway crate of 1 metre cubed, the hole dug needs to be a depth of 1.6m and 1.2m square. The base should be a 100mm layer of sharp sand, surrounding the crates need to be a 100mm of gravel and a 500mm layer above. You will need to ensure the bottom and sides of the cavity are square and straight.
The soakaway crates are fixed together using small tubes. It’s recommended that you join them together before placing them in the hole.
Non-woven geotextile membrane is used to wrap the outer faces of the crates. This membrane allows permeation of the water at the same time as preventing any thicker consistency, such as soil, from washing through. This ensures that the soakaway is prevented from fragility; without this protection to the membrane, efficiency of the installation is likely to reduce drastically.
The bedrock must be 1 metre completely clear of the bottom of the soakaway drainage pipe. Two metres below ground is usually the ideal placement. The maximum depth to allow for the pipework should be 700mm.
For a 1 cubic metre (5 x 0.2m3) soakaway, you will need 8m x 1m of membrane.
The membrane can be wrapped around the crates once they have been connected together, or alternatively, it is sometimes easier to place the membrane into the pit and the crates can then be lowered on top of it. The membrane needs to be drawn up around the crates sides, ensuring no gaps are left.
Step-by-step process to calculating how many crates I require;
1) Firstly, the roof length needs to be calculated, measure along the eaves.
2) Calculate gable or hip end width.
3) Divide the number by two.
4) Multiply the figure from number step 1 by the figure from number step 3.
5) Ensure you allow for the roof slope by multiplying the roof area by factors shown below, using the roof pitch. (Domestic roofs are usually pitched somewhere between 35 and 45 degrees)