Drainage Central offer Brett Martin's StormCrate 55 Attenuation Soak Away Crates.

Storm Crate Dimensions: L1200mm x W600mm x D347mm
One crate = 0.25m3
95% Void Ratio

All crates are manufactured from recycled material.

The StormCrate55 is ideal for soakaways, creating a temporary space for water to sit and eventually soak away.

This Storm Crate has a shallow installation depth with only 250mm cover required for driveway loading, meaning less digging and site spoil. It is also a high strength crate with a load bearing of up to 55 tonne when installed correctly.

How do I work out how many soakaway crates I need? (these notes are for general guidance only, it is dependant on the application - there are many different factors to take into account and usually a drainage engineer would do the calculations for an attenuation or infiltration system)

The full list of information preferred is as follows:

• The geographical location of the site
• The storm return period to be used
• Catchment area(s)
• Soil infiltration rate (derived from porosity tests) for soakaways
• Ground water table level
• Allowable outflow rate (for attenuation systems)
• Safety factor to be applied
• Drainage invert levelsIn a scenario for a single dwelling development where the ground is suitable for a soakaway, multiply the roof area by 0.02 to give a volume equal to 20mm of water over the roof (as per BS EN 752 ? 2008). That will give the cubic metres required. Remember, one crate is equal to 0.25m3 (cubed).

Basic Example

Roof Area 283.03m² x 0.02 = 5.67m³

23 crates would give 5.75m³ of capacity
 
This is only for single dwelling developments, and only for soakaways where the soil is suitable for soakaways; ie not clay. You cannot say for attenuation as everything depends on the allowable flowrate into the public sewer.
Storm Crate 55 Brochure.