Free to size. Building Control-ready PDF £25 +VAT (£30 inc VAT).
Runs in your browser. Enter your percolation test, choose the construction, read off the size.
What a crate soakaway is
A crate soakaway is built from modular plastic geocellular units — soakaway crates — stacked in an excavation and wrapped in a geotextile membrane. The crates are almost entirely hollow, with a void ratio around 95%, so they store far more water per cubic metre of excavation than loose stone.
When to use one
Crates are the go-to where space is tight or the storage volume is large — driveways, extensions and new builds where a gravel pit would mean an enormous hole. Because roughly 95% of a crate is usable storage, you dig the smallest excavation for a given design volume.
How it's sized to BRE 365
BRE Digest 365 sizes a soakaway by the storage volume it must hold in the design storm. With crates at around 95% void, the volume of crates you need is close to that raw storage figure — far less than a filled pit. SoakMonkey takes your percolation rate and catchment, runs the storm-duration sweep, and returns the crate volume that passes.
Crates need adequate cover for any traffic above, a silt trap or catchpit to keep fines out, and enough clearance above the water table. Wrap the whole assembly in a non-woven geotextile.
Free to size — pay only for the report
SoakMonkey is free to use: enter your percolation test, add the area draining to the soakaway, and read the size on screen for nothing. You only pay £25 +VAT (£30 inc VAT), once, when you export the Building Control-ready PDF — with the percolation analysis, the BRE Digest 365 storm table and the dimensioned result.
Frequently asked questions
What is a crate soakaway?
A crate soakaway is built from modular plastic geocellular units — soakaway crates — stacked in an excavation and wrapped in a geotextile membrane. The crates are almost entirely hollow, with a void ratio around 95%, so they store far more water per cubic metre of excavation than loose stone. Crates are the go-to where space is tight or the storage volume is large — driveways, extensions and new builds where a gravel pit would mean an enormous hole. Because roughly 95% of a crate is usable storage, you dig the smallest excavation for a given design volume.
How is a crate soakaway sized to BRE Digest 365?
BRE Digest 365 sizes a soakaway by the storage volume it must hold in the design storm. With crates at around 95% void, the volume of crates you need is close to that raw storage figure — far less than a filled pit. SoakMonkey takes your percolation rate and catchment, runs the storm-duration sweep, and returns the crate volume that passes.
Is the crate soakaway calculator free?
Yes — entering your percolation test and sizing the soakaway on screen is free. You only pay £25 +VAT (£30 inc VAT) when you export the Building Control-ready PDF.
Anything to watch on site?
Crates need adequate cover for any traffic above, a silt trap or catchpit to keep fines out, and enough clearance above the water table. Wrap the whole assembly in a non-woven geotextile.
Other soakaway types
SoakMonkey sizes every common construction. Compare another:
Or back to the main soakaway calculator, size one for a house extension, or work out what size you need.