How to Install a Soakaway Crate: The Comprehensive Guide

If you’ve been searching for ways to prevent waterlogging or flooding around your home or project site, you’ve likely come across soakaway crates. Once upon a time, traditional soakaways consisted of large pits filled with hardcore, stones, and gravel – but these eventually clogged with soil and lost effectiveness.

Today, modular plastic soakaway crates have taken over because they’re not only more efficient, they’re also incredibly durable and versatile. In this comprehensive guide, we’ll walk you through everything you need to know about how to install a soakaway crate, from choosing the right location to backfilling and finishing touches.

How to Install a Soakaway Crate: Understanding What They Are

Soakaway crates (sometimes referred to as modular stormwater cells) are plastic structures used to collect and disperse excess surface water into the surrounding soil. Traditionally, soakaways were constructed using large pits filled with hardcore, stones, and gravel, but these large pits often became ineffective over time as soil particles clogged the voids. Modern systems now use modular water storage cells, also known as soakaway crates, which are more efficient and easier to install because they:

• Provide significantly more storage capacity for water (up to 95-97% void space).
• Are wrapped in non woven membrane to keep silt and soil out, prolonging the system’s life.
• Can be engineered to withstand loads from pedestrians, cars, or even heavier vehicles, depending on the crate specification.

Whether you’re looking to manage roof runoff, driveway water, or general surface drainage, a soakaway crate is a modern, efficient solution.

Why Install a Soakaway Crate?

1. Flood Prevention
   By capturing and slowly releasing water into the surrounding ground, a soakaway prevents sudden surges in surface runoff and helps reduce flood risk.
2. Compliance with Regulations
   Increasingly, local authorities require effective water management systems – especially for new builds or extensions. A soakaway often satisfies these requirements if installed and designed correctly.
3. Eco-Friendly Water Management
   Soakaways help maintain natural groundwater levels by returning water to the soil, rather than overloading sewers or water treatment facilities.
4. Space and Cost Efficiency
   Modern crates can be stacked or laid out in rows, allowing you to adapt to various site conditions and save on excavation costs.

Soakaway crates are also widely used in large commercial developments to manage stormwater on a bigger scale.

What Soakaway Crate Kit is Best For You?

We have multiple choices of soakaway crate kit for different scenarios, depending on the rainfall, area coverage, and load rating. There are 2 different soakaway crates available from EasyMerchant, the Naylor Aquavoid 20 Ton Crates, and the Polystorm 60 Ton Soakaway Crates. The Naylor crates are suitable for domestic projects such as garden drainage, and the Polystorms are necessary for industrial projects such as a public car park.

Each soakaway crate kit comes with a cut of geotextile membrane, waterproof tape, crate clips & shear connectors.

Common Applications of Soakaway Crates

Soakaway crates are a highly adaptable solution for managing excess water in a variety of environments. In residential settings, they’re commonly installed beneath driveways, patios, and gardens to handle stormwater runoff and prevent waterlogging. For commercial and industrial projects, soakaway crates are ideal for use under car parks and pedestrian walkways, where effective drainage is essential to avoid surface flooding and maintain safety.

These systems are also frequently integrated into landscaping projects, helping to create sustainable drainage systems that support healthy plant growth and protect property foundations. Soakaway crates work exceptionally well alongside other water management components, such as galvanised steel gutter and ogee cast iron gutter systems, to direct rainwater efficiently from roofs and hard surfaces into the drainage system.

In areas with clay soil, it’s especially important to use soakaway crates wrapped in a geotextile membrane. This prevents soil particles from entering the system and ensures long-term performance. Whether you’re managing water in a small garden or a large car park, soakaway crates offer a reliable, scalable solution for modern water management challenges.

Building Regulations and Planning Considerations

When installing soakaway crates, it’s crucial to ensure your project complies with all relevant building regulations and planning requirements. In the UK, building regulations specify that soakaway systems must be designed and installed to protect both buildings and the surrounding environment from water damage. Local authorities may have additional requirements, such as minimum cover depths above the crates, specific pipe sizes, and approved materials for use in your soakaway system.

Before installing a soakaway, it’s wise to consult with a civil engineering consultancy to confirm that your design meets all necessary standards. This is especially important for larger construction projects or when integrating soakaway crates with other building elements like soffits replacement fascia, accessories metal fascia, or replacement fascia. Obtaining the appropriate planning permissions is also essential, particularly if your soakaway system is part of a new build or significant extension.

By following these guidelines and working closely with local authorities, you can ensure that your soakaway system is both effective and fully compliant, providing long-term protection for your property.

Environmental Impact of Soakaway Crates

Soakaway crates can play a significant role in promoting sustainable water management and protecting the environment. By allowing rainwater to gradually infiltrate sandy or loamy soil, these systems help reduce stormwater runoff, which in turn minimises the risk of flooding and prevents pollutants from entering local waterways. This process also supports the natural recharge of groundwater aquifers, contributing to a healthier ecosystem.

When used alongside other sustainable drainage solutions – such as permeable paving or green roofs – soakaway crates form part of a comprehensive approach to managing rainwater responsibly. However, to maintain their effectiveness and avoid potential issues like soil contamination or system blockage, regular maintenance is essential. This includes checking and cleaning the silt trap, inspecting the geotextile membrane for signs of clogging by soil particles, and ensuring the minimum cover depth (typically at least 150mm) is maintained according to local regulations.

By choosing soakaway crates and keeping up with routine care, you can enjoy the environmental benefits of efficient drainage while ensuring your system remains reliable for years to come.

Step 1: Confirm Suitability with a Percolation Test

This blog post guide will help you understand how to install a soakaway crate, starting with checking the soil’s ability to drain water. Typically, loamy or sandy soil is ideal. Soakaway crates work best in loamy or sandy soil, as these types facilitate proper water drainage – sandy soil is particularly effective for drainage. If your ground is predominantly clay, it won’t allow water to pass through efficiently – making the soakaway ineffective.

A percolation test involves:

• Digging test pits at the depth you plan to install the soakaway.
• Filling these pits with water and timing how quickly it drains.
• Repeating the process a few times to confirm consistent results.

If the water fails to drain at a reasonable rate, you may need an alternative drainage solution.

Step 2: Determine the Location

• Distance from Buildings
  Position the soakaway at least 5 metres away from any house or structure. This minimum clearance helps protect building foundations by preventing water movement from damaging or undermining them.
• Slope
  Ideally, install the soakaway on land that’s at the same level or lower than your property, ensuring proper water flow and effective drainage away from the building.
• Underground Services
  Avoid gas, water, telecoms, or electrical lines. Always check site plans if you’re unsure.
• Space for Excavation
  Plan for enough space not just for the crate but also for the surrounding backfill of sand or pea shingle (usually around 150mm on all sides).

Step 3: Size Your Soakaway Correctly

The size of your soakaway crate system depends on:

1. Catchment Area: Roof size, driveway, or general surface area draining into it.
2. Rainfall Intensity: Check local maximum rainfall levels if you want to be extra certain.
3. Soil Permeability: Faster-draining soil can handle smaller soakaways.
4. Local Regulations: If the soakaway is part of a new build or extension, have your plans checked by your local authority or a qualified engineer.

A good rule of thumb (though not a substitute for professional calculations):

• 1 cubic metre of soakaway crate often manages around 50m² of roof area.

Crates come in different load-bearing capacities:

• 20-tonne vertical load crates for gardens (pedestrian/light foot traffic).
• 60-tonne vertical load crates for driveways or heavier traffic (cars, 9-tonne vehicles, etc.).

Step 4: Add a Silt Trap (Pre-Filter) for Longevity

Even though the crates are wrapped in geotextile membrane, silt and debris can still enter via the inlet pipe, especially from gutters carrying leaves or dirt. Silt traps (or pre-filters) capture solids before they reach the crates. We strongly recommend installing one if you want to prolong the life of your soakaway. Many silt traps feature a removable bucket, making it easy to remove the captured debris and rinse it out for simple cleaning and maintenance.

Step 5: Excavation

1. Mark Out the Soakaway Pit
   Measure the footprint of your planned soakaway pit plus a minimum of 150mm on each side for backfill. Also account for the vertical depth:

• 150mm base layer (sharp sand or pea gravel).
• Height of your crates (varies by brand).
• Top cover requirements (minimum 150mm soil layer for gardens, increasing up to 1m for heavier traffic).

1. Dig the Soakaway Pit Carefully
   If you’re installing in a lawn, cut and roll turf in strips so you can reuse it. If it’s a large excavation, consider hiring a mini-digger. For deeper or bigger installations, always follow Health and Safety Executive (HSE) guidelines to avoid trench collapse.
2. Check the Base
   Clear out any roots, rubble, or large stones. The bottom should be flat and level. Ensure you will maintain a consistent soil layer above the crates for stability and proper function.

Step 6: Prepare the Base

1. Lay a 150mm Layer of Sharp Sand Spread a 150mm layer of sharp sand at the bottom of the pit. This layer of sharp sand stabilises your crates and aids water percolation.
2. Level the Surface Compact and level the sharp sand to create a uniform bed for the crate assembly.

Step 7: Assemble and Wrap the Crates

1. Connect the Crates
   Assemble the modular soakaway by connecting the modular water storage cells. Most systems either lock together or use cable ties/clips to hold crates in position. Note that these ties only keep crates in place during installation; they’re not structural supports.
2. Wrap in Geotextile Membrane

• Place the membrane across the pit so it drapes evenly on all sides.
• Lower the crates onto the membrane; the weight will help press it into place.
• Carefully pull the membrane up around the sides and overlap it on top (or wrap each crate separately before placing).
• Seal all membrane seams with waterproof tape to prevent soil ingress and enhance durability. Secure any overlaps with tape or clamps to prevent gaps. This membrane prevents soil particles from entering and clogging the soakaway void.

Step 8: Connect the Soakaway to Your Drainage System

1. Stormwater Pipe Entry

• Locate the entry point for the stormwater pipe at the designated pipe entry points or pre formed knockout sections on the crate. Gently cut out or knock through these sections as required.
• If there’s no specific inlet point, you can butt the pipe against the crate and support it with backfill.
• Ensure the inlet pipe is immediately supported after installation to prevent movement or damage during backfilling.

1. Seal Around the Pipe

• Make a small cross-shaped incision in the membrane where the pipe will enter.
• Insert the pipe and tape or clamp the membrane snugly around it to block soil ingress, paying special attention to sealing around all pipe entry points.
• Consider a small layer of ready-mix concrete around the pipe-to-crate junction for extra stability if needed.

1. Install a Silt Trap if Using One

• Position it upstream on the stormwater pipe so it’s easily accessible for maintenance.

Step 9: Backfill and Cover

Side and Back Fill

• Use side filling materials such as sharp sand, gravel, or shingle for side and back fill around the wrapped crates.
• Ensure at least six inches (150mm) of back fill material is placed on all sides of the crates for stability and effective drainage.
• Compact gently to provide stable support, ensuring the crates stay firmly in place and to help minimise ground settlement.

Top Fill

• Spread a 150mm layer of sand or gravel over the top of the crates.
• Follow up with either your excavated soil or suitable backfill material:
• Garden/Lawn: Minimum 150mm of compacted soil is typically enough to achieve a level ground surface.
• Light Traffic: Increase top cover to around 350mm over the initial 150mm of sand/gravel.
• Heavier Loads: If you expect vehicles up to 9 tonnes, a 1m cover depth is often recommended. For HGVs or anything heavier, consult with a structural engineer for exact specifications.
• Compact the soil thoroughly to reduce ground settlement and ensure optimal functionality of the soakaway system.

Replace Turf or Finish Ground Surface

• If you remove turf, roll it back on and water well to help it root.
• For driveways, add the appropriate sub-base (MOT Type 1 or similar) and your final surface (tarmac, paving, etc.).
• Ensure the finished ground surface is level for proper water runoff and long-term performance.

Step 10: Ongoing Maintenance

• Check Gutters and Downpipes: Clear out leaves and debris seasonally to reduce silt build-up.
• Inspect Silt Traps: If installed, empty the trap bucket or mesh regularly.
• Watch for Settling: If depressions appear, simply top them up with soil or fill material.

With proper installation and minimal upkeep, a modern soakaway crate system can last for many years, efficiently diverting excess surface water away from your property and reducing the risk of flooding.

Key Takeaways

• Location Matters: Ensure the soil is permeable (sandy or loamy) and keep the soakaway at least 5 metres from buildings.
• Size Appropriately: While 1m³ per 50m² roof area is a decent rule of thumb, professional calculations or advice may be necessary for larger or complex projects.
• Use a Pre-Filter: A silt trap can dramatically extend the lifespan of your system.
• Wrapping Is Crucial: Non-woven geotextile membrane keeps out silt, ensuring your soakaway remains efficient.
• Follow Load Requirements: Garden crates (around 24-tonne rating) differ from those designed for driveways and heavier loads (65-tonne rating and beyond).

Ready to Get Started?

At EasyMerchant, we offer a wide range of soakaway crates and accessories – everything from geotextile membranes to silt traps – making it simple to put together a reliable and effective drainage solution. If you have any questions about sizing, load-bearing capacities, or choosing the right soakaway system for your project, our knowledgeable team is here to help.

Get in touch with us today for advice, quotes, or to place an order. By following the steps in this guide, you’ll be well on your way to a durable and efficient soakaway system that protects your property and manages rainwater effectively.