BRE 365 Soakaway Testing: Everything You Need to Know
When dealing with surface water management in new developments, one of the first questions to answer is: can the ground on your site absorb water effectively? This is where BRE 365 soakaway testing comes in. The primary purpose of the BRE 365 Soakaway Test is to evaluate the suitability of soil conditions for soakaway installation, which is essential for effective surface water management. The test helps determine if a natural underground drainage system—like a soakaway—is viable. It’s essential for designing sustainable surface water drainage solutions and managing surface water runoff safely and efficiently.
Introduction to Soakaway Testing
Soakaway testing is a critical process in surface water management, ensuring that a natural underground drainage system can effectively handle surface water runoff. This testing is essential for various stakeholders, including homeowners, developers, and local planning authorities, as it helps determine the suitability of ground conditions for soakaway installation. The BRE 365 standards play a significant role in soakaway testing, providing a framework for assessing soil infiltration rates and designing suitable drainage systems. By understanding the importance of soakaway testing, individuals can appreciate the need for proper testing and design to prevent flooding and ensure effective surface water drainage.
In scenarios where surface water runoff is a concern, BRE 365 soakaway testing is crucial. This testing is often required at the planning application stage, where local planning authorities and lead local flooding authorities assess development proposals to ensure they can manage surface water runoff effectively. The test helps determine the soil infiltration rate, which is vital for designing suitable drainage systems, including soakaways and other infiltration devices. By conducting BRE 365 soakaway testing, developers can demonstrate their commitment to sustainable drainage systems and reduce the risk of flooding.
Gain a foundational understanding of what soakaway testing entails and its importance in drainage systems.Who Needs This Test?
If your project involves changes to how water drains from the site, there’s a good chance you’ll need a soakaway test. This includes:
- Residential extensions or new builds
- Commercial, industrial, or agricultural developments
- Schools, car parks, or any site with hardstanding
- Sites where SuDS reports are requested by the local planning authority
- Any proposal where drainage flows into the ground rather than a sewer
Understanding flood risk is essential for developing Sustainable Urban Drainage Strategies (SuDS) and ensuring the feasibility of drainage solutions like soakaways.
The lead local flooding authority may also require soakaway testing as part of the development proposal process—especially at the design stage.
Identify the stakeholders and scenarios where BRE 365 soakaway testing is essential.What Is BRE 365?
BRE 365 is a method published by the Building Research Establishment. It sets out the correct procedure for testing the soil conditions to measure the water absorption rate—also known as the infiltration rate. This figure determines whether infiltration drainage, like a soakaway or other infiltration device, is suitable for the site.
Testing is typically required when following the SuDS hierarchy, which prioritises infiltration as the first method of managing surface water. The BRE 365 standards provide a framework for assessing soil infiltration rates and designing suitable drainage systems, comparing traditional methods like soakaways with alternative solutions.
Explore the BRE 365 standards and their significance in soakaway testing.Soakaway Design and Installation
Soakaway design and installation are critical components of surface water management. A well-designed soakaway can effectively manage surface water runoff, reducing the risk of flooding and protecting nearby properties. The design process involves assessing the site’s ground conditions, including soil type and infiltration rate, to determine the suitable size and location of the soakaway. The BRE 365 standards provide guidance on soakaway design, taking into account factors such as soil infiltration rates, gravel soils, and clay soils.
During the installation process, it is essential to consider factors such as the trial pit, test hole, and proper testing procedures. The soakaway must be installed correctly, with adequate depth and space to handle significant volumes of surface water runoff. The planning authority may request SuDS reports to ensure that the development proposal includes a suitable drainage system. By following the BRE 365 standards and guidelines, developers can ensure that their soakaway design and installation meet the required standards, reducing the risk of flooding and protecting the environment.
In addition to soakaway design and installation, it is crucial to consider the site layout and available space for the soakaway. The soakaway must be located in an area with suitable ground conditions, taking into account factors such as the water table and soil type. The construction process must also be carefully planned, ensuring that the soakaway is installed correctly and can handle heavy rainfall events. By prioritizing proper soakaway design and installation, developers can reduce the risk of flooding, protect the environment, and ensure compliance with regulatory requirements.
How Does the BRE 365 Soakaway Test Work?
Here’s what’s involved:
- Excavate a trial pit – Usually 1m³ in size, at the depth of the proposed soakaway.
- Fill it with clean water – Quickly, to simulate runoff from a typical storm event.
- Monitor and record – Track how fast the water soaks into the ground.
- Repeat – At least three test cycles are carried out for accuracy.
From this, an infiltration rate is calculated. This helps determine the soakaway’s size and whether the ground conditions are suitable for infiltration drainage. These tests are crucial for determining soil infiltration rates, which are critical for properly designing drainage systems that manage storm water effectively.
What Happens If the Test Passes or Fails?
If the test passes:
- A soakaway or similar natural underground drainage system can be designed.
- The system is more cost-effective, sustainable, and compliant with SuDS.
- Planning submissions are more likely to be approved with minimal conditions.
If the test fails:
- Your site may have clay soils, a high water table, or compacted ground.
- You’ll need to design a system that uses a different method, like controlled outflow to a surface water network or sewer.
- A qualified engineer can recommend a suitable infiltration device or discharge method that meets planning and drainage standards.
In both cases, test results should be included when you request SuDS reports during the planning process.
Common Soakaway Testing Mistakes to AvoidMany drainage issues arise from poor or incomplete testing. Common red flags include:
- Digging the pit in filled or disturbed soil
- Failing to match the depth of the proposed soakaway
- Ignoring seasonal variation in the groundwater level
- Using a pit that’s too small for reliable results
- Not recording the data or water drop correctly
- Attempting the test without experience or a clean water source
All of these risk invalidating your results—and causing problems once construction begins. These steps help establish whether specific site conditions can manage surface water runoff effectively.
BRE 365 Soakaway Test ChecklistBefore testing starts, make sure the necessary steps are in place:
- Site layout and soakaway location confirmed
- Pit excavated to correct size and depth
- Test area is in natural, undisturbed soil conditions
- Clean water source available
- At least three test cycles completed
- Full recorded observations made
- Infiltration rate calculated and added to SuDS reports
FAQs
Q: Is BRE 365 testing mandatory for all sites?
A: No, but if your drainage design includes infiltration or you’re required to provide a SuDS report, it’s strongly recommended—or required—by most local planning authorities and lead local flooding authorities.
Q: What’s the difference between percolation testing and soakaway testing?
A: They’re often used interchangeably, but percolation testing typically applies to foul drainage (like septic systems), while BRE 365 soakaway testing is specifically for surface water systems.
Q: Can I run the test myself?
A: In theory, yes—but in practice, results are often only accepted if the test is carried out by a professional and includes certified calculations.
Q: How long should it take for water to drain?
A: According to BRE 365, the test should show that water soaks away within 24 hours. If it lingers longer, the soil may not be suitable.
Q: Can a soakaway be used in all soil types?
A: No. Soils with low permeability—such as clay soils—won’t allow water to drain effectively, making soakaways unviable.
Final Thoughts
BRE 365 soakaway testing plays a crucial part in designing a successful drainage system. Whether you’re planning a large residential scheme or a small extension, knowing how your site will handle surface water runoff is vital. A soakaway must discharge from full to half-volume within 24 hours to have enough capacity to handle subsequent storm events.
By understanding your soil conditions, taking the necessary steps, and ensuring your system is installed correctly, you improve your project’s chances of meeting planning approval and avoiding future drainage issues. It’s not just about ticking a box—it’s about protecting your development from the long-term risk of flooding or system failure.
Testing early, using the correct method, and working with reliable data gives your project a stronger, more sustainable foundation—before a single brick is laid. If you need professional guidance or assistance with your soakaway design, IBEX Consulting Engineers can help ensure your drainage system meets all the necessary standards and requirements.
