BRE365 Percolation Test
BRE365 PERCOLATION TEST
A BRE365 percolation test establishes whether the ground at a new development site is suitable for infiltration-based forms of Sustainable Drainage Systems (SuDS), such as soakaways. The test measures the soil’s water absorption rate to determine whether ground conditions are appropriate for infiltration.
Where infiltration is feasible, surface water arising from a development can be managed and treated at source. This means it doesn’t have to be conveyed to surface water networks or rivers, reducing the risk of overloading them and causing flooding.
BRE365 infiltration and percolation tests are often required as part of planning applications, or to discharge planning conditions, especially where infiltration forms of SuDS are recommended. SuDS aim to alleviate drainage problems by treating surface water run-off at source, or by attenuating it and releasing it back into the surface water network at a much lower rate.
At Nimbus Engineering, we carry out BRE365 testing in house and incorporate the results directly into your SuDS report and drainage strategy — giving you a single, coordinated point of contact for your project.
WHAT IS A SOAKAWAY?
Soakaways are underground drainage systems designed to store surface water run-off before gradually allowing it to infiltrate into the ground. They are a key component of Sustainable Drainage Systems (SuDS) and sit high in the SuDS hierarchy, as they keep surface water run-off within the site rather than discharging it to local surface water networks, watercourses or rivers — which could otherwise lead to overloading and flooding.
To work effectively, a soakaway must be able to release stored water into the ground relatively quickly, maintaining enough capacity to receive high volumes of run-off during periods of heavy rainfall or storms. Establishing whether the ground is suitable for a soakaway requires a BRE365 percolation test to measure the soil’s infiltration rate.
Soakaways are a sustainable and effective drainage solution for new developments. The infiltration process helps recharge underlying aquifers, requires minimal maintenance, and — when properly designed and installed — can have a lifespan of at least 100 years.
WHY ARE PERCOLATION AND SOAKAWAY TESTS IMPORTANT?
Percolation tests should be carried out during the design stage of development, as part of the ground investigation, before construction commences.
BRE365 percolation tests follow the guidance of the Building Research Establishment (BRE). The process calculates the soil infiltration rate, which allows us to size any proposed soakaway or other infiltration device, based on a 1 in 100-year storm event plus a 40% climate change allowance.
In simple terms, a BRE365 percolation or infiltration test measures how quickly water drains from the soil. Once we’ve established this rate, we can calculate the correct soakaway or infiltration device size, which ultimately informs our final drainage design.
According to BRE365 guidance, a soakaway should discharge from full to half-volume within 24 hours. This ensures the soakaway or infiltration device has enough capacity to cope with a further storm event within that period.
WHY AM I BEING ASKED TO HAVE A BRE365 PERCOLATION TEST CARRIED OUT AT PLANNING APPLICATION STAGE?
Local Planning Authorities (LPAs) and Lead Local Flood Authorities (LLFAs) request SuDS reports at the planning application stage to ensure development proposals have properly considered surface water run-off, and that feasible drainage measures are in place before construction begins. A key reason for this is that SuDS need space — all infiltration devices must be located a minimum of 5 metres from a habitable building.
Most developers naturally want to make the most of the available space on a site, which can leave little room for a soakaway. If the BRE365 percolation test passes but there isn’t sufficient space for a soakaway, the planning authority may ask you to amend the site layout to provide room for infiltration.
For major developments where a desktop geological study shows underlying geology with infiltration potential, the LPA and LLFA will typically request a BRE365 infiltration test on site. This demonstrates that the SuDS hierarchy has been followed. If the test fails, it also allows us to investigate alternative methods of restricted surface water disposal — ensuring SuDS can still be incorporated into the development, and that there is a viable destination for any restricted surface water discharge.
It’s worth noting that sites with high clay content or a high water table are also generally unsuitable for soakaways.
Ultimately, carrying out a BRE365 percolation test demonstrates to your local authority that you’ve taken the necessary steps to establish ground conditions as part of your planning application.
CHOOSE NIMBUS
We provide comprehensive on-site BRE365 percolation tests to accurately determine infiltration rates at your development site — a critical step in assessing the feasibility of soakaways and other infiltration-based sustainable drainage solutions. With our in-house engineers handling the testing process from initial assessment through to final reporting, you get a streamlined, efficient service and a single point of contact.
Where your planning application requires a Sustainable Drainage Systems (SuDS) strategy, and preliminary desktop geological assessments indicate suitable ground conditions, BRE365 testing is essential. It confirms whether infiltration-based drainage such as soakaways is viable, and allows us to design these systems to the correct specifications in line with current standards.
As experienced environmental and drainage consultants, we provide up-to-date, practical advice on surface water management, SuDS design and drainage strategies. Our reports are tailored to meet both national guidance and local planning authority requirements, giving you the best possible chance of securing planning approval without delays.
We also offer early-stage consultancy to help integrate sustainable drainage solutions into your development from the outset. This proactive approach allows potential constraints and risks to be addressed efficiently, while promoting environmentally responsible design. Using industry-recognised methods and calculations, we deliver detailed, cost-effective reports that minimise surface water run-off and support long-term site sustainability.
Get in touch today to discuss your project requirements. Our team specialises in Flood Risk Assessments, surface water management and SuDS design, and we’re here to guide you through the planning process.
Customer Reviews
“I am very happy with the work Nimbus have carried out for me over the last 10 years. They always deliver a good service at a very good price and always high quality reports and fast turn around. They have carried out work on many of my projects in Croydon and I have never had a problem with their work.”
“I have worked with Nimbus Engineering for many years. I can always count on them to deliver comprehensive flood risk assessments, drainage strategy and SuDS reports, on time and at a competitive price. More importantly, I can’t think of a single occasion where a council has not accepted the report’s.”
“I have used Nimbus Engineering for a number of projects over the last 10 years and have always found them to be flexible, highly skilled and great value for money. Anyone looking for Flood Risk and/or Sustainable Urban Drainage System advice need look no further, Nimbus have the solution.”
Get A Quote Today
Get in touch with Nimbus Engineering Consultants for SuDS reports, drainage design, or general engineering enquiries. Our team will be happy to provide advice or a quotation for your project.
