Rainwater Soakaways: Essential Paperwork and Records to Keep

Whether you are building an extension, paving a substantial area, or fixing chronic waterlogging in your garden, managing surface water is a fundamental part of property maintenance. In England and Wales, surface water disposal is governed by Building Regulations Part H (Drainage and Waste Disposal). Under these rules, rainwater should discharge into the ground via infiltration whenever ground conditions allow, rather than being piped straight into public storm sewers or combined drainage networks.

Because a soakaway is buried out of sight, it is easy to forget about once the soil is backfilled and re-turfed. However, future owners, mortgage surveyors, and drainage engineers cannot easily inspect subsurface modular crates or stone pits without digging up the garden. Keeping an accurate, detailed file of the design, calculations, and installation records ensures you can always prove how your surface drainage was constructed and where it sits.

Building Regulations sign-off and the drainage hierarchy

When a soakaway is installed as part of notifiable building work—such as an extension, a new-build dwelling, or a major roof alteration—it falls under the remit of Building Control. Approved Document H sets out a clear drainage hierarchy: infiltration into the ground via a soakaway is the primary choice, followed by discharge to a watercourse, and only as a last resort, connection to a surface water sewer.

If your soakaway forms part of a wider building project, the Building Control final completion certificate covers the drainage system as part of the whole development. Make sure your builder provides written confirmation from the building inspector that the drainage layout was inspected prior to backfilling. If you install a standalone soakaway to cure a garden drainage issue outside of notifiable building works, Building Regulations may not require formal sign-off, but keeping manufacturer specifications and technical design data remains essential for your property records.

Calculations and test results you must retain

A compliant soakaway is not simply a hole in the ground filled with rubble. It requires precise sizing based on soil porosity and the catchment area it serves. When drainage engineers or groundworkers construct a soakaway, they should generate specific technical documents that you must store safely:

• Percolation test results: Standard soil infiltration tests carried out to BRE Digest 365 or BS 6297 standards, recording how quickly water drains away over consecutive test runs.
• Sizing calculations: Design sheets showing the impermeable catchment area (in square metres), rainfall return period allowances, and the required storage volume in cubic metres.
• Manufacturer technical sheets: Specifications for the attenuation crates or cellular units used, including load-bearing ratings (for example, whether the crates can withstand pedestrian traffic or vehicular loading).
• Geotextile membrane details: Confirmation of the non-woven geotextile membrane specification used to wrap the structure to prevent silt ingress.
• Invoices and delivery notes: Proof of materials purchased, confirming high-density polyethylene crates, pre-formed silt traps, and suitable drainage pipework were installed.

Drainage layouts, depth markers, and photographic proof

One of the most common issues homeowners face years after a soakaway installation is locating the structure. Approved Document H states that a soakaway should typically be sited at least 5 metres away from any building foundation and at least 2.5 metres away from boundary lines. It must also be located at a safe distance from other buried utilities, trees, and neighbouring drainage fields.

Ask your installer for a scale 'as-built' drawing or clear sketch that ties the soakaway's location to fixed reference points on your home, such as building corners or boundary walls. Note the invert levels (the depth of the incoming pipe) and the overall depth of the excavation. In addition, take clear photographs before backfilling: show the excavated pit, the geotextile lining, the assembled modular crates, and the pipework connections running from the rainwater downpipes or silt traps.

Catchpit and maintenance records

Modern soakaways depend on silt management to prevent the void spaces inside the crates from clogging over time. A properly designed installation includes a catchpit, leaf filter, or silt trap upstream of the soakaway. Homeowners should retain the operational manuals for these components and keep a brief log of periodic maintenance—such as clearing out the silt bucket annually and checking downpipe filters.

When you eventually come to sell your home, the Law Society's standard property information forms ask detailed questions about drainage arrangements. Having immediate access to percolation test results, dimensioned layout plans, and photos will allow you to answer buyers' solicitors clearly and avoid unnecessary enquiries. Using an independent record-keeping platform like Project Passport allows you to upload these drainage diagrams, test certificates, and progress photographs into a secure digital record alongside your other property documentation.

By keeping a complete file on your rainwater soakaway from day one, you protect the investment you have made below ground and ensure anyone working on your garden or foundations in the future knows exactly what is beneath their feet.