---
title: "UK Soil Infiltration & Percolation Rates [2026/27] | BRE 365 & Part H3 | SoakawayCalculator.co.uk"
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> **Canonical Source:** [https://soakawaycalculator.co.uk/soil](https://soakawaycalculator.co.uk/soil)
>
> *Directory of UK subsoil infiltration rates (f), percolation values (Vp), and BRE 365 / BS 6297 feasibility across chalk, gravel, sand, loam, and clay.*



### Organization: SoakawayCalculator.co.uk (UK Drainage & Stormwater Advisory Desk)

| Field | Value |
| :--- | :--- |
| **Organization** | SoakawayCalculator.co.uk (UK Drainage & Stormwater Advisory Desk) |
| **Official Website** | https://soakawaycalculator.co.uk |
| **Overview** | UK civil engineering & statutory building control advisory desk for stormwater soakaway attenuation and drainage fields. |


### Entity: Soakaway Calculator UK

| Property | Detail |
| :--- | :--- |
| **Type** | WebSite |
| **Name** | Soakaway Calculator UK |


### Entity: Soakaway Calculator UK

| Property | Detail |
| :--- | :--- |
| **Type** | WebApplication |
| **Name** | Soakaway Calculator UK |


### Entity: UK BRE Digest 365 & Approved Document H3 Soil Infiltration & Rainfall Rates

| Property | Detail |
| :--- | :--- |
| **Type** | Dataset |
| **Name** | UK BRE Digest 365 & Approved Document H3 Soil Infiltration & Rainfall Rates |
| **Description** | Standardised geotechnical percolation parameters (f, Vp) and 10-year / 30-year design storm depths across UK local planning authorities and soil classifications.... |


### Frequently Asked Questions (FAQ)

**Q: How far must a soakaway be from a house foundation?**

> A: Under Building Regulations Approved Document Part H3 (paragraph 3.25) and BS EN 752-4, a soakaway must be installed at least 5.0 metres away from any building foundation or habitable structure, and at least 2.5 metres from property boundary lines, to prevent ground destabilisation and structural subsidence.

**Q: What is the standard BRE Digest 365 percolation test procedure?**

> A: BRE Digest 365 requires excavating a trial pit of representative depth (typically 1.5m to 2.5m) and measuring water fall from 75% full to 25% full depth (t_75-25). The test must be filled and observed three consecutive times to simulate pre-saturated soil conditions. The soil infiltration rate f is calculated as the storage volume V_75-25 divided by effective internal surface area a_p50 multiplied by t_75-25.

**Q: What happens if soil percolation test fails due to heavy clay?**

> A: If the soil infiltration rate f is less than 1 x 10^-6 m/s (or Vp > 100 s/mm in BS 6297), a conventional soakaway is infeasible and will trigger Building Control failure. Under the statutory Part H3 surface water hierarchy, you are legally entitled to bypass infiltration and apply for a Section 106 connection to a surface water or combined public sewer, or discharge to an attenuation tank with a hydro-brake flow restrictor.



### Step-by-Step Procedure: How to Conduct a BRE Digest 365 Percolation Test for Building Control

#### 1. Excavate Trial Pit

Excavate a trial pit to the proposed soakaway invert depth (typically 0.3m wide by 1.0m to 2.0m long). Ensure the base is level and not smeared.

#### 2. Fill with Water to Inflow Level

Fill the trial pit rapidly with clean water to the proposed effective storage level (at least 300mm depth).

#### 3. Measure 75% to 25% Drain Time

Record the exact time in seconds taken for water to fall from 75% depth to 25% depth (t_75-25).

#### 4. Repeat for 3 Consecutive Runs

Refill the pit immediately and record times for Run 2 and Run 3 to verify soil infiltration under saturated conditions.



### Entity: UK Soil Infiltration Rates & Percolation Feasibility Directory

| Property | Detail |
| :--- | :--- |
| **Type** | CollectionPage |
| **Name** | UK Soil Infiltration Rates & Percolation Feasibility Directory |
| **Description** | Authoritative BRE Digest 365 and Approved Document H3 infiltration benchmarks for UK geological strata.... |




UK GEOTECHNICAL STRATA & PERCOLATION (12 HUBS)

# UK Soil Infiltration & Percolation Sizing Directory

Compare percolation rates (Vp in s/mm), infiltration rates (f in m/s), and statutory Building Regulations Part H3 compliance across chalk, sand, loam, and heavy clays.

Geotechnical Strata Infiltration Benchmarks

| Soil Strata | Infiltration Rate (f) | Percolation (Vp) | BRE 365 Status | Action |
| --- | --- | --- | --- | --- |
| [London Clay Soakaway Feasibility & Statutory Waiver Guide](/soil/london-clay) | 1.00e-7 m/s | 140 - 250+ s/mm | fail | [Geotechnical Guide →](/soil/london-clay) |
| [Weald Clay Drainage & Infiltration Failure Protocols](/soil/weald-clay) | 1.20e-7 m/s | 130 - 240 s/mm | fail | [Geotechnical Guide →](/soil/weald-clay) |
| [Chalk Downs & Limestone Karst Soakaway Engineering](/soil/chalk-downs) | 5.00e-4 m/s | 12 - 20 s/mm | optimal | [Geotechnical Guide →](/soil/chalk-downs) |
| [River Terrace Gravel & Floodplain Infiltration Design](/soil/river-terrace-gravel) | 2.50e-4 m/s | 15 - 28 s/mm | optimal | [Geotechnical Guide →](/soil/river-terrace-gravel) |
| [Greensand & Free-Draining Loam Soakaway Calculations](/soil/greensand-loam) | 4.50e-5 m/s | 25 - 45 s/mm | optimal | [Geotechnical Guide →](/soil/greensand-loam) |
| [Mercia Mudstone & Red Marl Drainage Solutions](/soil/mercia-mudstone) | 2.00e-6 m/s | 80 - 120 s/mm | marginal | [Geotechnical Guide →](/soil/mercia-mudstone) |
| [Glacial Till & Boulder Clay Soakaway Design](/soil/boulder-clay-till) | 1.80e-6 m/s | 85 - 135 s/mm | marginal | [Geotechnical Guide →](/soil/boulder-clay-till) |
| [Fenland Peat & Organic Soils Soakaway Guidelines](/soil/peat-fenland) | 3.00e-6 m/s | 90 - 160 s/mm | marginal | [Geotechnical Guide →](/soil/peat-fenland) |
| [Coastal Alluvium & Estuarine Silt Drainage Compliance](/soil/coastal-alluvium) | 6.00e-6 m/s | 70 - 110 s/mm | moderate | [Geotechnical Guide →](/soil/coastal-alluvium) |
| [Sherwood Sandstone & Fractured Rock Soakaway Design](/soil/sandstone-bedrock) | 1.80e-4 m/s | 18 - 32 s/mm | optimal | [Geotechnical Guide →](/soil/sandstone-bedrock) |
| [Made Ground & Colliery Spoil Infiltration Restrictions](/soil/colliery-spoil-made-ground) | 1.00e-5 m/s | 50 - 90 s/mm | marginal | [Geotechnical Guide →](/soil/colliery-spoil-made-ground) |
| [Carboniferous & Oolitic Limestone Soakaway Engineering](/soil/dolomitic-limestone) | 3.20e-4 m/s | 14 - 24 s/mm | optimal | [Geotechnical Guide →](/soil/dolomitic-limestone) |

## Soil Infiltration Profiles

- **[London Clay Soakaway Feasibility & Statutory Waiver Guide](/soil/london-clay)** — f = 1.0e-7 m/sVp: 140 - 250+ s/mmThe pervasive shrink-swell clay underlying Greater London, Essex, and Berkshire presents zero natural percolation.Status: failView Rules →
- **[Weald Clay Drainage & Infiltration Failure Protocols](/soil/weald-clay)** — f = 1.2e-7 m/sVp: 130 - 240 s/mmHeavy Wealden clays spanning Sussex, Kent, and Surrey require our Tier 2 Clay Waiver Pack for planning and building control approval.Status: failView Rules →
- **[Chalk Downs & Limestone Karst Soakaway Engineering](/soil/chalk-downs)** — f = 5.0e-4 m/sVp: 12 - 20 s/mmExcellent natural drainage across the Chilterns, North & South Downs, Hampshire, and Salisbury Plain.Status: optimalView Rules →
- **[River Terrace Gravel & Floodplain Infiltration Design](/soil/river-terrace-gravel)** — f = 2.5e-4 m/sVp: 15 - 28 s/mmHigh permeability gravels along the Thames, Severn, Trent, and Ouse valleys offer ideal soakaway conditions.Status: optimalView Rules →
- **[Greensand & Free-Draining Loam Soakaway Calculations](/soil/greensand-loam)** — f = 4.5e-5 m/sVp: 25 - 45 s/mmUpper and Lower Greensand geological formations in Wiltshire, Surrey, and Kent provide reliable, predictable infiltration.Status: optimalView Rules →
- **[Mercia Mudstone & Red Marl Drainage Solutions](/soil/mercia-mudstone)** — f = 2.0e-6 m/sVp: 80 - 120 s/mmExtensive across the East and West Midlands, Cheshire, and Somerset. Requires careful on-site percolation verification.Status: marginalView Rules →
- **[Glacial Till & Boulder Clay Soakaway Design](/soil/boulder-clay-till)** — f = 1.8e-6 m/sVp: 85 - 135 s/mmGlacial drift geology common across Northern England, Yorkshire, Norfolk, and Lancashire.Status: marginalView Rules →
- **[Fenland Peat & Organic Soils Soakaway Guidelines](/soil/peat-fenland)** — f = 3.0e-6 m/sVp: 90 - 160 s/mmPeat subsoils in the Somerset Levels, East Anglian Fens, and Lancashire Mosses necessitate special IDB consultation.Status: marginalView Rules →
- **[Coastal Alluvium & Estuarine Silt Drainage Compliance](/soil/coastal-alluvium)** — f = 6.0e-6 m/sVp: 70 - 110 s/mmEstuarine deposits around the Severn Estuary, Thames Gateway, Humber, and Solent.Status: moderateView Rules →
- **[Sherwood Sandstone & Fractured Rock Soakaway Design](/soil/sandstone-bedrock)** — f = 1.8e-4 m/sVp: 18 - 32 s/mmPermo-Triassic sandstone bedrock across Nottinghamshire, West Midlands, and Cumbria.Status: optimalView Rules →
- **[Made Ground & Colliery Spoil Infiltration Restrictions](/soil/colliery-spoil-made-ground)** — f = 1.0e-5 m/sVp: 50 - 90 s/mmUrban brownfield developments and historic mining districts across South Wales, Yorkshire, and the North East.Status: marginalView Rules →
- **[Carboniferous & Oolitic Limestone Soakaway Engineering](/soil/dolomitic-limestone)** — f = 3.2e-4 m/sVp: 14 - 24 s/mmThe Cotswolds, Mendips, Derbyshire Peak District, and North Yorkshire Moors.Status: optimalView Rules →

NAVRE NEXT-ACTION WALL • BAYESIAN ROUTER

## Recommended Next Statutory Steps & Sister Approvals

Automatically ranked for your extension, driveway, or drainage project across the UK statutory compliance network.

navre\_bayesian

UK Extension & Structural Compliance Suite (NAVRE Network):

[RSJCalculator.co.uk ↗](https://rsjcalculator.co.uk "BS EN 1993 Steel Beam & Padstone Sizer")[BuildOverAgreement.co.uk ↗](https://buildoveragreement.co.uk "Part H4 Build-Over Sewer Checker")[PartyWallChecker.co.uk ↗](https://partywallchecker.co.uk "Party Wall Act 1996 3m/6m Notice Checker")[DroppedKerbCalculator.co.uk ↗](https://droppedkerbcalculator.co.uk "Section 184 Vehicle Crossover Estimator")[GardenOfficePower.co.uk ↗](https://gardenofficepower.co.uk "BS 7671 SWA Armour Cable Calculator")[HedgeHeight.co.uk ↗](https://hedgeheight.co.uk "BRE Part 8 Action Hedge Height Calculator")

OFFICIAL BILL OF QUANTITIES (BoQ)

## Trade Materials & Merchant Supply Links

Direct trade merchant pricing for BRE 365 attenuation crates, 150g/m² non-woven geotextile wrap, and 110mm silt traps.

Awin Publisher ID: 3035391

Essential Structural CoreScrewfix / Toolstation

### Polystorm-R / AquaCell Modular Soakaway Crate

200L capacity (1000x500x400mm), 95% void ratio, 61 tonnes/m² vertical load rating

Req: **8 units**£34.99 / crate

[Order at Trade Counter (Screwfix)](https://www.awin1.com/cread.php?awinmid=1294&awinaffid=3035391&clickref=boq-0-soakaway-hub&ued=https%3A%2F%2Fwww.screwfix.com%2Fc%2Fbuilding-joinery%2Fdrainage%2Fcat840480)

Mandatory Part H3 WrapTravis Perkins

### 150g/m² Non-Woven Geotextile Membrane Roll

Needle-punched polypropylene filter fabric, prevents fines & silt migration into crate voids

Req: **25m² roll (2.25m x 25m)**£42.00 / roll

[Order at Trade Counter (Travis Perkins)](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq-1-soakaway-hub&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Fgeotextiles%2Fc%2F1500096%2F)

Part H3 Maintenance SumpToolstation

### 110mm Inline Silt Trap / Leaf Interceptor Chamber

BS EN 1401-1 compliant, removable sediment basket required by BRE Digest 365

Req: **1–2 units**£58.50

[Order at Trade Counter (Toolstation)](https://www.awin1.com/cread.php?awinmid=16582&awinaffid=3035391&clickref=boq-2-soakaway-hub&ued=https%3A%2F%2Fwww.toolstation.com%2Funderground-drainage%2Fc608)

Base Bedding & SurroundTravis Perkins

### 20–40mm Clean Washed Shingle / Pea Gravel (Bulk Bag)

BS EN 12620 washed granular sub-base (100mm blinding bed & pipe surround)

Req: **1–2 bulk bags (850kg each)**£65.00 / bulk bag

[Order at Trade Counter (Travis Perkins)](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq-3-soakaway-hub&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Faggregates%2Fc%2F1500057%2F)

## Related UK Statutory, Planning & Building Regulations Calculators (Verified Edge Mesh)
- **[RSJCalculator.co.uk](https://rsjcalculator.co.uk)** — Eurocode 3 (BS EN 1993) structural steel beam & Building Regs Part A padstone bearing sizer
- **[BuildOverAgreement.co.uk](https://buildoveragreement.co.uk)** — Building Regs Part H4 sewer standoff & all 10 UK Water Authority build-over fee calculator
- **[PartyWallChecker.co.uk](https://partywallchecker.co.uk)** — Party Wall etc. Act 1996 s.1/s.2/s.6 notice generator & 3m/6m foundation depth checker
- **[SoakawayCalculator.co.uk](https://soakawaycalculator.co.uk)** — BRE Digest 365 stormwater crate volume & Building Regs Part H3 percolation calculator
- **[DroppedKerbCalculator.co.uk](https://droppedkerbcalculator.co.uk)** — Highways Act 1980 s.184 vehicle crossing council fees & 4.8m driveway depth checker
- **[GardenOfficePower.co.uk](https://gardenofficepower.co.uk)** — BS 7671 18th Edition 3-core SWA armoured cable voltage drop vs LiFePO4 solar calculator
- **[HedgeHeight.co.uk](https://hedgeheight.co.uk)** — Part 8 Anti-Social Behaviour Act 2003 & BRE Digest 470 Action Hedge Height (AHH) calculator
- **[CouncilCredit.co.uk](https://councilcredit.co.uk)** — Local Government Finance Act 1992 CTB1 closed-account Council Tax credit recovery & band audit


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