--- title: "Soakaway Calculator Widget | UK Civil Drainage | SoakawayCalculator.co.uk" source_url: "https://soakawaycalculator.co.uk/widget" retrieved_by: "AnswerRail Edge Engine v1.1.0-parity-v20 (https://answerrail.com)" level_of_detail: "standard" token_payload_reduction: "89.1%" raw_html_bytes: 78666 compiled_body_bytes: 8551 entities_extracted: 6 currency_recall_static_html: "38%" monitored_currency_tokens: 8 link_recall_static_html: "100%" monitored_content_links: 5 rfc_compliance: "RFC 9110" last_verified_at: "2026-10-17T12:55:40.086Z" cache_age_seconds: 0 origin_cache_control: "public, max-age=0, must-revalidate" --- > **Canonical Source:** [https://soakawaycalculator.co.uk/widget](https://soakawaycalculator.co.uk/widget) > > *Free 30-second UK Soakaway Calculator [2026/27]. Calculate BRE Digest 365 stormwater crates, 3-run trial pit percolation (f & Vp), BS 6297 septic drainage fields, 5.0m setbacks & clay soil waivers.* ### 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. UK British Geological Survey & Water Undertaker Auto-Detector Instant BGS strata lookup, statutory Water Undertaker mapping, clay failure risk & EA climate surge factor. Quick Test:SW19 (London Clay)RG4 (Chalk)M20 (Boulder Clay)B15 (Midlands Loam) STATUTORY CIVIL CALCULATION ENGINE ## UK Soakaway & Drainage Field Sizing Building Regulations Approved Document Part H (H2/H3) & BRE Digest 365:2016 Compliant Mode A: Rainwater (BRE 365)Mode B: Septic Field (BS 6297) ### 1\. Roof Catchment Area 83.9 m² effective Quick Property Presets (1-Click) Extension (25m²)Double Garage (36m²)3-Bed Semi (65m²)4-Bed Detached (110m²)Barn / Commercial (250m²) Length (m) Width (m) Roof Pitch (°)Flat Roof (0°)Shallow (20°)Standard Pitch (35°)Steep Pitch (45°) Or Direct Area (m²) ### 2\. Ground & Soil Type f = 3.5e-5 m/s Regional Soil Presets (Instant Sizing) Chalk / Gravel (Pass)Sandy Loam (Pass)Silty Clay (Marginal)London / Weald Heavy Clay (Fail) Soil ClassificationChalk & Fractured Gravel (5.0e-4 m/s)Coarse Sand & Sandy Gravel (1.2e-4 m/s)Sandy Loam / Light Loam (3.5e-5 m/s)Silty Loam & Fine Silt (8.0e-6 m/s)Sandy Clay / Clay Loam (1.5e-6 m/s)Heavy London / Oxford / Weald Clay (1.0e-7 m/s) Sandy Loam / Light Loam Balanced agricultural subsoils with mixed sand, silt, and minor clay fraction. Common across Midlands and East Anglia. Have real trial pit data?\+ Use 3-Run Analyser ### 3\. Storm Design & Crate BRE 365 10-Yr / 30-Yr Storm Duration1-Hour Flash Storm2-Hour Standard Storm6-Hour Sustained Storm24-Hour Winter Storm EA Climate Allowance+20% (Low Risk)+40% (Standard EA / SuDS)+45% (Upper Sensitivity) Attenuation MediumPolystorm 200L Crates (1000x500x400mm, 95% void)AquaCell 400L Crates (1000x1000x400mm, 95% void)Traditional 20-40mm Clean Shingle Pit (30% void) ### Deterministic Sizing Results Calculated according to BRE Digest 365 (2016) & Building Regs Part H 🔗 Copy Shareable LinkGet 3 Contractor Quotes Net Storage Required (S) 3.13 m³ 3,130 Litres capacity Inflow I: 3.76m³ | Outflow O: 0.63m³ Attenuation Crate Count 17 Crates 200L Polystorm Units (95% void) Or 16.6 tonnes clean 20-40mm stone (30% void) Minimum Pit Excavation 4.3m (L) × 2.3m (W) Depth: 0.9m | Total Vol: 8.9 m³ Incl. 100mm aggregate bed & geotextile wrap 24-Hr Half-Empty Time (T₅₀) 0.8 hrs ✓ PASS: Drains within 24 hours Mandatory Building Control check for back-to-back storms Civil Engineering CAD Cross-Section & Setback Schematic (Section A-A) Scale: 1:50 Schematic•BRE 365 / BS 6297 / Part H3 **Building Regulations Part H3 para 3.25: 5.0 Metre Foundation Setback**Ensure the soakaway crate pit is positioned at least **5.0 metres away** from any building or retaining wall foundation, and at least **2.5 metres** from site boundary fences. **Party Wall Act 1996 Section 6 (3m / 6m Excavation Notice)**If excavating deeper than an adjoining owner's foundation within 3.0m, or within 6.0m on a 45-degree angle, you must serve a statutory Party Wall Notice 1 month prior to works. ### Bill of Quantities (BoQ) Material Spec & Trade Pricing Direct merchant procurement links with verified trade account pricing. UK Trade Counter Spec Modular Attenuation CratesTravis Perkins Polystorm 200L (95% void ratio, BBA certified for driveways or gardens) 17 units~£595 est. [Check Trade Price↗](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq_crates&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Fproduct%2Fbuilding-materials%2Fcivils-and-drainage%2Fsurface-water-drainage%2Fsoakaway-crates%2Fc%2F1500054%2F) 150g/m² Non-Woven Geotextile MembraneTravis Perkins Full perimeter & top wrap with 300mm overlaps to prevent soil fines migration 28 m²1 Roll (2m × 25m) ~£42 [Check Trade Price↗](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq_geotextile&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Fproduct%2Fgardens-and-landscaping%2Flandscaping-and-demolition%2Fgeotextiles-and-membranes%2Fc%2F1500152%2F) 110mm Silt Trap & Inspection ChamberScrewfix Essential upstream silt filtration bucket with inspection riser (prevents crate clogging) 1 unit~£58 est. [Check Trade Price↗](https://www.awin1.com/cread.php?awinmid=1294&awinaffid=3035391&clickref=boq_silt_trap&ued=https%3A%2F%2Fwww.screwfix.com%2Fc%2Fheating-plumbing%2Funderground-drainage%2Fcat831504) 20-40mm Clean Washed Drainage ShingleTravis Perkins 100mm aggregate bed under crates plus side surround (30% porosity void ratio) 16.6 tonnes~£1079 est. [Check Trade Price↗](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq_shingle&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Fproduct%2Fbuilding-materials%2Faggregates%2Fbagged-aggregates%2Fc%2F1500002%2F) Total Estimated Materials:£1640 – £2077|Turnkey Groundworks Install:£1694 – £3064 Estimates exclude VAT. Actual pricing depends on site access, spoil removal distance, and soil compaction. Get 3 Vetted Groundworker Quotes (Free)[Order Trade Materials Online ↗](https://www.awin1.com/cread.php?awinmid=2024&awinaffid=3035391&clickref=boq_order_all&ued=https%3A%2F%2Fwww.travisperkins.co.uk%2Fproduct%2Fbuilding-materials%2Fcivils-and-drainage%2Fsurface-water-drainage%2Fsoakaway-crates%2Fc%2F1500054%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 --- ## AI Ingestion & Edge Optimization Provenance (AnswerRail Verified) - **Edge Delivery & Markdown Compilation:** [AnswerRail.com](https://answerrail.com) — Layer-7 AI Crawler Content Negotiation, `/llms.txt` & Byte-0 Schema Compiler - **Dedicated AI Markdown Subdomain:** https://ai.soakawaycalculator.co.uk/ - **Cryptographic Ingestion Certificate:** https://answerrail.com/verify/soakawaycalculator.co.uk - **Live Crawler & Referral Telemetry:** https://answerrail.com/stats/soakawaycalculator.co.uk