--- title: "BRE Digest 365 & Building Regs Part H Soakaway Guides [2026/27] | SoakawayCalculator.co.uk" source_url: "https://soakawaycalculator.co.uk/guides" retrieved_by: "AnswerRail Edge Engine v1.1.0-parity-v20 (https://answerrail.com)" level_of_detail: "standard" token_payload_reduction: "87.8%" raw_html_bytes: 125860 compiled_body_bytes: 15314 entities_extracted: 7 currency_recall_static_html: "100%" monitored_currency_tokens: 4 faq_answer_recall_static_html: "50%" monitored_faq_answers: 2 link_recall_static_html: "100%" monitored_content_links: 24 rfc_compliance: "RFC 9110" last_verified_at: "2026-10-17T12:55:49.476Z" cache_age_seconds: 0 origin_cache_control: "public, max-age=0, must-revalidate" --- > **Canonical Source:** [https://soakawaycalculator.co.uk/guides](https://soakawaycalculator.co.uk/guides) > > *Engineering guides for trial pit percolation testing, modular crate sizing, 5m setback compliance, silt management, and clay soil waiver applications.* ### 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: Statutory Soakaway Engineering & Groundwork Guides | Property | Detail | | :--- | :--- | | **Type** | CollectionPage | | **Name** | Statutory Soakaway Engineering & Groundwork Guides | | **Description** | Authoritative statutory guidance for BRE 365 calculations, Part H compliance, percolation testing, and drainage fields.... | STATUTORY CIVIL & GEOTECHNICAL GUIDES (14 HUBS) # BRE Digest 365 & Building Regulations Part H Technical Guides Comprehensive field manuals for civil engineers, groundwork contractors, architects, and property owners navigating UK surface water drainage compliance. Technical Guides & Statutory Standards Master Index | Guide Title | Category | Statutory Standard | Read Time | Action | | --- | --- | --- | --- | --- | | [BRE Digest 365 (2016) Soakaway Calculation Methodology](/guides/bre-digest-365-calculation-method) | Statutory Standards | BRE Digest 365 (2016 Edition) / CIRIA C753 | 9 min read | [Read Guide →](/guides/bre-digest-365-calculation-method) | | [Approved Document H3: Rainwater Drainage Hierarchy & Rules](/guides/building-regulations-approved-document-h3) | Statutory Standards | Building Regulations 2010 Schedule 1 Requirement H3 | 8 min read | [Read Guide →](/guides/building-regulations-approved-document-h3) | | [Percolation Test Step-by-Step Field Guide (BS 6297 & BRE 365)](/guides/percolation-test-step-by-step-guide) | Testing & Fieldwork | BS 6297:2007+A1:2008 Annex D / BRE Digest 365 Section 2 | 11 min read | [Read Guide →](/guides/percolation-test-step-by-step-guide) | | [BS 6297:2007+A1:2008 Drainage Field Sizing for Off-Mains Sewage](/guides/bs-6297-drainage-field-sizing) | Statutory Standards | BS 6297:2007+A1:2008 & Environment Agency GBR | 10 min read | [Read Guide →](/guides/bs-6297-drainage-field-sizing) | | [The 5-Metre Soakaway Foundation Distance Rule: Engineering & Law](/guides/soakaway-5m-building-distance-rule) | Statutory Standards | Approved Document H3 Paragraph 3.25 / NHBC Standards Chapter 5.3 | 7 min read | [Read Guide →](/guides/soakaway-5m-building-distance-rule) | | [Party Wall Act Section 6: Soakaway Excavations Within 3 Metres](/guides/party-wall-act-3m-excavation-notice) | Statutory Standards | Party Wall etc. Act 1996 Section 6 (Excavation within 3m or 6m) | 8 min read | [Read Guide →](/guides/party-wall-act-3m-excavation-notice) | | [Modular Attenuation Crates vs Traditional Gravel Pit Soakaways](/guides/soakaway-crates-vs-gravel-pit) | Design & Sizing | CIRIA Report 156 / CIRIA C753 | 9 min read | [Read Guide →](/guides/soakaway-crates-vs-gravel-pit) | | [Soakaway Alternatives for Heavy Clay Soils (London, Oxford & Weald)](/guides/heavy-clay-soil-soakaway-alternatives) | Design & Sizing | Approved Document H3 Section 3 / Water Industry Act 1991 s.106 | 10 min read | [Read Guide →](/guides/heavy-clay-soil-soakaway-alternatives) | | [How to Obtain a Water Authority Surface Water Sewer Connection Waiver](/guides/water-company-sewer-connection-waiver) | Statutory Standards | Water Industry Act 1991 Section 106 & Building Regulations Part H3 | 8 min read | [Read Guide →](/guides/water-company-sewer-connection-waiver) | | [Silt Trap Design, Installation & Catch-Pit Maintenance](/guides/silt-trap-installation-maintenance) | Groundwork & Civils | CIRIA C753 SuDS Manual Chapter 13 | 7 min read | [Read Guide →](/guides/silt-trap-installation-maintenance) | | [Permeable Paving & Sub-Base Attenuation (Type 3 Open Graded Stone)](/guides/permeable-paving-sub-base-attenuation) | Design & Sizing | BS 7533-13:2009 & Town and Country Planning Order 2008 | 9 min read | [Read Guide →](/guides/permeable-paving-sub-base-attenuation) | | [High Groundwater Table Soakaway Engineering & Minimum Clearances](/guides/high-groundwater-table-soakaways) | Design & Sizing | BRE Digest 365 Section 1.2 / CIRIA C753 Chapter 13 | 8 min read | [Read Guide →](/guides/high-groundwater-table-soakaways) | | [Non-Woven Geotextile Membrane Specification for Soakaway Wrapping](/guides/non-woven-geotextile-membrane-specification) | Groundwork & Civils | BS EN ISO 10319 / BS EN ISO 11058 / CIRIA C753 | 7 min read | [Read Guide →](/guides/non-woven-geotextile-membrane-specification) | | [Building Control Sign-Off: Drainage Dossier Submission Checklist](/guides/building-control-sign-off-drainage-dossier) | Statutory Standards | Building Regulations 2010 Part H / Manual to the Building Regulations | 9 min read | [Read Guide →](/guides/building-control-sign-off-drainage-dossier) | ## Featured Technical Guides - **[BRE Digest 365 (2016) Soakaway Calculation Methodology](/guides/bre-digest-365-calculation-method)** — Statutory Standards9 min readThe authoritative engineering guide to sizing modular crate and gravel soakaways under UK Building Regulations Approved Document H3.BRE Digest 365 (2016 Edition) / CIRIA C753Read → - **[Approved Document H3: Rainwater Drainage Hierarchy & Rules](/guides/building-regulations-approved-document-h3)** — Statutory Standards8 min readUnderstanding the statutory hierarchy of discharge: ground infiltration first, watercourses second, and public sewer strictly as a last resort.Building Regulations 2010 Schedule 1 Requirement H3Read → - **[Percolation Test Step-by-Step Field Guide (BS 6297 & BRE 365)](/guides/percolation-test-step-by-step-guide)** — Testing & Fieldwork11 min readPractical field methodology for digging trial pits, pre-soaking subsoils, measuring Vp drop rates, and recording photographic evidence.BS 6297:2007+A1:2008 Annex D / BRE Digest 365 Section 2Read → - **[BS 6297:2007+A1:2008 Drainage Field Sizing for Off-Mains Sewage](/guides/bs-6297-drainage-field-sizing)** — Statutory Standards10 min readEngineering wastewater infiltration fields for septic tanks and package sewage treatment plants under UK General Binding Rules.BS 6297:2007+A1:2008 & Environment Agency GBRRead → - **[The 5-Metre Soakaway Foundation Distance Rule: Engineering & Law](/guides/soakaway-5m-building-distance-rule)** — Statutory Standards7 min readWhy Approved Document H3 requires 5 metres from habitable buildings, exceptions for outbuildings, and remedial underpinning.Approved Document H3 Paragraph 3.25 / NHBC Standards Chapter 5.3Read → - **[Party Wall Act Section 6: Soakaway Excavations Within 3 Metres](/guides/party-wall-act-3m-excavation-notice)** — Statutory Standards8 min readHow digging soakaway pits near boundary lines triggers statutory Party Wall notices under Section 6 of the 1996 Act.Party Wall etc. Act 1996 Section 6 (Excavation within 3m or 6m)Read → - **[Modular Attenuation Crates vs Traditional Gravel Pit Soakaways](/guides/soakaway-crates-vs-gravel-pit)** — Design & Sizing9 min readComprehensive engineering comparison: void ratios (95% vs 30%), excavation volumes, skip hire costs, and lifespan.CIRIA Report 156 / CIRIA C753Read → - **[Soakaway Alternatives for Heavy Clay Soils (London, Oxford & Weald)](/guides/heavy-clay-soil-soakaway-alternatives)** — Design & Sizing10 min readWhat to do when percolation fails: attenuation storage tanks with hydro-brake throttles, swales, and public sewer connections.Approved Document H3 Section 3 / Water Industry Act 1991 s.106Read → - **[How to Obtain a Water Authority Surface Water Sewer Connection Waiver](/guides/water-company-sewer-connection-waiver)** — Statutory Standards8 min readStep-by-step procedure for applying under Section 106 of the Water Industry Act 1991 following a percolation test failure.Water Industry Act 1991 Section 106 & Building Regulations Part H3Read → - **[Silt Trap Design, Installation & Catch-Pit Maintenance](/guides/silt-trap-installation-maintenance)** — Groundwork & Civils7 min readPreventing premature soakaway failure: inline filter buckets, leaves, grit, roof moss removal, and jetting access.CIRIA C753 SuDS Manual Chapter 13Read → - **[Permeable Paving & Sub-Base Attenuation (Type 3 Open Graded Stone)](/guides/permeable-paving-sub-base-attenuation)** — Design & Sizing9 min readDesign specifications for porous driveways, MOT Type 3 aggregates, and dual-purpose sub-base stormwater attenuation.BS 7533-13:2009 & Town and Country Planning Order 2008Read → - **[High Groundwater Table Soakaway Engineering & Minimum Clearances](/guides/high-groundwater-table-soakaways)** — Design & Sizing8 min readManaging seasonal water table rebound: the statutory 1.0m unsaturated zone clearance and shallow attenuation solutions.BRE Digest 365 Section 1.2 / CIRIA C753 Chapter 13Read → - **[Non-Woven Geotextile Membrane Specification for Soakaway Wrapping](/guides/non-woven-geotextile-membrane-specification)** — Groundwork & Civils7 min readWhy non-woven needle-punched geotextile (100gsm) is required: pore opening size, water permeability, and woven fabric risks.BS EN ISO 10319 / BS EN ISO 11058 / CIRIA C753Read → - **[Building Control Sign-Off: Drainage Dossier Submission Checklist](/guides/building-control-sign-off-drainage-dossier)** — Statutory Standards9 min readThe exact technical documentation package needed for local authority Building Control and private approved inspectors.Building Regulations 2010 Part H / Manual to the Building RegulationsRead → 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 --- ## 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