--- title: "Soakaway vs Section 106 Sewer Connection (Part H3) | SoakawayCalculator.co.uk" source_url: "https://soakawaycalculator.co.uk/comparisons/soakaway-vs-section-106-sewer-connection" retrieved_by: "AnswerRail Edge Engine v1.2.7-v27 (https://answerrail.com)" level_of_detail: "standard" token_payload_reduction: "90.3%" raw_html_bytes: 85820 compiled_body_bytes: 8288 entities_extracted: 8 currency_recall_static_html: "100%" monitored_currency_tokens: 6 faq_answer_recall_static_html: "100%" monitored_faq_answers: 3 link_recall_static_html: "100%" monitored_content_links: 6 rfc_compliance: "RFC 9110" last_verified_at: "2026-11-07T17:47:49.596Z" cache_age_seconds: 0 origin_cache_control: "public, max-age=0, must-revalidate" --- > **Canonical Source:** [https://soakawaycalculator.co.uk/comparisons/soakaway-vs-section-106-sewer-connection](https://soakawaycalculator.co.uk/comparisons/soakaway-vs-section-106-sewer-connection) > > *Learn when you can bypass Part H3 soakaway rules and legally connect surface water to a public sewer via Water Industry Act 1991 Section 106 after clay failure.* ### 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. ### Frequently Asked Questions (FAQ) **Q: Can a water company refuse a Section 106 surface water connection?** > A: Under Section 106 of the Water Industry Act 1991, undertakers cannot refuse connection provided you prove soakaways and watercourses are unviable under Approved Document H3. **Q: How many percolation test cycles are required to prove clay failure?** > A: BRE Digest 365 requires three consecutive trial pit fill-and-drain tests. If the water fails to drop to 25% depth within 24 hours, the subsoil is certified impermeable. **Q: Is attenuation required before discharging into a public sewer?** > A: Yes. Most water undertakers require throttled discharge (typically 2.0 litres per second) via an on-site attenuation crate tank and flow limiter chamber. Part H3 Hierarchy & WIA 1991 s.106 # Soakaway vs Section 106 Sewer Connection: Clay Soil Exemption Building Regulations Approved Document H3 enforces a statutory drainage hierarchy: infiltration soakaways must be used unless certified impossible. When heavy clay fails the BRE 365 3-cycle percolation test, developers unlock a statutory Section 106 right to connect to the public surface water sewer. Benchmark Focus**Part H3 Hierarchy & WIA 1991 s.106** Primary Standard**BRE 365 / Part H** Option A**Part H3 Infiltration Soakaway (Priority 1)** Option B**Section 106 Public Sewer Connection (Priority 3)** FIG H3-01Statutory Rainwater Discharge Hierarchy Part H3 Para 3.2 Building Control inspectors legally reject public sewer connections unless Priority 1 ground infiltration is proven unfeasible via BRE 365 trial pit records. FIG BRE-02BRE Digest 365 Trial Pit Percolation Geometry Clause 3.1 (3 Runs) BRE Digest 365 excludes the pit floor from outflow area (a₅₀ = 2 × (L + W) × d/2) because fine roof sediment seals horizontal bases over time. ## Head-to-Head Specification Matrix | Evaluation Criterion | Part H3 Infiltration Soakaway (Priority 1) | Section 106 Public Sewer Connection (Priority 3) | Statutory Verdict | | --- | --- | --- | --- | | Part H3 Hierarchy Position | Priority 1: Mandatory on all developments if ground allows | Priority 3: Only permitted once infiltration & watercourse options are ruled out | Hierarchy strictly enforced by LABC | | Soil Permeability Requisite | Requires soil infiltration rate f \>\= 1.0 x 10^-6 m/s | Statutory right invoked when heavy clay fails (f < 1.0 x 10^-6 m/s) | Section 106 protects clay soil sites | | Initial Capital & Installation Cost | £800 – £2,500 total (crates, membrane, aggregate & pipework) | £1,800 – £6,500+ (undertaker application fees, road opening & reinstatement) | Soakaway is significantly lower cost | | Ongoing Water Undertaker Sewerage Charges | £0 / year (eligible for full Surface Water Drainage standing charge exemption) | Annual recurring surface water sewerage charges on water utility bills | Soakaway eliminates utility levies | | Building Control Evidential Requirement | Standard trial pit test calculations and crate sizing sheet | Certified 3-Run Infeasibility Dossier proving ground impermeability | S106 requires formal failure documentation | **Building Control Rejection Alert & Common Failure Trap** Water undertakers (Thames Water, Severn Trent, United Utilities, etc.) automatically refuse Section 106 surface water connection notices unless accompanied by certified BRE 365 3-cycle trial pit logs proving infiltration failure. [Download Part H3 Clay Infeasibility Dossier (£49)](/calculation-pack)[All Statutory Comparisons](/comparisons) ## Frequently Asked Legal & Technical Questions Can a water company refuse a Section 106 surface water connection?▼ Under Section 106 of the Water Industry Act 1991, undertakers cannot refuse connection provided you prove soakaways and watercourses are unviable under Approved Document H3. How many percolation test cycles are required to prove clay failure?▼ BRE Digest 365 requires three consecutive trial pit fill-and-drain tests. If the water fails to drop to 25% depth within 24 hours, the subsoil is certified impermeable. Is attenuation required before discharging into a public sewer?▼ Yes. Most water undertakers require throttled discharge (typically 2.0 litres per second) via an on-site attenuation crate tank and flow limiter chamber. ### Related Statutory Comparisons [All Comparisons →](/comparisons) - [Soakaway Crates vs Gravel Trench: 95% Void vs 30% Aggregate Pit](/comparisons/soakaway-crates-vs-gravel-trench)BRE 365 Hydraulic Efficiency - [BRE Digest 365 vs BS 6297 Drainage Field: Stormwater vs Foul Effluent](/comparisons/bre-digest-365-vs-bs-6297-drainage-field)Statutory Distinction: Part H3 vs Part H2 - [Surface Water vs Highway Drainage Rebate: B2B Tariff Comparison](/comparisons/surface-water-vs-highway-drainage-rebate)Form H/01 & CMOS Wholesale Market - [Direct Vetted Groundworkers vs Multi-Resold Lead Directories](/comparisons/vetted-groundworkers-vs-lead-directories)Engineering Dispatch vs Aggregator Directories ## 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