--- title: "8 Statutory Part H4 & Water Industry Act 1991 Sewer Engineering Guides (2026) | BuildOverAgreement.co.uk" source_url: "https://buildoveragreement.co.uk/guides" retrieved_by: "AnswerRail Edge Engine v1.1.0-parity-v20 (https://answerrail.com)" level_of_detail: "standard" token_payload_reduction: "93.4%" raw_html_bytes: 83846 compiled_body_bytes: 5513 entities_extracted: 4 currency_recall_static_html: "not_applicable" link_recall_static_html: "100%" monitored_content_links: 8 rfc_compliance: "RFC 9110" last_verified_at: "2026-10-17T13:30:09.832Z" cache_age_seconds: 0 origin_cache_control: "public, max-age=0, must-revalidate" --- > **Canonical Source:** [https://buildoveragreement.co.uk/guides](https://buildoveragreement.co.uk/guides) > > *Complete 2026 technical reference library covering the 3m rule, 45° zone of influence, 450mm lintel bearings, 150mm crown void formers, rocker pipes, and WRc MSCC5 CCTV surveys.* ### Organization: BuildOverAgreement.co.uk (UK Drainage & Environmental Standards Desk) | Field | Value | | :--- | :--- | | **Organization** | BuildOverAgreement.co.uk (UK Drainage & Environmental Standards Desk) | | **Official Website** | https://buildoveragreement.co.uk | | **Email** | compliance@buildoveragreement.co.uk | ### Entity: BuildOverAgreement.co.uk — UK Part H4 Sewer & Foundation Calculator | Property | Detail | | :--- | :--- | | **Type** | WebSite | | **Name** | BuildOverAgreement.co.uk — UK Part H4 Sewer & Foundation Calculator | ### Entity: BuildOverAgreement.co.uk Part H4 Compliance & Lintel CAD Calculator (2026) | Property | Detail | | :--- | :--- | | **Type** | WebApplication | | **Name** | BuildOverAgreement.co.uk Part H4 Compliance & Lintel CAD Calculator (2026) | ### Step-by-Step Procedure: How to Obtain a UK Build Over Agreement for an Extension (2026) > **Objective:** Step-by-step statutory process under Building Regulations Approved Document H4 and Section 174 Water Industry Act 1991. #### 1. Locate Public Sewer & Invert Depth Consult your CON29DW drainage search or lift the inspection chamber cover to measure sewer distance, pipe diameter (100mm–300mm), and invert depth. #### 2. Check 3.0m Trigger Zone & 45-Degree Load Cone Verify whether your new extension foundation trench falls within 3.0m horizontally of the sewer or inside the 45-degree angle of repose from the pipe invert. #### 3. Specify Foundation Depth & Bridging Lintel Excavate foundations to at least sewer invert + 150mm, and span over or near the pipe using reinforced concrete lintels with 450mm end bearings and a 150mm compressible crown void former. #### 4. Submit Free Self-Certification or Formal Dossier Lodge your 1:20 cross-section, 1:100 site plan, and WRc MSCC5 CCTV drain survey with your statutory water undertaker and Building Control before pouring concrete. Statutory Library # 8 Statutory Part H4 & Sewer Engineering Guides Comprehensive compliance reference manuals explaining Building Regulations 2010 Requirement H4 and Section 174 Water Industry Act 1991. Building Regs Part H4 6 min read ## [How Close Can I Build to a Public Sewer? (The 3-Metre Rule)](/guides/how-close-can-i-build-to-a-sewer) A definitive guide to the 3.0m statutory consultation zone, the 45-degree angle of repose, and minimum foundation clearances under UK Building Regulations Approved Document H4. Citation: Building Regs 2010 Approved Document H4 & Water Industry Act 1991 s.18 [Read Complete Guide](/guides/how-close-can-i-build-to-a-sewer) Building Regs Part H4 7 min read ## [Lateral Drain vs Public Sewer: The 2011 Transfer Act Explained](/guides/what-is-a-lateral-drain-vs-public-sewer) Understand the legal boundary between private drains you own and maintain, vs public lateral drains transferred to water companies under the landmark 2011 regulations. Citation: The Water Industry (Schemes for Adoption of Private Sewers) Regulations 2011 (SI 2011/2885) [Read Complete Guide](/guides/what-is-a-lateral-drain-vs-public-sewer) Building Regs Part H4 8 min read ## [Building Over a Manhole: Rules, Internal Covers & Chamber Relocation](/guides/building-over-manhole-rules) Why UK water companies strictly ban building over inspection chambers, and the civil engineering steps required to relocate or seal chambers. Citation: Approved Document H4 Para 1.10 & Water Industry Act 1991 s.174 [Read Complete Guide](/guides/building-over-manhole-rules) Building Regs Part H4 9 min read ## [Foundation Bridging Lintels: Structural Calculation Detail](/guides/foundation-bridging-detail-lintel) How to calculate reinforced concrete lintel spans, compressible void formers, and rocker pipe joints over public sewers. Citation: BS EN 752:2017 & Approved Document H4 Section 1 [Read Complete Guide](/guides/foundation-bridging-detail-lintel) Building Regs Part H4 6 min read ## [CCTV Drain Survey Requirements for Build Over Approval](/guides/cctv-drain-survey-requirements) Everything you need to know about pre- and post-construction CCTV camera surveys, WRc defect coding, and typical UK costs. Citation: WRc Sewerage Rehabilitation Manual & Sewer Inspection Manual (4th Edition) [Read Complete Guide](/guides/cctv-drain-survey-requirements) Building Regs Part H4 7 min read ## [Retrospective Build Over Agreements & Property Conveyancing](/guides/retrospective-build-over-agreement) What to do when selling or buying a house where an extension was built over a sewer without water company consent. Citation: Law Society Conveyancing Protocol & CML/BSA Lenders Handbook [Read Complete Guide](/guides/retrospective-build-over-agreement) Building Regs Part H4 8 min read ## [Building Regulations Approved Document H4 Explained](/guides/building-regs-part-h4-explained) A clause-by-clause walkthrough of Building Regulations 2010 Requirement H4 (Building Over Sewers). Citation: The Building Regulations 2010 Requirement H4 Schedule 1 [Read Complete Guide](/guides/building-regs-part-h4-explained) Building Regs Part H4 6 min read ## [Build Over Agreement Costs: UK Water Authority Fee Comparison](/guides/build-over-agreement-cost-uk-comparison) Direct cost comparison across Thames Water, Severn Trent, United Utilities, Anglian, Yorkshire, Southern, Wessex, and Welsh Water. 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