Building Regulations Part H Explained for Homeowners

Building Regulations Part H Explained for Homeowners

Building Regulations Part H covers drainage and waste disposal in England and Wales. For homeowners considering an extension, a basement conversion, a new bathroom or any work that touches the foul or surface water drainage system, Part H is the rulebook that decides what is legal, what is safe and what your local authority will sign off. This guide explains what Part H actually requires, when you need formal approval, what a build-over agreement is, and what happens if you skip the process. It is written for owners and small builders working on North London properties from Camden to Barnet.

What Part H covers: H1 to H6

The Building Regulations Part H is published by the Department for Levelling Up, Housing and Communities as Approved Document H. It is divided into six sections, each addressing a different element of drainage and waste management.

• H1 – Foul water drainage. Covers the design, installation and connection of pipes carrying waste from WCs, sinks, baths and appliances. Sets pipe size, gradient, ventilation and access requirements.
• H2 – Wastewater treatment systems and cesspools. Covers septic tanks, package treatment plants and cesspools. Links to the Environment Agency General Binding Rules.
• H3 – Rainwater drainage. Surface water from roofs, paved areas and yards. Covers gutters, downpipes, gullies, soakaways and connection to surface water drains.
• H4 – Building over sewers. Sets out when works built over or near a public sewer require a build-over agreement with the relevant water and sewerage undertaker, typically Thames Water in London.
• H5 – Separate systems of drainage. Requires that foul and surface water are kept separate on new developments, supporting Thames Water’s strategy of reducing combined sewer overflows.
• H6 – Solid waste storage. Bin storage capacity and access for collection.

Part H is supplemented by British Standards including BS EN 752 (drain and sewer systems outside buildings) and BS EN 12056 (gravity drainage systems inside buildings). Compliance with the British Standards is generally taken as compliance with Part H for the relevant elements.

When you need Building Regulations approval for drainage

Any new drainage installation, alteration to existing drainage, or work that affects an existing drain or sewer is notifiable under the Building Regulations. Common examples include:

• New or relocated bathrooms, WCs, kitchens or utility rooms
• Single or double-storey extensions that add fixtures or build over existing drains
• Basement conversions with new pumped foul connections
• Loft conversions with a new shower or WC
• Replacing a septic tank or installing a package sewage treatment plant
• New soakaways or surface water management systems
• Repairing or relining a drain that passes under a structure

Approval is obtained either through Local Authority Building Control (LABC) at your council, or through an Approved Inspector under the private sector route. Both routes apply the same Part H standards but differ in fees, timescales and process.

Build-over agreements (Section 106)

If you plan to build over or within three metres of a public sewer, you need a build-over agreement with the local water and sewerage undertaker. In Greater London that is Thames Water. The legal basis is Section 106 of the Water Industry Act 1991, which gives the undertaker the right to access and maintain its sewers.

The build-over process typically requires:

• A site plan showing the sewer alignment relative to the proposed structure
• A CCTV survey of the affected sewer section to grade its existing condition
• Structural calculations proving the foundations span over the sewer with adequate clearance
• Provision of access points such as new manholes outside the building footprint
• A fee, currently around £390 to £1,300 depending on complexity

Without a signed build-over agreement, your local authority may refuse to issue a completion certificate, and your conveyancing solicitor will flag the omission on any future sale. The agreement also indemnifies you against Thames Water removing the structure to access the sewer if the works obstruct its statutory duty.

Section 104 adoption agreements

A Section 104 agreement applies to new estate developments where the developer builds private drains that will subsequently become public sewers maintained by the water undertaker. The agreement sets the construction standards (typically Sewers for Adoption 7), the inspection regime and the financial bond. For individual homeowners this is rarely relevant unless you are part of a small private development.

How to ensure your works comply

For most domestic projects, compliance with Part H comes down to using a competent designer and a qualified drainage contractor.

Design checks

• Foul drain minimum gradient typically 1 in 40 for 100 mm pipe, 1 in 80 for 150 mm
• Ventilation by stack pipe extended above roof level or an approved air admittance valve
• Inspection chambers at junctions, changes of direction and at maximum spacing per BS EN 752
• Surface water disposal to soakaway in accordance with BRE Digest 365 where ground conditions permit

Installation and inspection

Pipes laid with proper bedding (typically 100 mm granular surround), correct fall and joints made strictly to manufacturer’s instruction. Building Control typically inspects at first fix (drains uncovered) and at completion with a water or air pressure test.

Materials and standards

Foul drainage materials accepted under Part H include vitrified clay to BS EN 295, PVC-U to BS EN 1401, and ductile iron to BS EN 598. Pitch fibre is no longer permitted for new work. Air admittance valves must comply with BS EN 12380. Inspection chambers and gully covers must meet the relevant load class under BS EN 124, typically B125 for residential pavements and D400 for areas trafficked by vehicles.

Documentary evidence of compliance comes through CE marking or UKCA marking on materials, plus the contractor’s installation certificate. Keep these documents with your property records as they will be requested by future buyers’ solicitors.

LABC enforcement and penalties for non-compliance

Failure to obtain Building Regulations approval is a criminal offence under the Building Act 1984. The local authority can serve an enforcement notice requiring you to alter or remove work that does not comply, and prosecute in the magistrates court. Maximum fines for individuals were unlimited following the abolition of the £5,000 cap in 2015.

In practical terms, the more common consequence is on resale. Conveyancing enquiries (CON29 and the seller’s TA6 form) ask specifically about Building Regulations approvals. A missing completion certificate triggers a retention from the sale price or, increasingly, a regularisation application that costs more than the original approval would have done.

If you discover unauthorised drainage works on a property you already own, the regularisation route under Regulation 18 of the Building Regulations 2010 allows retrospective approval. The local authority will inspect, may require opening up of completed work, and issue a regularisation certificate if satisfied. Costs are typically 1.5 to 2 times the original fee.

When to call a professional

Drainage compliance is a specialist area. Whether you need a CCTV survey for a build-over agreement, a regularisation inspection on completed works, or full design and install of a new system, a qualified drainage contractor will save time and money. Greater London Drainage handles Thames Water build-over surveys, LABC inspection support and full installation across North London. Contact our team through our drain repairs service for an initial discussion.

Final thoughts

Part H is not the most thrilling reading, but it is the legal framework that keeps drainage safe, sanitary and serviceable. The cost of doing things properly through Building Control and Thames Water’s build-over process is modest compared with the cost of getting it wrong, both in immediate enforcement and in long-term saleability. If you are planning an extension, bathroom or basement project, factor a brief consultation with a drainage specialist into your design stage. Catching a sewer alignment issue on paper is far easier than catching it once the slab is poured.