What is Building Regulations Part H?

Part H of the Building Regulations covers drainage and waste disposal in England and Wales. It sets minimum standards for foul water drainage, rainwater drainage, wastewater treatment systems, and cesspools. Any new building work, extension, or drainage alteration must comply with Part H requirements.

Do I need Building Control approval for drainage work?

Yes, most drainage work requires Building Control notification or approval. This includes new drainage installations, connecting to existing drains, installing septic tanks or treatment plants, and any work that affects below-ground drainage. Minor repairs that don't change the drainage system usually don't need approval.

What are the main sections of Approved Document H?

Approved Document H has six sections: H1 (foul water drainage), H2 (wastewater treatment systems and cesspools), H3 (rainwater drainage), H4 (building over sewers), H5 (separate systems of drainage), and H6 (solid waste storage). Each section provides technical guidance for compliance.

What are the minimum drain pipe sizes under Part H?

For foul drainage, the minimum internal diameter is 75mm for waste pipes and 100mm for soil pipes and underground drains. Rainwater pipes must be at least 75mm diameter. These sizes ensure adequate flow capacity and reduce blockage risk.

Can I build over or near a public sewer?

Building over or within 3 metres of a public sewer requires written consent from your water company under Build Over Agreements. You may need a CCTV survey before and after construction. Building Control will check this as part of approval. Failure to get consent can result in enforcement action.

Building Regulations Part H: UK Drainage Compliance Guide

Approved Document H sets the standards for drainage in England and Wales. Whether you're building an extension, installing a new bathroom, or connecting to the main sewer, this guide explains what Part H requires in plain English.

Quick Answer Part H of the Building Regulations covers all aspects of drainage: foul water (toilets, sinks), rainwater (gutters, soakaways), off-mains systems (septic tanks, treatment plants), and building near sewers. Most drainage work needs Building Control approval before you start.

What Does Part H Cover?

Approved Document H is divided into six sections, each covering different drainage requirements:

H1 - Foul Water Drainage

This section covers pipes carrying waste from toilets, sinks, baths, and appliances. Key requirements include:

Minimum pipe diameter of 100mm for soil pipes and underground drains
Adequate access points (rodding eyes, inspection chambers) for maintenance
Proper gradients (falls) to ensure waste flows correctly
Ventilation to prevent trap seal loss and odours

H2 - Wastewater Treatment Systems and Cesspools

For properties not connected to mains drainage:

Septic tanks must have properly sized drainage fields
Treatment plants must meet British Standard EN 12566
Cesspools must have minimum 18,000 litre capacity
All systems must comply with General Binding Rules

H3 - Rainwater Drainage

Requirements for gutters, downpipes, and surface water disposal:

Adequate gutter and pipe sizes for roof area
Soakaways must be designed to percolation test results
Surface water must not discharge to foul sewers (in most areas)

H4 - Building Over Sewers

Special requirements when building over or near existing drains:

Public sewers require water company consent (Build Over Agreement)
CCTV survey typically required before and after construction
Foundation design must protect the sewer

H5 - Separate Systems

Requirements to keep foul and surface water drainage separate where the public sewer system requires it.

H6 - Solid Waste Storage

Requirements for bin storage and waste collection access.

When Do I Need Building Control Approval?

Work Needing Approval New drainage installations, alterations to existing drains, septic tank or treatment plant installation, connecting to public sewers, and any work affecting below-ground drainage all require Building Control notification.

Work That Usually Needs Approval

Installing new toilets, bathrooms, or kitchens with new drainage
Extending existing drainage for an extension
Installing septic tanks, treatment plants, or soakaways
Connecting new drainage to an existing system
Building over or near existing drains
Replacing defective drains if changing the route or size

Work That Usually Doesn't Need Approval

Like-for-like repairs (same size, same location)
Clearing blockages
Replacing damaged sections with identical materials
Routine maintenance and cleaning

Key Technical Requirements

Pipe Sizes (Minimum Internal Diameter)

Waste pipes (sinks, baths): 32-50mm depending on appliance
Soil pipes (toilets): 100mm minimum
Underground foul drains: 100mm minimum
Rainwater pipes: 75mm minimum

Drain Gradients (Falls)

Drains must have sufficient fall to ensure self-cleansing flow:

100mm pipes: Minimum 1:80 (1.25%), ideal 1:40 (2.5%)
150mm pipes: Minimum 1:150 (0.67%)

Access for Maintenance

Access points (inspection chambers, rodding eyes) are required at:

Changes of direction greater than 45 degrees
Changes of gradient
Junctions with other drains
Maximum 45m intervals on straight runs

Getting Approval: The Process

Option 1: Building Notice

Quick notification before starting work. Building Control will inspect as you go. Less certainty upfront but faster to start.

Option 2: Full Plans Application

Submit detailed plans for approval before starting. Takes longer but gives formal approval and certainty that your design complies.

Inspections

Building Control will want to inspect:

Before covering: Drains must be visible for inspection before backfilling
Drain testing: Air or water test to check for leaks
Connections: Inspection of junctions with existing drains
Completion: Final inspection before issuing certificate

Scotland and Northern Ireland

Part H applies to England and Wales only. Different regulations apply elsewhere:

Scotland: Building (Scotland) Regulations with separate Technical Handbooks
Northern Ireland: Building Regulations (Northern Ireland) with separate technical guidance

The principles are similar, but specific requirements may differ.