What Size Manhole Do I Need?

Size by Depth

• Up to 600mm deep: 450mm diameter inspection chamber (round plastic)
• 600mm–1,200mm deep: 450mm or 600×450mm rectangular chamber
• 1,200mm–3,000mm deep: 1050mm diameter or 1200×750mm manhole
• Over 3,000mm deep: 1200mm diameter minimum — person entry required

Inspection Chamber vs Manhole

An inspection chamber is a shallow access point (typically up to 1m deep) where rodding and jetting can be done from ground level. A manhole is deeper and large enough for a person to enter for maintenance. Most domestic drainage uses inspection chambers.

When You Need Access Points

• At every change of direction
• At every junction between drains
• At every change of pipe size or gradient
• At intervals not exceeding 45m on straight runs
• At the head of each drain run

Cover Types

• Class A15: Pedestrian areas only (1.5 tonne load)
• Class B125: Light vehicle traffic, driveways (12.5 tonne)
• Class D400: Public roads and heavy traffic (40 tonne)
• Recessed/block paving: For driveways and patios (infilled with matching surface)

Building Regulations

Approved Document H (drainage) requires adequate access for maintenance and clearance of blockages. The size and type of access point depends on depth, pipe size, and location. All new drainage work requires Building Control approval or must be done by an approved contractor.