Maintenance Hole Sizing
Internal dimensions driven by access, benching and pipe penetrations.
Maintenance hole size is driven by the need to work inside it: access for a person and for maintenance equipment, room for benching and channel construction, space around pipe penetrations, and clearance for any internal drop.
Minimum internal dimensions are specified by the authority and generally increase with depth or with the number and size of incoming pipes. Where a larger structure is needed for constructability, the standard minimum is a floor, not a target.
Key design considerations
- Minimum internal diameter for the depth and for the number and size of pipes.
- Working space for benching, channel shaping and jointing.
- Clearance around pipe penetrations, including for sealing systems.
- Space for steps or a ladder and for safe access past the channel.
- Additional size where an internal drop or a large number of inlets is present.
- Wall thickness and external dimensions, which also set the excavation and concrete volumes.
Design checks
- Internal diameter against the authority minimum for the depth and connections.
- Access and working space adequate for the specified maintenance method.
- Structural thickness adequate for the adopted depth and loading.
Standards and authority references
- Authority standard maintenance hole drawings
- WSA 02 (current edition)
Confirm the current edition, amendment and any local supplement before applying any of the above.
Limitations and assumptions
- Standard dimensions are not reproduced here; use the authority's current drawing set.
- Project-specific requirements may exceed the standard minimum.
Related calculators
This reference is general engineering information. Confirm requirements against WSA 02, the current Australian Standards and the local water authority's supplement before use in design, and obtain project-specific advice for the conditions at hand.