For pipes around 48 inches and larger, conventional concrete manholes or junction boxes can become very large, expensive, heavy, and slow to obtain. Prefabricated access risers attached to the pipe can reduce the need for large concrete structures, simplify installation, reduce equipment requirements, and lower material costs. They can also reduce hydraulic form losses because the flow path remains more continuous.

Inline risers should be considered when sewer pipe diameters become large enough that standard manhole structures become costly or impractical. For example, a 72-inch sewer may require a 96-inch or larger manhole structure. In the webinar case study, replacing large concrete risers with prefabricated inline risers significantly reduced material cost and allowed installation with typical excavation equipment.

Lateral connections can be prefabricated into the riser or pipe body at the required elevations and orientations. This allows the contractor to install the main pipe and riser as a manufactured component, then connect the laterals in the field. This approach avoids custom field fabrication and can simplify construction sequencing.

Prefabricated junction structures can combine multiple large incoming pipes, directional changes, and access points into a single manufactured component. This can replace a large cast-in-place junction box, reducing formwork, concrete placement, construction time, and schedule risk. One example described involved multiple 60-inch lines converging into a large prefabricated chamber with access.